Is the universe being swallowed up by black holes?

[Project Orion]

Is the galaxy just an accretion disc around a supermassive black hole? All the larger galaxies so far studied seem to be orbiting supermassive black holes. Is the fate of the universe to be eaten?

[grant hutchison]

Is the galaxy just an accretion disc around a supermassive black hole? All the larger galaxies so far studied seem to be orbiting supermassive black holes. Is the fate of the universe to be eaten?Galaxies aren't, in general, accreting on to their central black holes: most stars are in stable orbits that never come anywhere near the central black hole.

Grant Hutchison

[Jens]

Galaxies aren't, in general, accreting on to their central black holes: most stars are in stable orbits that never come anywhere near the central black hole.


I assume the OP is about the very, very, very long-run. I think he is probably imagining that the black holes will slowly grow as they accrete matter. I guess the question of black hole evaporation would also come into this, so I don't really know how to answer.

By the way, why does "accrete" get tagged as a bad spelling. Accretion is OK, but not the verb?

[Cougar]

I assume the OP is about the very, very, very long-run.

That's right. It's hard to imagine just how long of a run the OP scenario takes. According to Sean Carroll in From Eternity to Here, occasionally a couple of stars interact such that one is ejected from a galaxy. Thus the galaxy loses some energy. So perhaps billions or more times the current age of the universe, there are just a lot of black holes. Then, as you say, Jens, after another probably billion2 times the current age of the universe, Hawking radiation takes over and reduces the universe to a thin wisp of next to nothing. That's assuming there isn't a vacuum metastability event (http://en.wikipedia.org/wiki/False_vacuum) that happens first. Or a big rip (http://en.wikipedia.org/wiki/Big_Rip).

[kleindoofy]

... I think he is probably imagining that the black holes will slowly grow as they accrete matter. ...
But even if they do grow, the net gravity stays the same, so why would that matter?

[caveman1917]

Wouldn't, over very large timescales, the orbits of the stars (and other stuff) decay due to gravitational radiation?
Then it would seem galaxies are bound to 'collapse' into black holes. Disregarding Hawking radiation that is.

[antoniseb]

At some distance from the central black hole, the expansion of the universe will exceed whatever factors draw stars toward the center, preventing some/most matter from being consumed.
I haven't done ANY calculations on this, but it seems likely to be true.

[kleindoofy]

... most stars are in stable orbits that never come anywhere near the central black hole. ...
Speaking of the long run, I suppose that, even disregarding disturbance factors, no orbit is actually perfectly stable, i.e. even in the stablest of orbits the initial velocity will either be slightly above or below the perfect value. The orbiting body will move ever so slowly either towards or away from the central body, as the Moon is moving away from the Earth.

[Cougar]

Speaking of the long run, I suppose that, even disregarding disturbance factors, no orbit is actually perfectly stable, i.e. even in the stablest of orbits the initial velocity will either be slightly above or below the perfect value. The orbiting body will move ever so slowly either towards or away from the central body, as the Moon is moving away from the Earth.

Don't think so. I'm thinking a little more or less velocity will just change the eccentricity of the elliptical orbit.Then again, even the orbital motions of the planets in the solar system are chaotic. (Laskar 2003) (http://www.imcce.fr/Equipes/ASD/preprints/prep.2003/th2002_laskar.pdf)

[grant hutchison]

Speaking of the long run, I suppose that, even disregarding disturbance factors, no orbit is actually perfectly stable, i.e. even in the stablest of orbits the initial velocity will either be slightly above or below the perfect value. The orbiting body will move ever so slowly either towards or away from the central body, as the Moon is moving away from the Earth.That sort of evolution would require orbiting stars to raise tides on the black hole, which I think is impossible.

Grant Hutchison

[Frog march]

If nothing crossed any event horizon(ie no event horizon forms), and all you had was infalling matter, then you could raise a tide.

[grant hutchison]

If nothing crossed any event horizon(ie no event horizon forms), and all you had was infalling matter, then you could raise a tide.To quote the Spartans: "If."

Grant Hutchison

[Cougar]

If nothing crossed any event horizon(ie no event horizon forms)....

Similarly, if there was no universe, we wouldn't be considering the OP's question.

[kleindoofy]

... I'm thinking a little more or less velocity will just change the eccentricity of the elliptical orbit. ...

That sort of evolution would require orbiting stars to raise tides on the black hole, which I think is impossible. ...
Ah, ok.

Assuming that neither of you is a NASA pansy who is being paid by the government to fool us, enslave us, and steal our money, I'll go with that. ;)

[xylophobe]

That sort of evolution would require orbiting stars to raise tides on the black hole, which I think is impossible.

Grant Hutchison

What about tides in the gravitational field of the black hole - is such a thing possible?

Besides, even if the blackhole can not have tides then the orbiting bodies certainly can have tides that effect their orbit.

[phunk]

Or tides in the accretion disk of the black hole. But I can't imagine those being significant to most of the stars in the galaxy, even on huge timescales

[caveman1917]

That sort of evolution would require orbiting stars to raise tides on the black hole, which I think is impossible.

Grant Hutchison

Are you sure about this? It seems to me that should be possible.
If i remember correctly, simulations of the merger of two black holes showed distortions in the EH consistent with what would be tide-raising in a less violent scenario.

[Andrew D]

Are you sure about this? It seems to me that should be possible.
If i remember correctly, simulations of the merger of two black holes showed distortions in the EH consistent with what would be tide-raising in a less violent scenario.

It seems to me that it shouldn't be, the horizon is a geometric phenomena with a radius that's a function of the mass within the singularity, which is point like, so they will be spherical until the merger occurs.

[caveman1917]

It seems to me that it shouldn't be, the horizon is a geometric phenomena with a radius that's a function of the mass within the singularity, which is point like, so they will be spherical until the merger occurs.

The EH is an effect of the curvature of some "patch" of spacetime. When looking at one BH it will be spherical, since the source of the curvature will be point like. However when throwing other "stuff" into the mix, that might change i would think.

[Andrew D]

The EH is an effect of the curvature of some "patch" of spacetime. When looking at one BH it will be spherical, since the source of the curvature will be point like. However when throwing other "stuff" into the mix, that might change i would think.

Can you elucidate this "stuff"?

[caveman1917]

I meant anything that will have a gravitational effect, though probably it would be more pronounced with high mass objects, say as in putting another black hole next to the first one.

I don't know if it would raise tides, but i have not seen anything contrary to that expectation - so i would be interested to know why one way or the other.

[WayneFrancis]

I haven't done the maths but if anything 2 black holes orbiting each other would cause a dimple in their event horizons not case the EH to bubble out. Effectively what the BHs are doing is negating some of the gravitational force of the other BH.

[caveman1917]

If it causes a dimple, might that be a mechanism for orbital decay?
It seems it would cause a dimple on the near side, but a bulge on the far side (where they work 'together').
We'll probably need someone familiar with the maths, the whole thing is probably highly non-linear around that case and analogies might fail.

[invisible]

The universe is expanding at an increasing rate. So how can black holes eat everything. Only the more massive stars out there will become black holes. I imagine the black holes will eat each other and dust will inherit the universe.

[Andrew D]

Wayne-

Is the "dimple" a tidal effect?

Invisible-

Welcome to BAUT, and the universe is expanding, but objects that are gravitationally bound, like stars in a galaxy in reach of the central clack hole, don't expand. At that range, gravity is stronger than the force that causes expansion. So, it's easy to imagine a distant future in which much of the matter in the universe is contained in massive black holes that are moving away from eachother.

[invisible]

Galaxies sometimes collide and merge. I know that when black holes collide they become a bigger black hole. I was just thinking how galactic star swallowers like the one at the centre of the milky way could merge in this fashion. creating stupendously massive gravity wells. I suppose there is no theoretical limit to how large a black hole might be. Do we know which came first? Galaxies or black holes?

[grant hutchison]

Are you sure about this? It seems to me that should be possible.
If i remember correctly, simulations of the merger of two black holes showed distortions in the EH consistent with what would be tide-raising in a less violent scenario.Yes, and a massive object in a tight orbit will raise a little bulge in the EH, too. But my point is that there's no mass being raised inside that bulge: it simply marks off the region of spacetime in which photons are doomed to hit the singularity. The EH bulge also doesn't lag because of viscous forces or the rotation of the black hole: it seems like a very different beast from a conventional tidal bulge.

(It's a bulge, not a dimple. What determines photon escape is the gravitational potential, not the net force. An object trapped between two converging black holes may experience a cancellation of forces, to some extent, but it's enmired in the potential wells of both black holes. Simulations of colliding holes show the event horizons reaching out towards each other as their gravitational potential adds in the region between the two holes.)

ETA: Some illustrations (http://www.psc.edu/research/graphics/gallery/winicour.php) of black hole mergers.

Grant Hutchison

[Jeff Root]

I recall that the filesize of the animation Grant linked to is absurdly
large, at least considering how crude it is. I drastically reduced the
size without affecting the quality in a fit of obsessive-compulsivity:

http://www.freemars.org/jeff2/winicour_A_jsr.gif

-- Jeff, in Minneapolis

[caveman1917]

Yes, and a massive object in a tight orbit will raise a little bulge in the EH, too. But my point is that there's no mass being raised inside that bulge: it simply marks off the region of spacetime in which photons are doomed to hit the singularity. The EH bulge also doesn't lag because of viscous forces or the rotation of the black hole: it seems like a very different beast from a conventional tidal bulge.

(It's a bulge, not a dimple. What determines photon escape is the gravitational potential, not the net force. An object trapped between two converging black holes may experience a cancellation of forces, to some extent, but it's enmired in the potential wells of both black holes. Simulations of colliding holes show the event horizons reaching out towards each other as their gravitational potential adds in the region between the two holes.)

ETA: Some illustrations (http://www.psc.edu/research/graphics/gallery/winicour.php) of black hole mergers.

Grant Hutchison

Thanks for the explanation.

[neilzero]

Let's assume that 3% of the matter in the Universe is presently in blackholes and that will be 3.000004% in another 13.7 billion years. At he end of the next 13.7 billion years the matter in black holes will be 3.000006% = decreasing gain due to the reduced density, due to expansion and less matter not trapped yet. In about one google years, the average evaporation of black holes may exceed the capture rate (if black holes evaporate). In much less than a google years lots of other stuff will likely happen, so the prediction is likely invalid.
Even if black holes have captured 99.999999% of the matter in the Universe, the last tiny bit will take almost forever to cature due to 99.999999999% of the cubic light years having no blackholes. Neil

[Cougar]

Let's assume that 3% of the matter in the Universe is presently in blackholes and that will be 3.000004% in another 13.7 billion years. At he end of the next 13.7 billion years the matter in black holes will be 3.000006% = decreasing gain due to the reduced density, due to expansion and less matter not trapped yet. In about one google years, the average evaporation of black holes may exceed the capture rate (if black holes evaporate). In much less than a google years lots of other stuff will likely happen, so the prediction is likely invalid.

That might be correct if the density was uniform. But it's not.


Even if black holes have captured 99.999999% of the matter in the Universe, the last tiny bit will take almost forever to cature due to 99.999999999% of the cubic light years having no blackholes.

Well, that's the realm we're speculating about: "almost forever".

[DeepSpaceThinker]

I'm no expert but if you gave the universe "forever" to exist and it kept on expanding then eventually the distance between galaxies/blackholes/anything else would be so great that the graviational pull would be negated.

So I would logically have to agree that you could never consume 100% of the matter in the universe into any number of blackholes.

[invisible]

Even if black holes have captured 99.999999% of the matter in the Universe, the last tiny bit will take almost forever to cature due to 99.999999999% of the cubic light years having no blackholes. Neil

Doesn't matter degrade over trillions of years? Whatever escapes being sucked into a singularity will fade away. The only exception I can think of is new matter. I heard that particles spontaneously appear at a sub-atomic level. Come to think of it, isn't space composed of tiny wormholes. Whats the difference betwwen a wormhole and a black hole? Is it purely a matter of scale?

We don't know that 3% of the matter in the Universe is presently in blackholes. In truth we can't see the universe. Only the past universe to a certain distance. Alpha Centaurii could have gone nova 4 years ago. So the universe could be 99% blackholes.

[grant hutchison]

Doesn't matter degrade over trillions of years?Supersymmetry suggests that protons might decay, producing a positron and a neutral pion, which would then decay to a couple of gamma photons. So matter would still exist, in the form of electrons and positrons. There are experimental constraints on the proton half-life, putting it greater than 1031 years.


I heard that particles spontaneously appear at a sub-atomic level.Perhaps you're thinking of virtual pairs, arising from vacuum fluctuations: they disappear again. Or maybe you're thinking of the Steady State theory, which doesn't get much credence these days.


Come to think of it, isn't space composed of tiny wormholes. Whats the difference betwwen a wormhole and a black hole? Is it purely a matter of scale?Again, vacuum fluctuations. They come and go.


We don't know that 3% of the matter in the Universe is presently in blackholes. In truth we can't see the universe. Only the past universe to a certain distance. Alpha Centaurii could have gone nova 4 years ago. So the universe could be 99% blackholes.That would require a bit of a coordinated rush of activity, centred on our location.

Grant Hutchison

[noncryptic]

> If nothing crossed any event horizon(ie no event horizon forms), and all you had was infalling matter, then you could raise a tide.

To quote the Spartans: "If."

Is it not true that according to GR matter can not be seen to pass the event horizon, as observed from a location outside the event horizon? Then as far as all the rest of the universe (outside any event horizon) is concerned, black holes do consist of a shell of energy located at the event horizon of those black holes.
According to GR it looks different when observed from the FoR of in-falling matter, but according to GR both observations are equally valid. Neither is less "real" than the other, but the one that matters in any FoR is the one that that is observed in that FoR. In other words: matter and energy outside an event horizon is affected in ways consistent with observations in the FoR outside an event horizon, which is that nothing passes the event horizon.

[grant hutchison]

Is it not true that according to GR matter can not be seen to pass the event horizon, as observed from a location outside the event horizon?When matter gets close enough to the horizon, its own mass induces the horizon to expands to encompass it. In other words, the small gravitational potential of the infalling mass, added to the gravitational potential just outside the previous event horizon, creates a new, larger zone from which photons can't escape: a new event horizon which contains both the original black hole and the infalling mass. At the extreme, we can see this happen in simulations of black hole mergers, in which the two event horizons reach out towards each other, forming a transient, peanut-shaped horizon which then "rings down" by the emission of gravitational waves to form a single, final black hole with a larger event horizon. All of that process is observable by a distant observer, in the form of gravitational waves.

Grant Hutchison

[Jeff Root]

Say you have a large non-rotating black hole and a smaller but very
massive second object, also not rotating, maybe a neutron star, and
they collide exactly head-on. Just before the neutron star reaches the
position of the original event horizon of the black hole, the new event
horizon will be peanut-shaped. What about just after the neutron star
should have passed the original position of the horizon? Will the
horizon still be peanut-shaped? So that, for a while at least, you can
tell from the shape of the horizon the distribution of mass inside the
event horizon? If so, how long does this last?

-- Jeff, in Minneapolis

[grant hutchison]

Say you have a large non-rotating black hole and a smaller but very
massive second object, also not rotating, maybe a neutron star, and
they collide exactly head-on. Just before the neutron star reaches the
position of the original event horizon of the black hole, the new event
horizon will be peanut-shaped. What about just after the neutron star
should have passed the original position of the horizon? Will the
horizon still be peanut-shaped? So that, for a while at least, you can
tell from the shape of the horizon the distribution of mass inside the
event horizon? If so, how long does this last?It depends on the total mass. Frans Pretorius (one of the people who did the first numerical simulations of black hole mergers), gives some characteristic times for black hole mergers in a set of slides here (http://physics.princeton.edu/~fpretori/STSCI_2009.pdf) (195KB pdf).
According to that, the ringdown timescale for a pair of black holes merging to form a final solar-mass black hole with no rotation is about 54 microseconds, and scales directly with the total mass. There's no parameter in there for the relative masses involved, so I'd guess this will also give an OOM estimate for your scenario, too.

Grant Hutchison

[neilzero]

That is complicated by essentially all black holes rotating/ most rapidly with respect to nearly all other bodies, everywhere, or perhaps rotation is absolute instead of relative? Is a few rotations per second lots different than non rotating reguarding mergers? I picture solar mass black holes rotating thousands of times per second. Some neutron stars rotate that fast and they are much larger than solar mass event horizons.
Seems to me that sling shot maneuvers occur due to close approaches, instead of collisions, unless a dense accretion disk decelerates the bodies significantly = one collision of black holes per century for the entire visable Universe? Only super massive black holes have event horizon radius larger than Jupiter, so most black holes are a tiny target.
Is there perhaps one or more black holes per cubic light year in the volume of a typical galaxy? Neil