Let’s see — the Tsar Bomba nuclear weapon released the equivalent of converting about 2.3 kg of matter into energy (1).
One solar mass is about 2 x 10^30 kg, so round numbers this event released the same as 10^31 Tsar Bombas, which is … a lot of energy? That number is too big to be a good intuition pump.
Let’s try again: over the course of its entire lifetime of about 10 billion years, the sun will release about 0.034% of its mass as energy (2). So one solar mass of energy is about 3000 solar-lifetime-outputs.
So this event has released about as much energy as 45,000 suns over their entire lifetime. I’m not sure how much of the energy was released in the final few seconds of merger, but probably most of it? So… that’s a lot of energy.
> this event released the same as 10^31 Tsar Bombas, which is … a lot of energy? That number is too big to be a good intuition pump
Let me try:
To match this power with sequentially detonated bombs, one would need to set off about 10^13 Tsar Bombas (or one hydrogen bomb scaled up to 5% the mass of the Moon) every second since the Big Bang to match it. With that amount of energy, you could essentially destroy earth every second since the Big Bang.
I don't care about the anecdote and its origin (but I did read this and thank you for setting the record straight). I don't care about Bono either :) He's a singer in a band that once made great music, and got lots of money, and does some good things about it. It's the parallelism of the statements 'stop clapping' x 'stop setting off bombs' that cracked me up.
Yeah, it's alot alot :-). Over on Mastodon I asked Phil Plait (@badastro) if the "missing mass" in the universe might be a result of black holes converging[1]. He wrote up this event in his newsletter[2] and points out that when they merge, they emit more energy in that instant than every single start in the universe in the same instant. So kind of like an instant of double energy. Hard to fathom how much energy that is with my meager mammalian brain.
I can't even understand how supernovae emit like "more energy than than the sun over it's entire lifetime"
Just... how? I get what happens with fusion but the numbers are so mind boggling. And it makes what seems like a terrifying ball of fire appear as a space heater in comparison. It's nuts. The GW thing you mention is near incomprehensible to me.
One of the rather curious facts about the Sun is that its net energy emissions, on a unit-mass basis, are roughly the same as a mammalian metabolism.
That is, your body is converting mass to energy (the only way the conversion is possible) through chemical processes (ATP-mediated molecular breakdown in the Krebs cycle) at roughly the same rate that the Sun is converting mass to energy through fusion of hydrogen to helium (modulo some pathway hand-waving).
You'll need far more input chemical fuel (carbohydrates and fats, mostly) than the Sun needs of input hydrogen fuel. But the net energy release rate is roughly equivalent.
The biggest difference between you and the Sun is that it (presumably) weighs somewhat more than you do. So that per-unit-mass conversion is multiplied by a much greater mass.
At this scale it can help to think in terms of mass rather than energy. The most energy the sun could ever emit over its lifetime is if it was completely converted into energy. However, this merger emitted 15 times the mass of the sun as energy. I don't have all the numbers on tap for supernovas but given that the sun won't convert all its mass to energy, it's not hard for a supernova to convert more mass in its explosion into energy than the sun ever will.
I have read somewhere that an experiencing a supernova at sun distance would be the same as holding a hydrogen bomb to your eyeball. The energy released in these events is basically unimaginable.
It depends on the kind of supernova. Type Ia[1] is really insane. 10^44 J is a thing, that I think can blind you, even you've chosen a spot for your picnic to watch a Big Boom at distance of 1 parsec. A white dwarf made mostly of carbon burns all the carbon into oxygen in matter of seconds, and then it burns some of oxygen that was a result of burning carbon. It would like to continue brewing more and more heavy elements, but can't, because it becomes so hot, that gravity is no longer enough to keep the matter from flying away.
All the stars in the universe, burning as brightly as they are, are the tiniest fraction of additional energy compared to the 2.73°K background temperature of space. The Big Bang was very warm.
For certain values of safe. It’s close enough to strip the ozone layer, significantly increase the risk of cancer, alter the climate, and possibly cause extinctions.
At these scales, several orders of magnitude literally makes no difference.
Hydrogen bomb yields range from roughly 0.1 MT to 100 MT (the full design yield of the Tsar Bomba), or four orders of magnitude. They can be considered equivalent for the purposes of this comparison. The principle warhead of the US ICBM force, the W87 warhead, has yield of ~0.3 to 0.475 MT.
Even at a distance of several tens of metres from your eye, destructive effects would remain significant.
Assuming your 0.034% figure is correct, then one solar mass is equivalent to 2941 lifetimes of a sun's output, not 30. So 15 solar masses would be more like 44115 solar-lifetimes.
It's humbling to consider what an incredibly low-energy state we humans live in. The universe is capable of such immense energetic outputs. We're humming along at energy levels approaching zero compared to most bodies floating around in space. Crazy.
Also to put in perspective, most of the mass isn't converted to energy in either nuclear or hydrogen bombs, it's just the bond energy. Pure energy for a given quantity of matter is released only in case of annihilation-like event(merging with anti matter).
So even fusion releases max 0.7% energy of the mass
I'm not sure what happens in black hole merger.. is it an annihilation like event or is just fusion...
The black holes orbit each other, and get closer and closer. This emits gravity waves, and when they merge a large proportion of their combined mass gets emitted as gravity waves. These are what LIGO is detecting.
The bond energy is also mass . Energy is mass , If you had a nuclear reactor surrounded by gas and this setup ran a turbine which compressed a humungous spring and this whole setup was completely sealed and sits on a gigantic weighing scale. You run the nuclear reactor, the spring compresses gaining potential energy, waste heat goes into the gas molecules as kinetic energy. As the reactor progresses converting "mass to energy" does the weighing scale become lighter ?
Well, weighing scale doesn't measure mass, it measures weight. It's just scales' UI converts it to kg/lb for usability, instead of showing N it actually measures (weight is a force, and force is measured in newtons).
The energy is emitted as gravitational waves which is probably tricky to convert into usable energy and you probably can't attend more than one in your life unless you have faster-than-light travel. You're much better off visiting a supernova.
But in general it's better to have a steady and stable source of power, rather than one enormous burst of energy that you have to spend on something instantly.
Converted into energy and then escape the black hole, from which light can’t escape? That doesn’t seem to compute. And if it’s converted into gravity waves then we have an excellent obvious candidate for how most energy will escape a black hole. It won’t be waiting around for hawking radiation.
I think during the merger the event horizon must be changing rapidly, so I guess there's some(or a lot) of chance that matter can escape these merger events. The matter will already have high kinetic energy...
Need a bit of oomph to move the very fabric of this universe a bit. But energy conversation laws say its just then spread all over the place across time, just like ripples in pond, suspended into nothingness of its own little universe... or something
Tells me a bit darker thing in between the lines - the chance some advanced civilization (or us in far future if we actually survive) traveling FTL by bending space massively is next to zero, we would see (or detect soon) the evidence... unless they do it on planck-level of precision and self-contain all ripples. Nah, it really seems c is the ultimate barrier so far... depressing.
Yes! And still, gravity is so weak that that immense amount of energy translates to just a relative contraction of less than 10^-20, or about a hair's width in the distance from the Earth to the Moon.
This is because space is _stiff_. Recall Hooke’s law from high school physics. The k constant represents the stiffness of the object. A rubber band is about 50. A sky scraper, about a million. Space? About 10^46 if I recall correctly. So it takes a truly enormous amount of energy in the form of gravitational waves to be able to move space enough for it to be detectable on Earth. And the only objects that can do that are the most massive ones moving at close to the speed of light: black holes, neutron stars, supernovae (the latter would have to be very close for us to see gravitational waves from - close enough that we’d likely see it with the naked eye as well).
I was disappointed to learn that it would require billions of solar masses of energy from a black hole merger to be able to ride the gravitational wave starting at a distance of a few Schwarzschild radii. It seems like riding a plasma jet might be better.
No mass escapes. It is purely gravitational waves that are emitted. There is no sneak peek behind the event horizon curtain during a black-hole merger.
Man, that is some seriously interesting phenomena:
"The black holes appear to be spinning very rapidly—near the limit allowed by Einstein's theory of general relativity," explains Charlie Hoy of the University of Portsmouth and a member of the LVK. "That makes the signal difficult to model and interpret. It's an excellent case study for pushing forward the development of our theoretical tools."
The rotating mass drags space time around it, called frame dragging, which is different from gravitational waves. Gravitational waves consists of oscillations, which is caused by change of mass, wobbling of spinning objects, or several masses orbiting around a barycentre.
A month ago, the proposed NSF budget would shut down one of the two LIGO observatories in the US, wrecking its ability to triangulate the location of events such as this black hole merger. A shutdown would also severely damage the noise margins and detection rate. Does anyone know if the shutdown is still planned? (I couldn't find any recent info.)
I believe the proposed budget is being marked up tomorrow (July 15th, 12:00). Currently the NSF budget is set to be ~$7 billion, a 23% cut compared to FY2025. I'm not sure how this affects LIGO exactly.
I was last week at an event in Pisa at virgo ego (basically ligo's cousin). It was to celebrate the 10th anniversary of finding gravitational waves iirc. There were an actress reading from the book the director of the Italian program wrote accompanied by the sound of waves made with sax. I can't describe it with words but it was truly moving.
There were also moments dedicated to interviewing a science communicator and the director of the virgo center, and he was, let's say, quite angry at the thought of ligo losing funding. Rightfully so
the collaboration to be able to triangulate is composed of LIGO, Virgo and now KAGRA. KAGRA is not yet fully ready for longer observation runs, so for now it's basically LIGO and Virgo - and if you take offline one of three, triangulation becomes nearly useless
I think all the previous events were announced with a big delay. They have a long pipeline of checks. The signals have too much noise and it's difficult not to cheat and find fake signals in the noise. IIRC they even have a team that adds secretly fake signals to ensure the pipeline is working and after it's detected the team disclose if it's real or fake, before publication.
I'm in dire need of good news, so help me see it in an optimistic lens: can you imagine a path (even very indirect) where this kind of discovery ends up having a practical use that makes real life better here on Earth ?
(I'm not in the age-old debate about "is research useful ?" - I agree the answer is yes ; I just have a failure of imagination that prevents me from answer the question "how is this research going to be useful in the long run ?")
Just an amateur interested person here, but I think there is something very positive about these developments. There are probably more, that experts can chime in on, but one I know about is that gravitational waves can give us a signal of what happened when the universe came into existence. The cosmic microwave background radiation (CMB) is a similar thing with photons - it is a signal from the earliest photons to be emitted after the Big Bang / inflation. But the universe was opaque to photons for the first 300000 or so years. Even so cosmological theories have been confirmed and falsified based on this data. But gravitational waves are signals that originated right from the start, and are not blocked by anything unlike photons, and so likely give us much clearer information on the state of the universe when it was created. This might make new insights in fundamental physics possible (quantum mechanics, relativity).
This overlaps with the fascinating topic of multi-messenger astronomy: observing an event using photons, neutrinos, and now: gravitational waves, leading to triple-messenger astronomy, leading to (hand waves) more insights than.. otherwise.
How this might make real life better ln earth: that is a gamble, but progress in fundamental physics has frequently made life better on earth.
I wish you All the best in feeling better about the world.
> "how is this research going to be useful in the long run ?"
We don't know.
However, black holes are close to the limit of our scientific knowledge. We don't know what happens on the other side of an event horizon (and we may never know, at least not experimentally). Learning more about them means learning more about the universe, and every once in a while we make a breakthrough that leapfrogs our technology. There's nothing else that we can do with so much potential.
Most of the time though, the progress is quite 'boring', at least if you are not in a related field.
>practical< usefulness of this type of research isn't results per se - but methods of getting to them
LIGO needs extremely precise lasers, stationary platforms, extreme positioning precision, tons of supporting software - even if things "exist", the _need_ for results provide advances and improvements
astronomy itself already gave us cmos sensors (aka digital cameras) - but using your phone camera doesn't really make you think "this is caused by distance measurement to the stars"
> but using your phone camera doesn't really make you think "this is caused by distance measurement to the stars"
Maybe it should!
There's so many technologies that we use today that derive from astronomy, space exploration and similar. We don't do a good job making that point to folks.
Well, maybe it's because in the last two to three decades, for the layman, technology has been mostly delivering funny gadgets, small incremental improvements, and massive problems.
We still need fusion reactors, flying cars, telepathy and a cure for cancer yesteryear.
Instead we had 140 characters, PFAS in everything (which make the cure for cancer even more overdue) ; cars that got very much not flying but very bigger (and made the world hotter, and the fusion even more overdue) ; smartphone that makes spreading lies faster than even telepathy could ever do, etc...
But, now, sure, our flying drones are guided with "A", so the authoritarian régimes only have to point in a vague direction to get innocent people bombed.
No wonder "Yay, science" is getting a hard rep.
Thank the FSM you Americans decided to stop doing science altogether. Maybe the world needs to see that "bad research" is worse than "no research at all".
Last time we did that in Europe, it only lasted for 1000 years, and got us cool looking castles and dramatic paintings. So, art, I guess ?
Most rich civilization, to show off how great they are, have built monuments. Basically saying, look we are so rich we can redirect a big part of our society's productivity to building a magnificent piece of art. Notice, how the ancient Egyptians are remembered thousands of years later.
You should think of some research in similar ways. This is us saying, look how rich and powerful we are, we can devote a significant part of our society's productivity on discovering the very essence of this universe with no practical benefit to us. Detecting blackhole mergers is an intellectual monument.
It's only spherical in a Schwarzschild (non-rotating) black hole. A rotating black hole is called a Kerr black hole, and stuff gets weird, such as there being an oblate event horizon, a weird outer horizon called an ergosphere where spacetime gets dragged along such that it's impossible to stand still and you can accelerate objects using the black hole, a weirder inner horizon called the Cauchy horizon where time travel is possible, and a singularity in the shape of a ring. Your intuition is correct that during a merger it would be weirder still.
Edit: Updated the bit about about horizons as I research a bit more. It's complicated, and I'm still not positive I have it exactly right, but I think it's now as good as I can get it.
No matter how chaotic the merger looks, the event horizon must asymptotically become either spherical (Schwarzschild) or oblate (Kerr). The mass distribution inside doesn’t change this, general relativity doesn’t allow static “lumpy” horizons.
It’s wild how much happens in those milliseconds though. Numerical relativity papers like the one you shared from arxiv.org show the horizon “sloshing” before it stabilizes.
It cannot. The event horizon by definition prevents mass and energy from leaving (ignoring the exception of Hawking radiation here). I'm assuming your "black hole droplet" would be a tiny black hole? But if you could remove a little chunk from the black hole then you've effectively taken mass out of it, which is impossible.
It is even the case that once two black holes have overlapping event horizons (so they "touch" in a way) they can't stop touching. So two black holes can zip past one another at a small distance, but if they high-five they can't stop merging.
Sure, especially consider if singularities are not real. Then what's inside the event horizon is just some bunch of unknown material in some actual shape. Why wouldn't it be?
If singularities are real...same thing but more boring answer maybe? (the distribution just being: in the center).
There’s no reason to expect that the properties of space are different inside the event horizon than outside. Of course the direction of time turns sharply as you go inside, but otherwise space is just space.
You only get an asymmetric black hole during the milliseconds of a merger. And that asymmetry is entirely due to the mass distribution inside the black hole. The black hole only becomes spherical again once the singularities have merged. Or in the more common case of rotating black holes, they only become properly oblate again once their ringularities have merged. Either way it happens quite quickly.
I am certainly no physicist but I remember coming across academic papers in the past speculating about exactly your question. I recall one theorized about singularities being hollow with all of the mass (err was it space? spacetime?) compacted down into 2 dimensions on a shell at the surface (at least IIUC, which I probably didn't).
I think that concept might fit with the infinite time dilation preventing a merger from ever actually occurring? I'd be curious how that might differ for matter that's already inside when the critical mass is reached. (I'd also be curious to know all the creative and wacky ways in which I got the above completely wrong given that's just about inevitable.)
Mass curves space. All mass curves space all the time. You are bending the fabric of spacetime even now! Don’t try to deny it!
What does curvature mean? It means that the direction of time’s arrow is different in different places. To an observer outside of a large gravitational field, events inside the field appear to move more slowly than they would have outside of it. Black holes merely take this to an extreme. To an observer far from a black hole, a clock entering the black hole appears to slow down and finally _stop_ as it crosses the event horizon¹. But simultaneously an observer traveling with the clock observes something different. They see everything outside the black hole slow down and stop instead, while they continue to coast smoothly along. They notice nothing strange at the horizon itself; it is simply empty space with weird visuals in the distance.
This almost seems like a paradox, since the two observers each believe that the other’s clock has stopped. The reason why it’s not a paradox is that the space around the black hole is strongly curved, so strongly that the axis of time swaps place with one direction of space. At the horizon the axis of time flips over and points down into the black hole. The distant observer sees time stop because time is now edge–on, as it were. The observer falling into the black hole notices nothing weird near themselves, because both time and space still exist. Only the images of distant objects show any evidence of curvature. But the falling observer is doomed, for their own time axis now points at the singularity. Their timeline now ends abruptly, while the timeline of the distant observer extends potentially a vigintillion years.
For some edutainment on the subject, I recommend The Science Asylum. He’s done a bunch of videos on gravity and relativity, but here are two in particular:
* Explaining Gravity Using Relativistic Time Dilation <https://www.youtube.com/watch?v=F5PfjsPdBzg&list=PLOVL_fPox2K83_36YgnGisn4rxNvgq1iR&index=7>
* Why Can't You Escape a Black Hole? <https://www.youtube.com/watch?v=yPQUtuTraxs&list=PLOVL_fPox2K-zpTeryROTkmzzsMssSMWp&index=6>
¹ There are other effects too. The image of the clock _lingers_ on the horizon forever, since for it time has apparently stopped. But the redshift increases to infinity too, as the gravitational well becomes steeper, so no matter what wavelengths we observe in the image of the clock fades away beyond sight. Worse, the tidal forces caused by a real stellar–mass black hole will tear apart solid objects into a stream of plasma, even small objects. So the hypothetical black hole in our thought experiment must be very large indeed, to minimize the tidal forces enough that the clock survives the trip to the horizon intact and functional. And it can't be rotating either, since the rotation causes its own weirdness. This is the spherical cow of black holes.
Eh, space inside or outside the horizon is only different in so far as to whether it can reach our timelike infinity. Locally you cannot even tell where any horizon might be (just look at a small patch of a Penrose diagram near a horizon), they are very much something related to global properties of the spacetime. In particular it's not problematic to talk about some extended volume in spacetime occupied by mass, as long as the divergence of the stress energy tensor is 0.
The point where our notions of geometry would break down would be near the singularity, not near the horizon, and we don't even know if a volume enclosed by a horizon (i.e. anything you might call a black hole) necessarily has a singularity inside, it's just that our simple mathematical models all assume one.
The math seems to suggest R=a, or simply the spin in terms of length. It's certainly an oversimplification, as the answer will depend on the choice of metric.
Here's the best resources I've been able to find on the question. Roy Kerr himself responded to the Quora question:
> There is no Newtonian singularity at the Center of the earth and there is no singularity inside a rotating black hole. The ring singularity is imaginary. It only exists in my solution because it contains no actual matter. When a star collapses into a black hole it keeps shrinking until the centrifugal force stabilizes it. The event shell forms between the star and the outside. In 57 years no one has actually proved that a singularity forms inside, and that includes Penrose. instead, he proved that there is a light ray of finite affine length. This follows from the “hairy ball theorem”.
The stack overflow answer seems to describe the problem in terms I can better understand:
> It seems unlikely to me that you're going to be able to formulate a notion of diameter that makes sense here. Putting aside all questions of the metric's misbehavior at the ring singularity, there is the question of what spacelike path you want to integrate along. For the notion of a diameter to make sense, there would have to be some preferred path. Outside the horizon of a Schwarzschild black hole, we have a preferred stationary observer at any given point, and therefore there is a preferred radial direction that is orthogonal to that observer's world-line. But this doesn't work here.
It is difficult to talk about the shape of the event horizon because the ordinary definition of a sphere is "surface where all points are equidistant from a given point" is already complex in a differentiable manifold, but even more so when the distance is infinite because of a singularity (or the point doesn't exist/isn't unique because of geodesic structure). So you switch to a definition of "surface of constant scalar curvature with the topology of a sphere", the topology being important to distinguish it from a plane and a hyperboloid.
From there, I haven't personally done or seen the calculations of the shape of the horizon for Kerr or merging black holes, but my intuition is that it would be indeed peanut shaped for a merger (there are likely some saddle points). The coordinate shape certainly is but you can choose coordinates so that a Schwarzschild black hole is a coordinate peanut so coordinates aren't very meaningful.
From our perspective there is no event horizon since the collapsing star has not reached the black hole state. In fact it takes infinite amount of time from the point of view of an external observer for the event horizon to form.
In almost all situations it does matter as the collapsing star will behave as it is a black hole. But for the merge of black holes it is significant as it allows to release energy as there is no event horizon.
Edit: "The Kerr metric also predicts the existence of an inner and outer event horizon, with the shape of these horizons being oblate rather than perfectly spherical due to the rotation."
Kind of. Because the black hole drags space around with it you need to go faster near the ‘equator’ than the poles just to stand still. So the event horizon is fatter at the equator.
I'm no physicist but what I've learned on the internet through osmosis, I'd wager that black holes aren't spherical per-se, but they appear sphere-like to us dimensionally challenged beings. It's more like a manifold (mobius-gate? not a mobius surface), that changes your spatial directions to parallel temporal directions to spatial ones all leading to the singularity.
The thing is that the spacetime around blackholes get curved to the actual extremes.
When we imagine flying "at nearly the speed of light" towards something thats traveling the same speed towards you, we tend to imagine a collision at high speeds.
But for blackholes that turn space into time and time into space, they can see the other blackhole slowing to a complete stop as its about to touch. Or it can look differently, it all depends on the position and speed of an observer.
We cant even agree on the basics like: "It doesnt matter how it looks, but they must collide", since if we look at something falling into a blackhole (which I pressume could be another blackhole just as well), we see it slow towards 0 at the edge and fade away in redshift instead of seeing it actually fall trough.
To answer my own question, some lay research shows it seems it is technically possible for them not to merge if only a tiny portion of their apparent event horizons merge and for only very briefly.
But this is because of a distinction between the Apparent Horizon [1] (which is coordinate-dependent) and the true global event horizon. So they appear to briefly merge but no true global event horizon forms to encompass both. I think!
So, if two black holes, each with mass M, were moving at nearly the speed of light and collided head-on (resulting in a final velocity of zero), what would happen to all that momentum? Would the resulting black hole have a mass greater than 2M? If so, how and why would this occur?
I think I'm going to answer my own question by saying both momentum and energy are conserved. The momentum of the entire system was zero before and after the collision. Energy must also be conserved, and since the final object is at rest, all the kinetic energy gets converted into rest mass energy, minus what is radiated away as gravitational waves.
I'm not a physicist, but I took a class on special relativity in college, and I still remember some of it ... If I'm remembering it right, we still have conservation of momentum and energy in special relativity, with the caveat that these are defined differently than in classical mechanics. Specifically, E = γmc^2 and p = mvγ, where γ = 1 / sqrt(1 - v^2/c^2) and m is the invariant mass (aka the "rest mass"). [1] Note that when v=0 (so γ=1), this equation for momentum is the same as the classical p=mv, which is generally a good approximation when v << c.
So, using those relativistic definitions for energy and momentum, I think you're exactly right, at least up to the part about "since the final object is at rest". However:
- As I understand it, invariant mass, aka "rest mass" (which is equivalent to "rest energy", aka "rest mass energy"), is invariant, and it's the same before and after the collision, so the kinetic energy doesn't get "converted into rest mass energy". Rather, if the final object is at rest, then all of its kinetic energy has been radiated away; kinetic energy (E_K) is is total energy (E) minus rest energy (E_0 = mc^2, where m is invariant mass)
- I have no idea whether gravitational waves are the only way for the kinetic energy to be radiated away. I imagine other forms of energy could also be emitted.
- In order to know that the final object is at rest/has no kinetic energy (in an inertial frame), I worry that we might need to have specified more in the original question. In particular, I don't know how to handle spin. (I know that black holes have some concept of "spin", but I don't know if this is like rotational spin, or more like quantum mechanical spin, or something else, and I don't know how it figures into the black holes' total energy.) If we change the original question to say that the black holes are not spinning, then I think we can ignore this (since the collision is head-on).
Energy and momentum are always conserved in EVERY physical process. We can distinguish three types of collisions: “sticky” ones, in which the kinetic energy decreases (typically, it is converted into heat); “explosive” ones,
where the kinetic energy increases; and elastic ones, in which the kinetic energy is conserved. Since the total energy (rest plus kinetic) is always conserved, it follows that rest energy (and hence also mass) increases in a sticky collision, decreases in an explosive collision, and is unchanged in an elastic collision. The resulting black hole in other words would have way more of a mass than 2M since you're talking about a 'sticky' collision in the above instance. You can see an example of why this is in Griffiths' text (Introduction to Elementary Particles (which I highly recommend)) -- page 101 contains a great example of what happens to the mass of particles in 'sticky' collisions: https://www.hlevkin.com/hlevkin/90MathPhysBioBooks/Physics/Q...
That is about something entirely different. It more or less just says that energy might be lost if you have a flux towards infinity. It does not in any way claim e.g. that the divergence of the stress energy tensor is non-zero (which would be how I think most people would interpret energy/momentum conservation).
My hunch is they would briefly pancake and much of the mass/energy contribution from their initial velocities would dissipate as incredibly high amplitude gravitational waves from the ring-down.
It would create a universe, obviously. First all the mass would attempt being squished at a singularity. WHILE the squishing continues, the first-in-line stuff would've already started to explode back-out inside the event horizon. From the inside viewpoint, this looks like the big bang. Once all the mass from the two black holes collide and loose momentum, the inside-universe no longer expands as fast. Things wobble a bit as all this happens, creating tangles and non-homogeneity. Could be caused by initial Planck-scale uncertainties even when having a perfect head-on collision.
The escape velocity from inside the event horizon is faster than the speed of light, which is the highest possible speed in the universe.
So black holes cannot approach each other faster than the speed of light. And if their trajectories intersect perfectly, they won’t be able to escape each other’s gravity.
A black hole can’t pass “through” another black hole like two bullets hitting each other. More like two incredibly strong magnets hitting each other in midair.
What happens when black holes collide? Does one black hole “consume” the other? Do they become a larger black hole? Does it get more dense or just larger?
They become a larger black hole, mostly conserving mass, minus a few percent to gravitational waves. However, their mass is proportional to their radius, not volume, so it gets LESS dense. If you laid out a bunch of black holes in a line, just barely not touching, and let them merge, suddenly, the whole sphere of space enclosing the line becomes black hole. It also turns out that a black hole with the mass of the universe would have a volume about the size of the universe.
Is that intended to be a correction? (I don't think the original statement needs correcting, other than by replacing "universe" with "observable universe" in both places.)
Up until the universe was around a few billion years old, its Schwarzchild radius would have been larger than even the co-moving (not just observable) universe's radius, but the initial momentum from the big bang was high enough to prevent collapse.
That sounds suspiciously like "they were inside a region with enough mass to form an event horizon, but they escaped because they had enough momentum", which in turn sounds like "we can escape from inside an event horizon if we just move fast enough". Can you explain how that's not what you're saying?
I wish I had a straightforward answer to that. I'm sure the answer is some combination of cosmic inflation and dark energy, but by all means it appears the early universe either narrowly escaped, or simply is a black hole, that singularities are a flawed concept, that nothing is escaping the universe, and we are all stuck moving forward in time, and that the infinite future is the singularity.
I don't have an answer either. But in my amateur opinion, of the available options, I lean toward "is a black hole". If all the mass we can see adds up to a black hole the size of what we can seen, then if you add all the stuff outside the light cone, it should add up to enough mass to make a black hole radius that includes the distance out to there.
But that leaves us with black holes forming inside a black hole, which I have absolutely no idea what to do with.
Ohh, I see, you mean "mass" should have been "mass and energy" rather than e.g. that (mass,volume) should have been replaced by (mass,energy) or something.
I confess I just ... take it for granted in this kind of context that "mass" or "energy" or "mass+energy" all mean the same thing. Someone who wants to refer just to the total amount of matter will say something like "the total mass of the matter in the universe".
It's commonplace for physicists to write just "mass" when talking about this sort of thing. E.g.,
"Theories involving the parameters h, c, G, H (in a usual notation) are considered. A huge ratio of 10^120 of the mass of the universe (m_u) to the smallest determinable mass m_0 in the period since the big bang occurs in such theories."
(Not cherry-picked; I went to the Wikipedia article on "Black hole cosmology", noted that it just says "mass" rather than "mass-energy" or whatever, and followed the link in the attached footnote. Also, so far as I know, not crankery; Landsberg was an eminent physicist.)
Can't we generalize to say that we observe that black holes have a similar density (which is to say, proportion of mass to volume) any sample of the observable universe sufficiently large as to be roughly uniform?
In other words, doesn't this observation scale both down (to parts of the universe) and up (beyond the cosmological horizon, presuming that the rough uniformity in density persists), at least for any universe measured in euclidian terms?
It's very possible that I'm wrong here, and I'd love to be corrected.
...I also think we have to acknowledge that "similarly" is doing a fair bit of work here, as we're not accounting for rate of expansion - is that correct?
Thanks, I was kinda curious why it wasn't full of spam. it's running on a super neglected rpi, really need to wipe it and spend a month refreshing myself on basic webhosting stuff
For normal matter inspiraling, yes, but a black hole which is falling into a black hole doesn't get to glow in gamma rays to try to escape :) they can only lose mass/energy by making splashes in spacetime itself (or hawking radiation)
They become a more massive one. The volume of a black hole (assuming you're measuring at the event horizon) is determined only by its mass, so the final density is the same as you'd get for any other black hole of that mass regardless of how it came to be.
I don't know how to address the "consume" question. If you were pulling on a piece of fabric and two tears in it grew until they met each other to become one tear... would you say that the larger one consumed the smaller?
My guess is that in some popular depictions black holes are like holes, and things fall in the holes, and even a small black hole can possible fall inside a bigger hole.
A better image is too drops of water on a glass, add some black ink for bonus realism. They merge into a bigger drop. Except, obviously black holes are not filled with water. And the "average density" of the new black hole is smaller then the "average density" of both original black holes, unlike the density of water drops on a glass. So don't take this image too literaly.
(There are some problems to define the "density" of a black hole, but let's ignore all of them.)
> The volume of a black hole (assuming you're measuring at the event horizon) is determined only by its mass, so the final density is the same as you'd get for any other black hole of that mass regardless of how it came to be.
Wait, really? So if you had a super massive disk that was just 1 electron away from having enough mass to become a black hole... and then an electron popped into existence due to quantum randomness... then it would become a sphere instantly? Wouldn't that violate the speed of light or something?
Event horizons are non-physical. Better to think of it as "then a spherical event horizon would become apparent." When the mass within a given black-hole-shaped volume (spherical for non-rotating mass) is "one electron short" of being a black hole, then one can define a surface in the shape of the (future) black hole where the escape velocity is /just/ below the speed of light. In practice, all light emitted within that volume will already be captured by the mass, unless it's perfectly perpendicular to the (future) event horizon. When that extra electron is added, it becomes true that the escape velocity at that same surface is now the speed of light -- the definition of event horizon. But nothing needs to "form" to make this true.
Your disk will emit a lot of gravitational on electromagnetic radiation, and after a while it will be a nice sphere. (Unless it's rotating and it will be a nice somewhat-elipsoidal ball.)
---
> and then an electron popped into existence due to quantum randomness
I feel there is a huge can of worms of technical problems in this sentence that nobody know how to solve for now. Just in case replace the quantum randomness with a moron with a broken CRT used as an electron cannon.
The analogy I like goes something like this. Imagine you're paddling in a canoe on the river. You approach a waterfall. If you do nothing you'll get consumed by the waterfall. So you try to paddle away from the waterfall, but as you get closer to the edge of the waterfall, the current gets stronger.
The event horizon is the imaginary line across the river which once passed, even if you paddle as quickly as you can, you won't be able to get away from the waterfall. Once you pass that line, you're bound to reach the waterfall eventually.
Now, thanks to Maxwell and Einstein, we know there's a maximum speed that anyone can paddle, the speed of light, and so we define the event horizon to be relative to this speed.
You can calculate the event horizon for just about anything. The main difference between a black hole and everything else, is that for a black hole the event horizon is larger than the object itself.
For example, the event horizon of a neutron star with a mass of 1.4 solar masses and a radius of 10km is about 4.1 km, well inside the neutron star. Thus you don't get the "black hole effect", since once you pass the surface of the neutron star the matter above you pulls you away from the center.
The river analogy is actually not far off what they try to use as an analog for testing black hole predictions, effectively a large water tank with a drain hole. Sixty Symbols did a video on this way back[1], and this thesis[2] goes into the details. Some are going beyond water using liquid helium to simulate quantum black holes this way[3].
Long before your disc neared the mass where it would form an event horizon, the matter it's made of would collapse into neutron star material, which would form a sphere.
Perhaps if it were exceptionally wide the whole disc wouldn't collapse. Maybe only the parts near it's center. In that case you'd end up with a large ring around a neutron star. Add a bit more mass and maybe it's now a ring around a black hole. The gravity of the ring might distort the event horizon in some way, I'm not sure quite how, but probably its possible to get a non-spherical hole in situations where the objects distorting the shape are still in the universe.
But as for the matter lost into the hole, it's gone. If the hole were to retain some shape based on what's "inside" of it, that would be the kind of information leak that the laws of physics do not permit.
That electron would take an infinite amount of time to reach the edge, since time dilates to infinity with gravity that strong.
> a sphere instantly
The concept of instantly doesn't work with time dilation like this. What you see will be different depending on if you are also falling in, or if you are far away.
My understanding is they just spiral into each other forever.
From our point of view nothing can actually fall into a black hole, instead it time dilates into nothing. "It is true that objects that encounter the event horizon of a black hole would appear “frozen” in time"[1]
So we would never actually see the black holes merge. In fact I'm not clear how a black hole can even form in the first place, since it would take an infinite amount of time to do so (again, from our POV).
(And yes, I know that from the POV of the falling object, they just fall in like normal. But that doesn't help us, because we'll never see it.)
This is true, but it's not an observable distinction. It's true that in some sense those two black holes "haven't yet collided", but at this point they're well past the point of last observability and have now red shifted and time dilated into the invisible background. All the interesting stuff happens before that.
My basic understanding is that they combine, basically you just add the masses together. That increased mass then means more gravity, so the event horizon is pushed further out.
We can't REALLY answer questions about what's inside the event horizon, but some real work has been done on what BH mergers look like, though even that as I understand, is extremely difficult model.
These kinds of simulations inherently cannot model the singularity accurately whatsoever. At the singularity, the numerical technique used becomes knowingly invalid
In fact, the entire interior of the event horizon is actually physically invalid in these simulations. The formalisms used trap the errors inside the event horizon, as the errors turn out to be strictly causal. And because of that, theoretically they can't escape
Of course that analysis breaks down in the face of discretisation, so errors tend to leak out a bit under low resolutions, so you have to handle things pretty careful. Either way, you shouldn't draw any conclusions about the interior
Everything in the universe is massive because we are just so small. Everywhere but within the confines of our solar system, calling something massive is a meaningless endeavour, it’s so big nobody has any idea how to appreciate it, and then there is always going to be something bigger which makes that black hole look tiny
In case it's not clear, that 'chirp' is exactly what we would hear if the merger was powerful enough to actually be detectable by our ears. It's the vibration induced in the final moments and the frequency is the speed at which the blackholes are orbiting each other before they merge. Things the size of multiples of our Sun dancing around each other a thousand times per second. It's insane to me.
When I read 'news' like that, I 'compare' myself to the thing. And then I think how this 'thing' can swallow me, everyone around me, everything as far as the eye can see (thank you light pollution, we can only see the moon and perhaps 5-6 more 'things' out there (ffs!)) and then we will be 'no more'.
But then I use the voice of Djimon Hounsou and the quote from the Gladiator "but not just yet".
> the 225-solar-mass black hole was created by the coalescence of black holes each approximately 100 and 140 times the mass of the Sun.
Does this mean that 15 solar masses were converted into energy? Because that's a LOT of energy.
Let’s see — the Tsar Bomba nuclear weapon released the equivalent of converting about 2.3 kg of matter into energy (1).
One solar mass is about 2 x 10^30 kg, so round numbers this event released the same as 10^31 Tsar Bombas, which is … a lot of energy? That number is too big to be a good intuition pump.
Let’s try again: over the course of its entire lifetime of about 10 billion years, the sun will release about 0.034% of its mass as energy (2). So one solar mass of energy is about 3000 solar-lifetime-outputs.
So this event has released about as much energy as 45,000 suns over their entire lifetime. I’m not sure how much of the energy was released in the final few seconds of merger, but probably most of it? So… that’s a lot of energy.
(1) https://faculty.etsu.edu/gardnerr/einstein/e_mc2.htm
(2) https://solar-center.stanford.edu/FAQ/Qshrink.html
> this event released the same as 10^31 Tsar Bombas, which is … a lot of energy? That number is too big to be a good intuition pump
Let me try:
To match this power with sequentially detonated bombs, one would need to set off about 10^13 Tsar Bombas (or one hydrogen bomb scaled up to 5% the mass of the Moon) every second since the Big Bang to match it. With that amount of energy, you could essentially destroy earth every second since the Big Bang.
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I don’t want to dismiss your memory of the anecdote, but it doesn’t hold up under fact-checking. https://www.snopes.com/fact-check/bono-of-contention/
I don't care about the anecdote and its origin (but I did read this and thank you for setting the record straight). I don't care about Bono either :) He's a singer in a band that once made great music, and got lots of money, and does some good things about it. It's the parallelism of the statements 'stop clapping' x 'stop setting off bombs' that cracked me up.
Yeah, it's alot alot :-). Over on Mastodon I asked Phil Plait (@badastro) if the "missing mass" in the universe might be a result of black holes converging[1]. He wrote up this event in his newsletter[2] and points out that when they merge, they emit more energy in that instant than every single start in the universe in the same instant. So kind of like an instant of double energy. Hard to fathom how much energy that is with my meager mammalian brain.
[1] https://mastodon.social/@badastro/114852139083587160
[2] https://badastronomy.beehiiv.com/p/the-biggest-black-hole-me...
I can't even understand how supernovae emit like "more energy than than the sun over it's entire lifetime"
Just... how? I get what happens with fusion but the numbers are so mind boggling. And it makes what seems like a terrifying ball of fire appear as a space heater in comparison. It's nuts. The GW thing you mention is near incomprehensible to me.
One of the rather curious facts about the Sun is that its net energy emissions, on a unit-mass basis, are roughly the same as a mammalian metabolism.
That is, your body is converting mass to energy (the only way the conversion is possible) through chemical processes (ATP-mediated molecular breakdown in the Krebs cycle) at roughly the same rate that the Sun is converting mass to energy through fusion of hydrogen to helium (modulo some pathway hand-waving).
You'll need far more input chemical fuel (carbohydrates and fats, mostly) than the Sun needs of input hydrogen fuel. But the net energy release rate is roughly equivalent.
The biggest difference between you and the Sun is that it (presumably) weighs somewhat more than you do. So that per-unit-mass conversion is multiplied by a much greater mass.
At this scale it can help to think in terms of mass rather than energy. The most energy the sun could ever emit over its lifetime is if it was completely converted into energy. However, this merger emitted 15 times the mass of the sun as energy. I don't have all the numbers on tap for supernovas but given that the sun won't convert all its mass to energy, it's not hard for a supernova to convert more mass in its explosion into energy than the sun ever will.
You mean "every single star in the universe", right?
In the visible universe. The universe may well be infinite.
Observable universe. Dark matter does not emit light.
I have read somewhere that an experiencing a supernova at sun distance would be the same as holding a hydrogen bomb to your eyeball. The energy released in these events is basically unimaginable.
Probably here:
https://what-if.xkcd.com/73/
And it’s even more astonishing — the supernova at 1 AU would be the same as a billion hydrogen bombs at your eyeball.
But you are safe at a parsec. Showing how also incredibly big space is. Space's bigness makes it hard to blow up a galaxy. Big bang excepted.
It depends on the kind of supernova. Type Ia[1] is really insane. 10^44 J is a thing, that I think can blind you, even you've chosen a spot for your picnic to watch a Big Boom at distance of 1 parsec. A white dwarf made mostly of carbon burns all the carbon into oxygen in matter of seconds, and then it burns some of oxygen that was a result of burning carbon. It would like to continue brewing more and more heavy elements, but can't, because it becomes so hot, that gravity is no longer enough to keep the matter from flying away.
[1] https://en.wikipedia.org/wiki/Type_Ia_supernova
All the stars in the universe, burning as brightly as they are, are the tiniest fraction of additional energy compared to the 2.73°K background temperature of space. The Big Bang was very warm.
For certain values of safe. It’s close enough to strip the ozone layer, significantly increase the risk of cancer, alter the climate, and possibly cause extinctions.
Space is big and quadratic function grows fast
Another way to look at it is that a hydrogen bomb is very small at planetary scale and so microscopically small at any astronomical scale.
I appreciate this point – it would take quite a few Tsar Bombas to approach the binding energy of a planet.
But, is it a small or large hydrogen bomb? And, what distance from your eyeball?
At these scales, several orders of magnitude literally makes no difference.
Hydrogen bomb yields range from roughly 0.1 MT to 100 MT (the full design yield of the Tsar Bomba), or four orders of magnitude. They can be considered equivalent for the purposes of this comparison. The principle warhead of the US ICBM force, the W87 warhead, has yield of ~0.3 to 0.475 MT.
Even at a distance of several tens of metres from your eye, destructive effects would remain significant.
I’ll run some tests and let you know
Assuming your 0.034% figure is correct, then one solar mass is equivalent to 2941 lifetimes of a sun's output, not 30. So 15 solar masses would be more like 44115 solar-lifetimes.
Derp yes, pesky off-by-100 errors :) Fixed, thanks.
It's humbling to consider what an incredibly low-energy state we humans live in. The universe is capable of such immense energetic outputs. We're humming along at energy levels approaching zero compared to most bodies floating around in space. Crazy.
If you consider orders of magnitude from the Planck scale all the way up to the observable universe, we are actually somewhere in the middle
Also to put in perspective, most of the mass isn't converted to energy in either nuclear or hydrogen bombs, it's just the bond energy. Pure energy for a given quantity of matter is released only in case of annihilation-like event(merging with anti matter). So even fusion releases max 0.7% energy of the mass
I'm not sure what happens in black hole merger.. is it an annihilation like event or is just fusion...
The black holes orbit each other, and get closer and closer. This emits gravity waves, and when they merge a large proportion of their combined mass gets emitted as gravity waves. These are what LIGO is detecting.
The bond energy is also mass . Energy is mass , If you had a nuclear reactor surrounded by gas and this setup ran a turbine which compressed a humungous spring and this whole setup was completely sealed and sits on a gigantic weighing scale. You run the nuclear reactor, the spring compresses gaining potential energy, waste heat goes into the gas molecules as kinetic energy. As the reactor progresses converting "mass to energy" does the weighing scale become lighter ?
Well, weighing scale doesn't measure mass, it measures weight. It's just scales' UI converts it to kg/lb for usability, instead of showing N it actually measures (weight is a force, and force is measured in newtons).
Is it physically limiting for a theoretical civilization to harness and use such energy?
The energy is emitted as gravitational waves which is probably tricky to convert into usable energy and you probably can't attend more than one in your life unless you have faster-than-light travel. You're much better off visiting a supernova.
But in general it's better to have a steady and stable source of power, rather than one enormous burst of energy that you have to spend on something instantly.
Converted into energy and then escape the black hole, from which light can’t escape? That doesn’t seem to compute. And if it’s converted into gravity waves then we have an excellent obvious candidate for how most energy will escape a black hole. It won’t be waiting around for hawking radiation.
I think during the merger the event horizon must be changing rapidly, so I guess there's some(or a lot) of chance that matter can escape these merger events. The matter will already have high kinetic energy...
Into what form of energy is that mass converted?
Maybe all of it is gravitational waves?
I don't think much else would escape the black hole environment.
Need a bit of oomph to move the very fabric of this universe a bit. But energy conversation laws say its just then spread all over the place across time, just like ripples in pond, suspended into nothingness of its own little universe... or something
Tells me a bit darker thing in between the lines - the chance some advanced civilization (or us in far future if we actually survive) traveling FTL by bending space massively is next to zero, we would see (or detect soon) the evidence... unless they do it on planck-level of precision and self-contain all ripples. Nah, it really seems c is the ultimate barrier so far... depressing.
> Need a bit of oomph to move the very fabric of this universe a bit.
It’s enough “oomph” that we can detect it more than half way across the universe.
Kinetic energy is another option
Pure energy.
It's hard to wrap your head around, but that's more energy than all the stars in the observable universe combined put out during that instant
Yes! And still, gravity is so weak that that immense amount of energy translates to just a relative contraction of less than 10^-20, or about a hair's width in the distance from the Earth to the Moon.
This is because space is _stiff_. Recall Hooke’s law from high school physics. The k constant represents the stiffness of the object. A rubber band is about 50. A sky scraper, about a million. Space? About 10^46 if I recall correctly. So it takes a truly enormous amount of energy in the form of gravitational waves to be able to move space enough for it to be detectable on Earth. And the only objects that can do that are the most massive ones moving at close to the speed of light: black holes, neutron stars, supernovae (the latter would have to be very close for us to see gravitational waves from - close enough that we’d likely see it with the naked eye as well).
Do we know how far this event was from earth? Wouldn't that distance be the determiner of what the relative contraction observed on earth would be?
estimated distance of 2.2 Gpc per https://en.wikipedia.org/wiki/GW231123
That's 7.2 billion light years. More than halfway to the most distant galaxy the Webb telescope has found.
So this event happened 7.2 billion years ago.
There is no mention of in which direction. Maybe the triangulation wasn't working at the time. You need three LIGOs for that.
That's how fast the millennium falcon goes
At 10 times the Schwarzschild radius Space literally stretches and contracts by 10-100%
Sure but we are 7 billion lightyears away from the source of the waves. Imagine if we'd be a bit closer ..
I was disappointed to learn that it would require billions of solar masses of energy from a black hole merger to be able to ride the gravitational wave starting at a distance of a few Schwarzschild radii. It seems like riding a plasma jet might be better.
(Just planning my next trip.)
Much better off just chucking 90% of your mass into the blackhole to get a hella kick.
Can some of the mass escape as gas/mass flying out into space? Basically is energy the only way for mass to exit such an event?
No mass escapes. It is purely gravitational waves that are emitted. There is no sneak peek behind the event horizon curtain during a black-hole merger.
Yes. Black hole mergers are the highest energy events in the universe in terms of watts.
Man, that is some seriously interesting phenomena:
"The black holes appear to be spinning very rapidly—near the limit allowed by Einstein's theory of general relativity," explains Charlie Hoy of the University of Portsmouth and a member of the LVK. "That makes the signal difficult to model and interpret. It's an excellent case study for pushing forward the development of our theoretical tools."
It's like nature handed us a stress test for general relativity
Does the spinning of a spherical object cause any gravitational waves?
The rotating mass drags space time around it, called frame dragging, which is different from gravitational waves. Gravitational waves consists of oscillations, which is caused by change of mass, wobbling of spinning objects, or several masses orbiting around a barycentre.
A month ago, the proposed NSF budget would shut down one of the two LIGO observatories in the US, wrecking its ability to triangulate the location of events such as this black hole merger. A shutdown would also severely damage the noise margins and detection rate. Does anyone know if the shutdown is still planned? (I couldn't find any recent info.)
https://www.science.org/content/article/trump-s-proposed-cut...
I believe the proposed budget is being marked up tomorrow (July 15th, 12:00). Currently the NSF budget is set to be ~$7 billion, a 23% cut compared to FY2025. I'm not sure how this affects LIGO exactly.
https://appropriations.house.gov/sites/evo-subsites/republic...
I had read something less recent than what you posted, but in that is said about 40% of ligo funding would be cut https://www.science.org/content/article/trump-s-proposed-cut...
Then again, your file has less drastic reductions on nsf budget so who knows what would be the impact on ligo
I wonder why Bezos doesn’t just pick up the tab, he likes space, right?
> I believe the proposed budget is being marked up tomorrow (July 15th, 12:00)
Interesting that they break this news today. Props to them for playing the game.
I was last week at an event in Pisa at virgo ego (basically ligo's cousin). It was to celebrate the 10th anniversary of finding gravitational waves iirc. There were an actress reading from the book the director of the Italian program wrote accompanied by the sound of waves made with sax. I can't describe it with words but it was truly moving.
There were also moments dedicated to interviewing a science communicator and the director of the virgo center, and he was, let's say, quite angry at the thought of ligo losing funding. Rightfully so
Keep an eye on whether the final FY 2026 appropriations bill keeps LIGO at two sites. Until then, it’s a real risk, but salvageable.
Given that there’s a handful of gravitational-wave observatories running globally at this point, why does the closure of one LIGO wreck triangulation?
the collaboration to be able to triangulate is composed of LIGO, Virgo and now KAGRA. KAGRA is not yet fully ready for longer observation runs, so for now it's basically LIGO and Virgo - and if you take offline one of three, triangulation becomes nearly useless
Looking at their Grafana dashboard, it looks like GEO600 and KAGRA are both observing? https://online.ligo.org/grafana/public-dashboards/1a0efabe65...
So maybe that is why this discovery from 2023 gets published right now.
I think all the previous events were announced with a big delay. They have a long pipeline of checks. The signals have too much noise and it's difficult not to cheat and find fake signals in the noise. IIRC they even have a team that adds secretly fake signals to ensure the pipeline is working and after it's detected the team disclose if it's real or fake, before publication.
I'm in dire need of good news, so help me see it in an optimistic lens: can you imagine a path (even very indirect) where this kind of discovery ends up having a practical use that makes real life better here on Earth ?
(I'm not in the age-old debate about "is research useful ?" - I agree the answer is yes ; I just have a failure of imagination that prevents me from answer the question "how is this research going to be useful in the long run ?")
Just an amateur interested person here, but I think there is something very positive about these developments. There are probably more, that experts can chime in on, but one I know about is that gravitational waves can give us a signal of what happened when the universe came into existence. The cosmic microwave background radiation (CMB) is a similar thing with photons - it is a signal from the earliest photons to be emitted after the Big Bang / inflation. But the universe was opaque to photons for the first 300000 or so years. Even so cosmological theories have been confirmed and falsified based on this data. But gravitational waves are signals that originated right from the start, and are not blocked by anything unlike photons, and so likely give us much clearer information on the state of the universe when it was created. This might make new insights in fundamental physics possible (quantum mechanics, relativity).
This overlaps with the fascinating topic of multi-messenger astronomy: observing an event using photons, neutrinos, and now: gravitational waves, leading to triple-messenger astronomy, leading to (hand waves) more insights than.. otherwise.
How this might make real life better ln earth: that is a gamble, but progress in fundamental physics has frequently made life better on earth.
I wish you All the best in feeling better about the world.
> "how is this research going to be useful in the long run ?"
We don't know.
However, black holes are close to the limit of our scientific knowledge. We don't know what happens on the other side of an event horizon (and we may never know, at least not experimentally). Learning more about them means learning more about the universe, and every once in a while we make a breakthrough that leapfrogs our technology. There's nothing else that we can do with so much potential.
Most of the time though, the progress is quite 'boring', at least if you are not in a related field.
>practical< usefulness of this type of research isn't results per se - but methods of getting to them
LIGO needs extremely precise lasers, stationary platforms, extreme positioning precision, tons of supporting software - even if things "exist", the _need_ for results provide advances and improvements
astronomy itself already gave us cmos sensors (aka digital cameras) - but using your phone camera doesn't really make you think "this is caused by distance measurement to the stars"
> but using your phone camera doesn't really make you think "this is caused by distance measurement to the stars"
Maybe it should!
There's so many technologies that we use today that derive from astronomy, space exploration and similar. We don't do a good job making that point to folks.
Well, maybe it's because in the last two to three decades, for the layman, technology has been mostly delivering funny gadgets, small incremental improvements, and massive problems.
We still need fusion reactors, flying cars, telepathy and a cure for cancer yesteryear.
Instead we had 140 characters, PFAS in everything (which make the cure for cancer even more overdue) ; cars that got very much not flying but very bigger (and made the world hotter, and the fusion even more overdue) ; smartphone that makes spreading lies faster than even telepathy could ever do, etc...
But, now, sure, our flying drones are guided with "A", so the authoritarian régimes only have to point in a vague direction to get innocent people bombed.
No wonder "Yay, science" is getting a hard rep.
Thank the FSM you Americans decided to stop doing science altogether. Maybe the world needs to see that "bad research" is worse than "no research at all".
Last time we did that in Europe, it only lasted for 1000 years, and got us cool looking castles and dramatic paintings. So, art, I guess ?
Most rich civilization, to show off how great they are, have built monuments. Basically saying, look we are so rich we can redirect a big part of our society's productivity to building a magnificent piece of art. Notice, how the ancient Egyptians are remembered thousands of years later.
You should think of some research in similar ways. This is us saying, look how rich and powerful we are, we can devote a significant part of our society's productivity on discovering the very essence of this universe with no practical benefit to us. Detecting blackhole mergers is an intellectual monument.
I've always thought the event horizon for a black hole has to be spherical.
But my physics intuition tells me that as two of them merge, the resulting BH should have a "peanut" shape, at least initially.
And maybe it can keep having an irregular shape, depending on the mass distribution inside it?
It's only spherical in a Schwarzschild (non-rotating) black hole. A rotating black hole is called a Kerr black hole, and stuff gets weird, such as there being an oblate event horizon, a weird outer horizon called an ergosphere where spacetime gets dragged along such that it's impossible to stand still and you can accelerate objects using the black hole, a weirder inner horizon called the Cauchy horizon where time travel is possible, and a singularity in the shape of a ring. Your intuition is correct that during a merger it would be weirder still.
https://en.wikipedia.org/wiki/Kerr_metric
https://arxiv.org/pdf/0706.0622
https://en.wikipedia.org/wiki/Ergosphere
https://en.wikipedia.org/wiki/Cauchy_horizon
Edit: Updated the bit about about horizons as I research a bit more. It's complicated, and I'm still not positive I have it exactly right, but I think it's now as good as I can get it.
Simulation: https://www.youtube.com/watch?v=Tr1zDVbSjTM
What kind of timeframe does that animation happen over?
Everything is a fluid in the end and at scale right??
No matter how chaotic the merger looks, the event horizon must asymptotically become either spherical (Schwarzschild) or oblate (Kerr). The mass distribution inside doesn’t change this, general relativity doesn’t allow static “lumpy” horizons.
It’s wild how much happens in those milliseconds though. Numerical relativity papers like the one you shared from arxiv.org show the horizon “sloshing” before it stabilizes.
When water sloshes it ejects small droplets. Can the event horizon eject black hole droplets during a violent merger event?
It cannot. The event horizon by definition prevents mass and energy from leaving (ignoring the exception of Hawking radiation here). I'm assuming your "black hole droplet" would be a tiny black hole? But if you could remove a little chunk from the black hole then you've effectively taken mass out of it, which is impossible.
It is even the case that once two black holes have overlapping event horizons (so they "touch" in a way) they can't stop touching. So two black holes can zip past one another at a small distance, but if they high-five they can't stop merging.
Is it even sensible to talk about a "mass distribution" inside of an event horizon?
Sure, especially consider if singularities are not real. Then what's inside the event horizon is just some bunch of unknown material in some actual shape. Why wouldn't it be?
If singularities are real...same thing but more boring answer maybe? (the distribution just being: in the center).
> Why wouldn't it be?
Because the whole concept of "shape" assumes properties of space that might not apply inside an event horizon?
There’s no reason to expect that the properties of space are different inside the event horizon than outside. Of course the direction of time turns sharply as you go inside, but otherwise space is just space.
You only get an asymmetric black hole during the milliseconds of a merger. And that asymmetry is entirely due to the mass distribution inside the black hole. The black hole only becomes spherical again once the singularities have merged. Or in the more common case of rotating black holes, they only become properly oblate again once their ringularities have merged. Either way it happens quite quickly.
> the direction of time turns sharply as you go inside
Yeah, that's what I meant. It's hard for me to reconcile the concepts of "the direction of time turns sharply" with "space is just space".
I am certainly no physicist but I remember coming across academic papers in the past speculating about exactly your question. I recall one theorized about singularities being hollow with all of the mass (err was it space? spacetime?) compacted down into 2 dimensions on a shell at the surface (at least IIUC, which I probably didn't).
I think that concept might fit with the infinite time dilation preventing a merger from ever actually occurring? I'd be curious how that might differ for matter that's already inside when the critical mass is reached. (I'd also be curious to know all the creative and wacky ways in which I got the above completely wrong given that's just about inevitable.)
Mass curves space. All mass curves space all the time. You are bending the fabric of spacetime even now! Don’t try to deny it!
What does curvature mean? It means that the direction of time’s arrow is different in different places. To an observer outside of a large gravitational field, events inside the field appear to move more slowly than they would have outside of it. Black holes merely take this to an extreme. To an observer far from a black hole, a clock entering the black hole appears to slow down and finally _stop_ as it crosses the event horizon¹. But simultaneously an observer traveling with the clock observes something different. They see everything outside the black hole slow down and stop instead, while they continue to coast smoothly along. They notice nothing strange at the horizon itself; it is simply empty space with weird visuals in the distance.
This almost seems like a paradox, since the two observers each believe that the other’s clock has stopped. The reason why it’s not a paradox is that the space around the black hole is strongly curved, so strongly that the axis of time swaps place with one direction of space. At the horizon the axis of time flips over and points down into the black hole. The distant observer sees time stop because time is now edge–on, as it were. The observer falling into the black hole notices nothing weird near themselves, because both time and space still exist. Only the images of distant objects show any evidence of curvature. But the falling observer is doomed, for their own time axis now points at the singularity. Their timeline now ends abruptly, while the timeline of the distant observer extends potentially a vigintillion years.
For some edutainment on the subject, I recommend The Science Asylum. He’s done a bunch of videos on gravity and relativity, but here are two in particular:
¹ There are other effects too. The image of the clock _lingers_ on the horizon forever, since for it time has apparently stopped. But the redshift increases to infinity too, as the gravitational well becomes steeper, so no matter what wavelengths we observe in the image of the clock fades away beyond sight. Worse, the tidal forces caused by a real stellar–mass black hole will tear apart solid objects into a stream of plasma, even small objects. So the hypothetical black hole in our thought experiment must be very large indeed, to minimize the tidal forces enough that the clock survives the trip to the horizon intact and functional. And it can't be rotating either, since the rotation causes its own weirdness. This is the spherical cow of black holes.Eh, space inside or outside the horizon is only different in so far as to whether it can reach our timelike infinity. Locally you cannot even tell where any horizon might be (just look at a small patch of a Penrose diagram near a horizon), they are very much something related to global properties of the spacetime. In particular it's not problematic to talk about some extended volume in spacetime occupied by mass, as long as the divergence of the stress energy tensor is 0.
The point where our notions of geometry would break down would be near the singularity, not near the horizon, and we don't even know if a volume enclosed by a horizon (i.e. anything you might call a black hole) necessarily has a singularity inside, it's just that our simple mathematical models all assume one.
Because having some observational knowledge of the inside is impossible, in a sense it doesn’t matter.
Could you (or anyone) tell what the radius of the ring singularity is, in terms of mass and angular momentum? I haven't been able to find that.
The math seems to suggest R=a, or simply the spin in terms of length. It's certainly an oversimplification, as the answer will depend on the choice of metric.
Here's the best resources I've been able to find on the question. Roy Kerr himself responded to the Quora question:
> There is no Newtonian singularity at the Center of the earth and there is no singularity inside a rotating black hole. The ring singularity is imaginary. It only exists in my solution because it contains no actual matter. When a star collapses into a black hole it keeps shrinking until the centrifugal force stabilizes it. The event shell forms between the star and the outside. In 57 years no one has actually proved that a singularity forms inside, and that includes Penrose. instead, he proved that there is a light ray of finite affine length. This follows from the “hairy ball theorem”.
The stack overflow answer seems to describe the problem in terms I can better understand:
> It seems unlikely to me that you're going to be able to formulate a notion of diameter that makes sense here. Putting aside all questions of the metric's misbehavior at the ring singularity, there is the question of what spacelike path you want to integrate along. For the notion of a diameter to make sense, there would have to be some preferred path. Outside the horizon of a Schwarzschild black hole, we have a preferred stationary observer at any given point, and therefore there is a preferred radial direction that is orthogonal to that observer's world-line. But this doesn't work here.
https://physics.stackexchange.com/questions/471419/metric-di...
https://www.quora.com/What-is-the-typical-diameter-roughly-o...
It is difficult to talk about the shape of the event horizon because the ordinary definition of a sphere is "surface where all points are equidistant from a given point" is already complex in a differentiable manifold, but even more so when the distance is infinite because of a singularity (or the point doesn't exist/isn't unique because of geodesic structure). So you switch to a definition of "surface of constant scalar curvature with the topology of a sphere", the topology being important to distinguish it from a plane and a hyperboloid.
From there, I haven't personally done or seen the calculations of the shape of the horizon for Kerr or merging black holes, but my intuition is that it would be indeed peanut shaped for a merger (there are likely some saddle points). The coordinate shape certainly is but you can choose coordinates so that a Schwarzschild black hole is a coordinate peanut so coordinates aren't very meaningful.
Here is an animation from MIT/CalTech of what a merger looks like:
https://youtu.be/1agm33iEAuo
From our perspective there is no event horizon since the collapsing star has not reached the black hole state. In fact it takes infinite amount of time from the point of view of an external observer for the event horizon to form.
In almost all situations it does matter as the collapsing star will behave as it is a black hole. But for the merge of black holes it is significant as it allows to release energy as there is no event horizon.
Does the black hole's spin deform the event horizon?
I think so?
https://archive.ph/VrzwW
Edit: "The Kerr metric also predicts the existence of an inner and outer event horizon, with the shape of these horizons being oblate rather than perfectly spherical due to the rotation."
Kind of. Because the black hole drags space around with it you need to go faster near the ‘equator’ than the poles just to stand still. So the event horizon is fatter at the equator.
I'm no physicist but what I've learned on the internet through osmosis, I'd wager that black holes aren't spherical per-se, but they appear sphere-like to us dimensionally challenged beings. It's more like a manifold (mobius-gate? not a mobius surface), that changes your spatial directions to parallel temporal directions to spatial ones all leading to the singularity.
But black holes are incredibly efficient at radiating away asymmetries via gravitational waves
Is there a "mass distribution" inside? AFAIK a black hole is a singularity which means it's mass is in one (infinitely small) point.
I wonder what would happen if one black hole shot through another one at high relativistic velocity, instead of spiralling towards one another.
The thing is that the spacetime around blackholes get curved to the actual extremes.
When we imagine flying "at nearly the speed of light" towards something thats traveling the same speed towards you, we tend to imagine a collision at high speeds.
But for blackholes that turn space into time and time into space, they can see the other blackhole slowing to a complete stop as its about to touch. Or it can look differently, it all depends on the position and speed of an observer.
We cant even agree on the basics like: "It doesnt matter how it looks, but they must collide", since if we look at something falling into a blackhole (which I pressume could be another blackhole just as well), we see it slow towards 0 at the edge and fade away in redshift instead of seeing it actually fall trough.
Its just all very weird and unintuitive stuff.
They would merge and produce a black hole with the sum of their momentums
Because nothing can ever leave the event horizon black holes are essentially perfectly sticky.
What if the collision was only a grazing one, not head on?
Would they still fully merge, or might you get a mass exchange between them? Or even a smaller black hole spun off?
To answer my own question, some lay research shows it seems it is technically possible for them not to merge if only a tiny portion of their apparent event horizons merge and for only very briefly.
But this is because of a distinction between the Apparent Horizon [1] (which is coordinate-dependent) and the true global event horizon. So they appear to briefly merge but no true global event horizon forms to encompass both. I think!
[1] https://physics.stackexchange.com/questions/38721/what-is-th...
So, if two black holes, each with mass M, were moving at nearly the speed of light and collided head-on (resulting in a final velocity of zero), what would happen to all that momentum? Would the resulting black hole have a mass greater than 2M? If so, how and why would this occur?
I think I'm going to answer my own question by saying both momentum and energy are conserved. The momentum of the entire system was zero before and after the collision. Energy must also be conserved, and since the final object is at rest, all the kinetic energy gets converted into rest mass energy, minus what is radiated away as gravitational waves.
Correct. If you're curious about the 'essence' of what black holes are I actually just did a write-up on them which you can find here: https://photonlines.substack.com/p/an-intuitive-guide-to-bla...
Thanks. Little typo "Let’s inflate Earth once again to its regular size and see what impact placing a 10 kg weight on it has." Should be 1kg.
Thank you - I will correct the mistake!
I'm not a physicist, but I took a class on special relativity in college, and I still remember some of it ... If I'm remembering it right, we still have conservation of momentum and energy in special relativity, with the caveat that these are defined differently than in classical mechanics. Specifically, E = γmc^2 and p = mvγ, where γ = 1 / sqrt(1 - v^2/c^2) and m is the invariant mass (aka the "rest mass"). [1] Note that when v=0 (so γ=1), this equation for momentum is the same as the classical p=mv, which is generally a good approximation when v << c.
So, using those relativistic definitions for energy and momentum, I think you're exactly right, at least up to the part about "since the final object is at rest". However:
- As I understand it, invariant mass, aka "rest mass" (which is equivalent to "rest energy", aka "rest mass energy"), is invariant, and it's the same before and after the collision, so the kinetic energy doesn't get "converted into rest mass energy". Rather, if the final object is at rest, then all of its kinetic energy has been radiated away; kinetic energy (E_K) is is total energy (E) minus rest energy (E_0 = mc^2, where m is invariant mass)
- I have no idea whether gravitational waves are the only way for the kinetic energy to be radiated away. I imagine other forms of energy could also be emitted.
- In order to know that the final object is at rest/has no kinetic energy (in an inertial frame), I worry that we might need to have specified more in the original question. In particular, I don't know how to handle spin. (I know that black holes have some concept of "spin", but I don't know if this is like rotational spin, or more like quantum mechanical spin, or something else, and I don't know how it figures into the black holes' total energy.) If we change the original question to say that the black holes are not spinning, then I think we can ignore this (since the collision is head-on).
[1]: https://en.wikipedia.org/wiki/Mass_in_special_relativity#Rel...
To reiterate, I'm not a physicist. I may be off base here, but that's my understanding.
Energy and momentum are always conserved in EVERY physical process. We can distinguish three types of collisions: “sticky” ones, in which the kinetic energy decreases (typically, it is converted into heat); “explosive” ones, where the kinetic energy increases; and elastic ones, in which the kinetic energy is conserved. Since the total energy (rest plus kinetic) is always conserved, it follows that rest energy (and hence also mass) increases in a sticky collision, decreases in an explosive collision, and is unchanged in an elastic collision. The resulting black hole in other words would have way more of a mass than 2M since you're talking about a 'sticky' collision in the above instance. You can see an example of why this is in Griffiths' text (Introduction to Elementary Particles (which I highly recommend)) -- page 101 contains a great example of what happens to the mass of particles in 'sticky' collisions: https://www.hlevkin.com/hlevkin/90MathPhysBioBooks/Physics/Q...
> Energy and momentum are always conserved in EVERY physical process.
Veritasium recently claimed otherwise https://www.youtube.com/watch?v=lcjdwSY2AzM
That is about something entirely different. It more or less just says that energy might be lost if you have a flux towards infinity. It does not in any way claim e.g. that the divergence of the stress energy tensor is non-zero (which would be how I think most people would interpret energy/momentum conservation).
My hunch is they would briefly pancake and much of the mass/energy contribution from their initial velocities would dissipate as incredibly high amplitude gravitational waves from the ring-down.
They would cancel each other out and disappear, like a snake eating its own tail.
It would create a universe, obviously. First all the mass would attempt being squished at a singularity. WHILE the squishing continues, the first-in-line stuff would've already started to explode back-out inside the event horizon. From the inside viewpoint, this looks like the big bang. Once all the mass from the two black holes collide and loose momentum, the inside-universe no longer expands as fast. Things wobble a bit as all this happens, creating tangles and non-homogeneity. Could be caused by initial Planck-scale uncertainties even when having a perfect head-on collision.
> Because nothing can ever leave the event horizon black holes are essentially perfectly sticky.
If Hawking radiation turns out to be non existent, yes.
Also, we don't know if it's possible to 'crack' open a black hole. If anything, another black hole might be the perfect instrument for doing this.
Hawking radiation occurs because black holes are sticky ‼
Huh nice analogy
When you say cracking open a black hole do you mean cracking the event horizon to form a naked singularity?
The answer would likely be worth a Nobel prize or two.
> black holes are essentially perfectly sticky
Black Hole brand adhesive: when you absolutely, positively need something stuck down for eternity.
The escape velocity from inside the event horizon is faster than the speed of light, which is the highest possible speed in the universe.
So black holes cannot approach each other faster than the speed of light. And if their trajectories intersect perfectly, they won’t be able to escape each other’s gravity.
A black hole can’t pass “through” another black hole like two bullets hitting each other. More like two incredibly strong magnets hitting each other in midair.
Too bad we can't set up a cosmic particle accelerator to test this!
Kind of amazing that LIGO/Virgo/KAGRA can even detect and decode something that extreme
What is the budget outlook for LIGO?
Was the budget cut in the BBB passage last week?
What happens when black holes collide? Does one black hole “consume” the other? Do they become a larger black hole? Does it get more dense or just larger?
They become a larger black hole, mostly conserving mass, minus a few percent to gravitational waves. However, their mass is proportional to their radius, not volume, so it gets LESS dense. If you laid out a bunch of black holes in a line, just barely not touching, and let them merge, suddenly, the whole sphere of space enclosing the line becomes black hole. It also turns out that a black hole with the mass of the universe would have a volume about the size of the universe.
> turns out that a black hole with the mass of the universe would have a volume about the size of the universe
Mass and energy.
Is that intended to be a correction? (I don't think the original statement needs correcting, other than by replacing "universe" with "observable universe" in both places.)
Up until the universe was around a few billion years old, its Schwarzchild radius would have been larger than even the co-moving (not just observable) universe's radius, but the initial momentum from the big bang was high enough to prevent collapse.
That sounds suspiciously like "they were inside a region with enough mass to form an event horizon, but they escaped because they had enough momentum", which in turn sounds like "we can escape from inside an event horizon if we just move fast enough". Can you explain how that's not what you're saying?
I wish I had a straightforward answer to that. I'm sure the answer is some combination of cosmic inflation and dark energy, but by all means it appears the early universe either narrowly escaped, or simply is a black hole, that singularities are a flawed concept, that nothing is escaping the universe, and we are all stuck moving forward in time, and that the infinite future is the singularity.
I don't have an answer either. But in my amateur opinion, of the available options, I lean toward "is a black hole". If all the mass we can see adds up to a black hole the size of what we can seen, then if you add all the stuff outside the light cone, it should add up to enough mass to make a black hole radius that includes the distance out to there.
But that leaves us with black holes forming inside a black hole, which I have absolutely no idea what to do with.
Mass alone doesn’t do it. You need energy, namely the CMB, to push the observable universe close to its Schwarzschild limits.
Ohh, I see, you mean "mass" should have been "mass and energy" rather than e.g. that (mass,volume) should have been replaced by (mass,energy) or something.
I confess I just ... take it for granted in this kind of context that "mass" or "energy" or "mass+energy" all mean the same thing. Someone who wants to refer just to the total amount of matter will say something like "the total mass of the matter in the universe".
It's commonplace for physicists to write just "mass" when talking about this sort of thing. E.g.,
P T Landsberg, "Mass scales and the cosmological coincidences", Annalen der Physik, https://onlinelibrary.wiley.com/doi/10.1002/andp.19844960203:
"Theories involving the parameters h, c, G, H (in a usual notation) are considered. A huge ratio of 10^120 of the mass of the universe (m_u) to the smallest determinable mass m_0 in the period since the big bang occurs in such theories."
(Not cherry-picked; I went to the Wikipedia article on "Black hole cosmology", noted that it just says "mass" rather than "mass-energy" or whatever, and followed the link in the attached footnote. Also, so far as I know, not crankery; Landsberg was an eminent physicist.)
Is that true though?
Can't we generalize to say that we observe that black holes have a similar density (which is to say, proportion of mass to volume) any sample of the observable universe sufficiently large as to be roughly uniform?
In other words, doesn't this observation scale both down (to parts of the universe) and up (beyond the cosmological horizon, presuming that the rough uniformity in density persists), at least for any universe measured in euclidian terms?
It's very possible that I'm wrong here, and I'd love to be corrected.
...I also think we have to acknowledge that "similarly" is doing a fair bit of work here, as we're not accounting for rate of expansion - is that correct?
>> just barely not touching
Which part of them is barely not touching?
Maybe I should've linked my toy simulator in my initial comment.
https://cybersystems.dev/gtc/gtc.html
BTW, the php in /chat2 seems to be broken, if you didn't know already. Great simulation, too.
Thanks, I was kinda curious why it wasn't full of spam. it's running on a super neglected rpi, really need to wipe it and spend a month refreshing myself on basic webhosting stuff
The events horizon.
Or in other words, black holes mergers conserve their total radius, not volume as one would get with normal matter.
The event horizons.
In cosmological terms, what is barely not touching? Is that distance measured in meters, kilometers, AUs, lightyears, parsecs?
In terms of creating a row of black holes where the space between each black hole is small relative to the size of the event horizon of each.
> minus a few percent to gravitational waves
They actually convert up to 42% of their mass into energy, mostly radiation
https://youtu.be/t-O-Qdh7VvQ
For normal matter inspiraling, yes, but a black hole which is falling into a black hole doesn't get to glow in gamma rays to try to escape :) they can only lose mass/energy by making splashes in spacetime itself (or hawking radiation)
I think this is over their lifetime, not when they merge?
They become a more massive one. The volume of a black hole (assuming you're measuring at the event horizon) is determined only by its mass, so the final density is the same as you'd get for any other black hole of that mass regardless of how it came to be.
I don't know how to address the "consume" question. If you were pulling on a piece of fabric and two tears in it grew until they met each other to become one tear... would you say that the larger one consumed the smaller?
> the "consume" question
My guess is that in some popular depictions black holes are like holes, and things fall in the holes, and even a small black hole can possible fall inside a bigger hole.
A better image is too drops of water on a glass, add some black ink for bonus realism. They merge into a bigger drop. Except, obviously black holes are not filled with water. And the "average density" of the new black hole is smaller then the "average density" of both original black holes, unlike the density of water drops on a glass. So don't take this image too literaly.
(There are some problems to define the "density" of a black hole, but let's ignore all of them.)
> The volume of a black hole (assuming you're measuring at the event horizon) is determined only by its mass, so the final density is the same as you'd get for any other black hole of that mass regardless of how it came to be.
Wait, really? So if you had a super massive disk that was just 1 electron away from having enough mass to become a black hole... and then an electron popped into existence due to quantum randomness... then it would become a sphere instantly? Wouldn't that violate the speed of light or something?
> then it would become a sphere instantly
Event horizons are non-physical. Better to think of it as "then a spherical event horizon would become apparent." When the mass within a given black-hole-shaped volume (spherical for non-rotating mass) is "one electron short" of being a black hole, then one can define a surface in the shape of the (future) black hole where the escape velocity is /just/ below the speed of light. In practice, all light emitted within that volume will already be captured by the mass, unless it's perfectly perpendicular to the (future) event horizon. When that extra electron is added, it becomes true that the escape velocity at that same surface is now the speed of light -- the definition of event horizon. But nothing needs to "form" to make this true.
It's the https://en.wikipedia.org/wiki/No-hair_theorem , but it only applies after a while, not instantly.
Your disk will emit a lot of gravitational on electromagnetic radiation, and after a while it will be a nice sphere. (Unless it's rotating and it will be a nice somewhat-elipsoidal ball.)
---
> and then an electron popped into existence due to quantum randomness
I feel there is a huge can of worms of technical problems in this sentence that nobody know how to solve for now. Just in case replace the quantum randomness with a moron with a broken CRT used as an electron cannon.
> and after a while it will be a nice sphere
Time doesn't exist for black holes, so "after a while" is not something you can say about them.
Simulations linked in others comment:
https://www.youtube.com/watch?v=Tr1zDVbSjTM
https://www.youtube.com/watch?v=1agm33iEAuo
The second one is much more correct, notice how it freezes before they actually merge because they time dilate out to infinity.
If they actually froze just before the merge, they will be peanut shaped like in the video.
I'm not sure if we can measure the shape of black holes, but I'm sure everyone think they are spheres with a slight deformation due to rotation.
The algorithm choose this for me https://www.youtube.com/watch?v=fKgQYOlpxmo
The analogy I like goes something like this. Imagine you're paddling in a canoe on the river. You approach a waterfall. If you do nothing you'll get consumed by the waterfall. So you try to paddle away from the waterfall, but as you get closer to the edge of the waterfall, the current gets stronger.
The event horizon is the imaginary line across the river which once passed, even if you paddle as quickly as you can, you won't be able to get away from the waterfall. Once you pass that line, you're bound to reach the waterfall eventually.
Now, thanks to Maxwell and Einstein, we know there's a maximum speed that anyone can paddle, the speed of light, and so we define the event horizon to be relative to this speed.
You can calculate the event horizon for just about anything. The main difference between a black hole and everything else, is that for a black hole the event horizon is larger than the object itself.
For example, the event horizon of a neutron star with a mass of 1.4 solar masses and a radius of 10km is about 4.1 km, well inside the neutron star. Thus you don't get the "black hole effect", since once you pass the surface of the neutron star the matter above you pulls you away from the center.
The river analogy is actually not far off what they try to use as an analog for testing black hole predictions, effectively a large water tank with a drain hole. Sixty Symbols did a video on this way back[1], and this thesis[2] goes into the details. Some are going beyond water using liquid helium to simulate quantum black holes this way[3].
[1]: https://www.youtube.com/watch?v=kOnoYQchHFw
[2]: https://arxiv.org/abs/2009.02133
[3]: https://pirsa.org/25010083
Long before your disc neared the mass where it would form an event horizon, the matter it's made of would collapse into neutron star material, which would form a sphere.
Perhaps if it were exceptionally wide the whole disc wouldn't collapse. Maybe only the parts near it's center. In that case you'd end up with a large ring around a neutron star. Add a bit more mass and maybe it's now a ring around a black hole. The gravity of the ring might distort the event horizon in some way, I'm not sure quite how, but probably its possible to get a non-spherical hole in situations where the objects distorting the shape are still in the universe.
But as for the matter lost into the hole, it's gone. If the hole were to retain some shape based on what's "inside" of it, that would be the kind of information leak that the laws of physics do not permit.
That electron would take an infinite amount of time to reach the edge, since time dilates to infinity with gravity that strong.
> a sphere instantly
The concept of instantly doesn't work with time dilation like this. What you see will be different depending on if you are also falling in, or if you are far away.
I think the GP meant “merge”
What happens inside cannot be known.
As I understand it, black holes are defined by three quantities: mass, spin, and charge.
I'm assuming that these quantities will be additive post-merger.
Edit: "The black holes appear to be spinning very rapidly—near the limit allowed by Einstein's theory of general relativity."
Perhaps the additive spin becomes asymptotic. Alternately, the gravitational waves might have departed with the energy of the excess spin.
My understanding is they just spiral into each other forever.
From our point of view nothing can actually fall into a black hole, instead it time dilates into nothing. "It is true that objects that encounter the event horizon of a black hole would appear “frozen” in time"[1]
So we would never actually see the black holes merge. In fact I'm not clear how a black hole can even form in the first place, since it would take an infinite amount of time to do so (again, from our POV).
(And yes, I know that from the POV of the falling object, they just fall in like normal. But that doesn't help us, because we'll never see it.)
[1] https://public.nrao.edu/ask/does-an-observer-see-objects-fro...
This is true, but it's not an observable distinction. It's true that in some sense those two black holes "haven't yet collided", but at this point they're well past the point of last observability and have now red shifted and time dilated into the invisible background. All the interesting stuff happens before that.
My basic understanding is that they combine, basically you just add the masses together. That increased mass then means more gravity, so the event horizon is pushed further out.
Chirps or it didn't happen
I wonder how the singularities would merge with each other.
We can't REALLY answer questions about what's inside the event horizon, but some real work has been done on what BH mergers look like, though even that as I understand, is extremely difficult model.
https://m.youtube.com/watch?v=5AkT4bPk-00
These kinds of simulations inherently cannot model the singularity accurately whatsoever. At the singularity, the numerical technique used becomes knowingly invalid
In fact, the entire interior of the event horizon is actually physically invalid in these simulations. The formalisms used trap the errors inside the event horizon, as the errors turn out to be strictly causal. And because of that, theoretically they can't escape
Of course that analysis breaks down in the face of discretisation, so errors tend to leak out a bit under low resolutions, so you have to handle things pretty careful. Either way, you shouldn't draw any conclusions about the interior
Source: I've done a lot of these simulations
What are the waves of gradient colors, gravity?
I'd guess its the weyl scalar w4, which is generally used to extract gravitational waves
[dupe] https://news.ycombinator.com/item?id=44555220
Boring press release without any real details. I wish the paper would trend not an empty press release announcing the announcement.
Everything in the universe is massive because we are just so small. Everywhere but within the confines of our solar system, calling something massive is a meaningless endeavour, it’s so big nobody has any idea how to appreciate it, and then there is always going to be something bigger which makes that black hole look tiny
so I hate to have to ask this but must
is the space version of LIGO, known as LISA (and will be far more sensitive)
now doomed? because of the "savings" by DOGE?
https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Ant...
This is a project by ESA, it's not affected by DOGE
https://www.esa.int/Science_Exploration/Space_Science/LISA/C...
LISA is (was?) listed as a joint NASA-ESA project
Both LISA and LIGO II were deleted from the last Congressional budget
https://lisa.nasa.gov/
https://bigthink.com/starts-with-a-bang/ligo-heaviest-black-...
even the "sound" is spooky
https://www.youtube.com/embed/QyDcTbR-kEA
In case it's not clear, that 'chirp' is exactly what we would hear if the merger was powerful enough to actually be detectable by our ears. It's the vibration induced in the final moments and the frequency is the speed at which the blackholes are orbiting each other before they merge. Things the size of multiples of our Sun dancing around each other a thousand times per second. It's insane to me.
When I read 'news' like that, I 'compare' myself to the thing. And then I think how this 'thing' can swallow me, everyone around me, everything as far as the eye can see (thank you light pollution, we can only see the moon and perhaps 5-6 more 'things' out there (ffs!)) and then we will be 'no more'.
But then I use the voice of Djimon Hounsou and the quote from the Gladiator "but not just yet".
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