Black hole mass coupled to expansion -- astrophysical source of dark energy?

[Ken G]

Big Bang => Inflation => temperature goes down as the universe expands => pockets of matter start to form as temperature goes down => some of those pockets of matter form black holes and generate dark energy inside them => dark energy accelerates the expansion further => ...

Yes, that's the idea, so it's kind of like a second inflation, long after the first one and much more gradual. But you do raise the interesting possibility that if we can better understand the current slow "inflation", then perhaps we can also learn something about that first, very rapid, inflation.

 

[artis]

No. The model is that ordinary stuff falling into black holes becomes what we have been calling dark energy inside the hole. Nothing is being radiated from them, and there is no dark energy outside black holes.

This whole discussion is way over my head but that statement in particular seems very strange. If there is no dark energy outside the BH and nothing is being radiated out, why is the universe undergoing an accelerated expansion?

Ok but the emphasis is here on the mechanism by which spacetime expansion is achieved.
So without this expansion aka zero point energy/vacuum energy of space all of matter even if once expanded by the energy density of it would later "crunch" or implode back onto itself due to gravity, this we know, so since all of space has a matter distribution within it we can then calculate the "pull" but we now know for the past decades that this "pull" is counteracted by a universal "stretch" force.As far as I understood so far (and probably wrongly) is that the accelerated expansion was thought to arise from the zero point/vacuum energy that permeates all of space and a specific component of that called "dark energy", the main takeaway being that it fills all of space in a uniform fashion and directly acts upin spacetime itself but doesn't interact with ordinary matter.

Based on what you say @Ibix and of what I understand from this latest paper is that they turn around this idea and say that the dark energy is not in empty space spread out evenly but rather it resides in specific "points" within space namely black holes and particularly very massive ones?

To make a crude analogy, instead of being thought to be this uniform force filling all of space it is now supposed to be this concentrated force within a specific object that then acts upon the rest of space like a peg acts upon a piece of clothing hanging on a string.

If so far this is true, I am still puzzled how can dark energy affect space without ever "going outside" of the black hole... I can understand how the gravity of a black hole can influence surrounding matter and space but that's because it does " go out" and in a easily detectable way.Not to mention how will we ever prove this theory to be better or correct given we still have no clue nor way to detect dark energy directly nor can we go "visit' the inside of a black hole?

 

[phinds]

I am still puzzled how can dark energy affect space without ever "going outside" of the black hole

Exactly what I am puzzled by

 

[.Scott]

If so far this is true, I am still puzzled how can dark energy affect space without ever "going outside" of the black hole... I can understand how the gravity of a black hole can influence surrounding matter and space but that's because it does " go out" and in a easily detectable way.

The conventional black hole has mass, angular momentum, and charge - all of which are at or within the event horizon - and all of which influence surrounding matter.

 

[phinds]

The conventional black hole has mass, angular momentum, and charge - all of which are at or within the event horizon - and all of which influence surrounding matter.

But they do so locally and their effect drops off with distance. It seems that this new theory says that black holes seriously affect space-time at great distances.

EDIT: I am not, by the way, trying to be argumentative, just trying to get at least a concept of what the new theory says and how it makes sense.

 

[artis]

Thinking further on this I recall the not so distant observation by LIGO of two black hole merger which due to their immense gravity created powerful ripples within spacetime that were strong enough to be still detectable here at earth.

If this dark energy that affects spacetime sits within massive black holes shouldn't we be able to detect "ripples in expansion" whenever such black holes merge or otherwise?Actually if dark energy is within BH then shouldn't the expansion of space be somewhat uneven from place to place? Or is this difference too small to tell given space has a rather uniform distribution of black holes.

But looking at the cloth analogy, if dark energy is spread across all of space as was commonly thought then it's like stretching a cloth at all points which creates and even stretch but if dark energy is within BH only then the stretch should be less even much like a cloth would be stretched only by certain points across it.

This is what I can deduce if what @Ibix said about the dark energy "not going out of the BH" is true.

Because gravity diminishes from an object as radius squared so every massive object impacts every other and if they are on very large scale spread evenly across space that creates an even pull, but if a force doesn't affect space anywhere outside of a certain point then that should create a less even stretch compared to the pull of gravity, somewhat the difference between putting a piece of paper on water surface VS putting it on a few nails.
This doesn't make sense to me now, how does one create an even force that seems very homogeneous and uniform when that force is said to interact with space only within a very small limited part of it.

 

[PeterDonis]

the claim is that certain types of black holes by whatever unknown mechanism radiate "dark energy"

No, they don't "radiate" dark energy. Dark energy isn't something that is "radiated". They have dark energy in their interiors.

given every black hole in existence was created out of ordinary matter collapsing that would mean they also "radiate" ordinary gravity.

Ordinary gravity doesn't get "radiated" either. The dark energy objects we are discussing have masses just like ordinary black holes. The phase transition in the collapsing matter that creates dark energy in the deep interior of these objects doesn't change their externally measured masses. The main change is in their internal pressure.

So these special types of BH radiate both gravity and dark energy?

No. See above.

in terms of gravity they add to the total matter made gravity constant within the universe

No. The process of the collapsing matter turning into dark energy in the deep interior of these objects doesn't change the total mass.

in terms of dark energy they add to the total acceleration potential observed within the universe?

I'm not sure what you mean by "acceleration potential". It adds to the amount of dark energy in the universe.

 

[PeterDonis]

gravity diminishes from an object as radius squared

No. We are not talking about Newtonian gravity, we are talking about General Relativity. You can't use Newtonian reasoning in this context.

 

[artis]

No. We are not talking about Newtonian gravity, we are talking about General Relativity. You can't use Newtonian reasoning in this context.

True , I got carried away by thinking about this to the point where I forgot that gravity doesn't radiate outwards like EM but is instead considered a spacetime curvature caused by any massive object from single atoms to large stars.

They have dark energy in their interiors.

But this is what puzzles me, so the BH is otherwise just like a normal BH gravity wise and space curvature wise, but this dark energy that is inside it has to be more concentrated within such a BH than it would be if the dark energy was simply spread out evenly across all of space, would this then not cause an uneven acceleration ratio between places of no black holes VS places of a black hole?

 

[paul leonard]

Please unpack this for those of us that don't specialize in cosmology, astrophysics or mathematical solutions to equations of General Relativity. I what I think I got out of this is that:
1. the mass of black holes grows with time, generally in proportion to distance/spectral redshift.
2. blackholes either:
a. "eat" the "dark energy", or
b. "spit out" the "dark energy", which is now causing expansion of the universe
and I am confused as to which is meant.
3. if matter interacts with "dark matter", do black holes also "feed" on "dark matter"

Thanks.

 

[.Scott]

But this is what puzzles me, so the BH is otherwise just like a normal BH gravity wise and space curvature wise, but this dark energy that is inside it has to be more concentrated within such a BH than it would be if the dark energy was simply spread out evenly across all of space, would this then not cause an uneven acceleration ration between places of no black holes VS places of a black hole?

These are similar to my questions at post #35 in this thread.

Would it be fair to say that the dark energy has an effect on the geometry of the space around the black hole?
If there is a geometric effect, is in more potent local to the pseudo-BH?

 

[artis]

These are similar to my questions at post #35 in this thread.

Would it be fair to say that the dark energy has an effect on the geometry of the space around the black hole?
If there is a geometric effect, is in more potent local to the pseudo-BH?

Well if the said BH has that dark energy inside it then that BH has to impact the expansion of space through that dark matter, but given it has to be more concentrated within the BH then also the expansion of space around such a BH has to be larger than far away.

Not sure whether we should call it a "pseudo" BH because it is otherwise to an outside observer just a regular BH, it has all the same properties outside including gravity, horizon etc.

But I think from what i understand so far that the expansion within the space where the BH is located has to be as you say "more potent" aka larger than in an empty space. Because if what @PeterDonis said is correct then by whatever unknown mystery process the matter that fell in is now the source for the dark energy that then couples to the expansion of space. Now matter in a BH is much more dense and concentrated than outside so therefore I would think the dark energy resulting from it also has to be more concentrated there then in empty space.
But from what I understand this isn't what we observe , as space expands uniformly, so how can a concentrated source of dark energy result in the effect of that energy being very homogeneous across all of space irrespective of the density of the energy source.

I will have to read more on this to get a grip on the issue.

 

[artis]

Please unpack this for those of us that don't specialize in cosmology, astrophysics or mathematical solutions to equations of General Relativity. I what I think I got out of this is that:
1. the mass of black holes grows with time, generally in proportion to distance/spectral redshift.
2. blackholes either:
a. "eat" the "dark energy", or
b. "spit out" the "dark energy", which is now causing expansion of the universe
and I am confused as to which is meant.
3. if matter interacts with "dark matter", do black holes also "feed" on "dark matter"

Thanks.

Keep in mind I'm learning this myself but here goes.

1) Mass of black holes generally speaking grows with accreted matter not time, if there is no matter around it then it doesn't have a source to grow from, much like if I take away your food you have no source of energy. This new theory brings some changes to this but others will have to answer to that

2)According to the new theory and even within theories we know so far black holes don't "eat" dark energy nor they spit it out. Black holes accrete matter due to gravitational attraction , in some black holes according to the new theory this matter once inside , by whatever currently unknown mechanism becomes a source for dark energy. dark energy then further doesn't interact with ordinary matter but it does couple to space itself causing it's expansion thereby counteracting gravity which causes attraction.

3) you mean dark matter or energy? I suppose energy, dark energy doesn't interact with ordinary matter that's the problem that's why all these prominent scientists as well as we here are doing a guessing game.
The truth here is simple, dark energy is called dark because we have no real clue as to what it really is we merely observe it's effects on space, we also don't have a direct way to observe empty space, therefore we observe the matter within space like galaxies where we note that they fly away from us at ever faster rates, given galaxies are located within space we therefore say that something is causing space to expand in an accelerated manner.
This we say/speculate is dark energy, now theres a new theory on where that energy might come from , does this somewhat answer your questions?

 

[.Scott]

Not sure whether we should call it a "pseudo" BH because it is otherwise to an outside observer just a regular BH, it has all the same properties outside including gravity, horizon etc.

As I understand it, a true event horizon never forms.

Now matter in a BH is much more dense and concentrated than outside so therefore I would think the dark energy resulting from it also has to be more concentrated there then in empty space.

I'm not sure I would say that "matter" is more dense. Certainly the average mass density is, but except possibly at the singularity, is there actually any dense or compressed matter?

But from what I understand this isn't what we observe , as space expands uniformly, so how can a concentrated source of dark energy result in the effect of that energy being very homogeneous across all of space irrespective of the density of the energy source.

On the face of it, it would seem to be impossible for it to be always uniform. If so and if I could control the production of many "local" stellar BHs, could I send signals to my penpal living outside the observable universe - say 100B LYs away?

 

[Ibix]

I think (not sure) the black holes contribute a term to the Friedmann equations that is like a cosmological constant.

That's what I'm understanding, yes.

 

[Ibix]

Let me see if I have a workable picture.
Would it be fair to say that the dark energy has an effect on the geometry of the space around it?

Let's see if I be more specific in my question: If there was only one supercluster of galaxies in the universe that had stellar-mass black holes, would the result be that the accelerating expansion would be "centered" or "concentrated" about that supercluster?

Don't know. You need a reasonably uniform distribution of stress-energy (however exotic) for an FLRW solution to be a reasonable model, and I don't know how a lump of something exotic in a universe that's otherwise full of regular matter looks like.

 

[PeterDonis]

so the BH is otherwise just like a normal BH gravity wise and space curvature wise

Not really. A "normal" BH is vacuum inside. These objects aren't.

this dark energy that is inside it has to be more concentrated within such a BH than it would be if the dark energy was simply spread out evenly across all of space

Yes. But that's equally true of all the ordinary matter in the universe.

would this then not cause an uneven acceleration ratio between places of no black holes VS places of a black hole?

No more than the fact that the ordinary matter in the universe is clumped causes uneven deceleration. Our cosmological models are averages over large distance scales. I already pointed this out back in post #14.

 

[PeterDonis]

You need a reasonably uniform distribution of stress-energy (however exotic) for an FLRW solution to be a reasonable model

Only on large distance scales. Which is all our cosmological models using FRW spacetime claim to represent. Having dark energy clumped on smaller scales but averaged to a uniform density on large scales doesn't break the models any more than having ordinary matter that way does.

 

[PeterDonis]

If there was only one supercluster of galaxies in the universe that had stellar-mass black holes

Meaning, there are other superclusters, but only this one has these dark energy containing objects?

would the result be that the accelerating expansion would be "centered" or "concentrated" about that supercluster?

The result would be that we could not use an ordinary FRW model for this spacetime, because one significant component of the stress-energy, the dark energy component, does not have a reasonably uniform average distribution on large distance scales. We would have to find a different kind of model, for example a de Sitter patch occupying a spherical region, surrounded by a matter dominated FRW patch. I don't think anyone has investigated such a model, but that's the sort of thing that would be required given the scenario you describe (but we have no reason to think that the scenario you describe holds in our actual universe).

 

[PeterDonis]

I am still puzzled how can dark energy affect space without ever "going outside" of the black hole

You could ask the same question of ordinary matter. The ordinary matter in our universe is not actually a uniform fluid filling all of space. It's clumped. So how can it affect expansion (with deceleration in this case, not acceleration--but that's what our universe was doing until a few billion years ago, since until then the ordinary matter dominated) in the areas it's not occupying?

 

[Ibix]

Only on large distance scales.

Yes, but .Scott seemed to me to be talking about a single region containing dark energy surrounded by a universe otherwise devoid of it. As he said: "only one supercluster of galaxies in the universe that had stellar-mass black holes".

That seems like a job for an "excise a hole from FLRW and insert a different FLRW patch". Except that the paper said doing that was what went wrong with black holes patched in, and I don't know if you can match the boundaries anyway.

 

[artis]

You could ask the same question of ordinary matter. The ordinary matter in our universe is not actually a uniform fluid filling all of space. It's clumped. So how can it affect expansion (with deceleration in this case, not acceleration--but that's what our universe was doing until a few billion years ago, since until then the ordinary matter dominated) in the areas it's not occupying?

I get it , all these models deal with very large scales where matter/dark energy can be considered as uniformly spread because the sources of them are uniformly spread within such large scales.
Get down to lower scales like our solar system and the spread becomes much more uneven. Much like approaching a BH the curvature gets steeper and steeper the closer you get.
Because close to a large body of mass you are almost entirely influenced by just that body while being far away all such bodies ad their influence equal out and balance out to a certain average parameter.

 

[artis]

So getting back to the local effects instead of the averaged out universal ones, I read this article
https://www.universetoday.com/160139/are-black-holes-the-source-of-dark-energy/

These dormant galaxies have little material left for their SMBHs to accrete, meaning that further growth cannot be explained by the two mechanisms mentioned above. The team then compared observations of these elliptical galaxies – which still appear young – to local galaxies dated to ca. 6.6 billion years ago, which have since become dormant. These observations revealed that the SMBHs were 7 to 20 times larger than they were nine billion years ago, much greater than what is predicted by accretion or mergers.

So I get it from what their saying that "we have a bunch of big black holes that have gotten bigger despite not being able to accrete matter by known ways" therefore they had to expand by some other method.

So if they do have dark energy concentrated within them then the black hole could inflate itself simply because the space that it occupies expands more than empty space and it does so because the space that the black hole occupies has more dark energy than empty space.But this seems to me like a positive feedback cycle - you have a region of space with concentrated dark energy which expands more because of it, but then again that region is also a SMBH and as a supermassive black hole it accretes matter that comes close to it, so the BH accretes matter - it gains mass and the curvature of space around it increases this then goes on until equilibrium is established and no more mass surrounds it that it could swallow, but because that mass already inside turns to dark energy, the BH can grow more than it could because the space that it occupies expands so now the BH gets' larger and can accrete new mass that it couldn't before, this again creates more curvature of space around it + more dark energy within it, space expands more expanding the black hole.
Isn't this a positive feedback mechanism and where does it stop?
Shouldn't such BH's swallow up their entire galaxies with nothing left behind?

 

[PeterDonis]

.Scott seemed to me to be talking about a single region containing dark energy surrounded by a universe otherwise devoid of it.

Yes. Which means the stress-energy content is not uniform on large distance scales--it has one region with dark energy and the rest without.

That seems like a job for an "excise a hole from FLRW and insert a different FLRW patch".

Isn't that what I said? (de Sitter is one kind of FLRW model)

 

[PeterDonis]

I get it from what their saying that "we have a bunch of big black holes that have gotten bigger despite not being able to accrete matter by known ways"

This assumes that their model for predicting accretion by known ways is correct. But there is a lot of uncertainty in our understanding of how those processes work.

if they do have dark energy concentrated within them then the black hole could inflate itself

That's basically the model being proposed, yes.

Shouldn't such BH's swallow up their entire galaxies with nothing left behind?

Not necessarily. Galaxies are still many orders of magnitude larger than even the largest SMBHs.

 

[.Scott]

Here's another article discussion this topic: Physics World

 

[PeterDonis]

being far away all such bodies ad their influence equal out and balance out to a certain average parameter.

That's the basic idea, yes.

One possible wrinkle that I can see, though, is that for ordinary matter, for which pressure is negligible, the only thing that has to be averaged is the mass density. But for dark energy (and also for radiation), pressure is not negligible, so if the actual distribution is not uniform pressure would have to be averaged as well as mass density.

I don't know that anyone has investigated whether it is in fact valid to average pressure that way--i.e., whether a "fluid" made of clumps of something with non-negligible pressure, when averaged over a large scale, has the same equation of state, with the same pressure as a function of density, as the individual clumps do. For radiation, this isn't an issue, because when the universe was radiation dominated, the radiation was uniformly distributed to very high precision, not clumped (we know that because the CMB is uniformly distributed to very high precision, about 1 part in 100,000), so nobody ever had to ask whether "clumps" of radiation would average.

Up to now, it was assumed that dark energy was also uniform, not clumped, so nobody ever had to ask whether "clumps" of dark energy would average. But with this proposed model, that question now becomes relevant and would need to be answered. The proposed model doesn't answer it as far as I can see; it just assumes that the averaging works. It's possible that there is a simple answer somewhere, but I have not seen one.

 

[.Scott]

If I understand these articles, the mass that a BH gains from this coupling may somehow be constrained by the conservation of matter and energy, but not necessarily.

Perhaps if we stand aside, measure what comes out, and wait for the BH to evaporate, we might discover that the mass of the evaporation is the same as the mass accreted into the BH - while the mass from coupling is lost again.

Or perhaps it is constrained by mass conservation - and its increase in mass by coupling somehow balances out with the effect it has on Cosmological Constant?

 

[.Scott]

As I understand it, dark energy "pressure" has the effect of accelerating motion in the radial direction. So any dark energy carried by Sgr A* would have little effect on most orbiting galactic star (including our own sun) but a direct effect on anything fleeing or approaching Sgr A* - such as the stars that are in very close elliptical orbits around Sgr A*. Shouldn't that be observable?

 

[PeterDonis]

As I understand it, dark energy "pressure" has the effect of accelerating motion in the radial direction.

More precisely, it has the effect of causing a small ball of test particles, initially at rest relative to each other, to expand (whereas ordinary matter would cause it to contract). But this assumes that the test particles are immersed in the "fluid" of dark energy (or ordinary matter). It says nothing about any vacuum region outside the fluid.

In cosmological models, the "fluid" that appears in the models is, as already noted, an average of whatever stress-energy is present, taken over large distance scales.

any dark energy carried by Sgr A* would have little effect on most orbiting galactic star (including our own sun) but a direct effect on anything fleeing or approaching Sgr A*

No, it wouldn't. See above.

 

[Ken G]

No. The process of the collapsing matter turning into dark energy in the deep interior of these objects doesn't change the total mass.

Your posts have been extremely helpful, so thank you, but I'm not sure what you mean by this one. An essential piece of this new model is that the observable mass of black holes (which is essentially their relatively normal and Newton-like effects on nearby gas) does increase with time, without any accretion,, and that this mimics a cosmological constant if it increases with time in proportion to the increase in volume of the universe (essentially because any energy that increases in proportion to the volume of the universe acts like a cosmological constant). The observational evidence they cite for the model is that the black hole masses appear to be increasing with time, even without accretion, at the same rate as the expansion of volume of the universe. So if we are picturing this by saying that dark energy is being created inside the black hole, then this creation nothing to do with accretion, it is coupled directly to the expansion, and it comes alongside black-hole mass increases that also have nothing to do with accretion.

 

[.Scott]

An essential piece of this new model is that the observable mass of black holes (which is essentially their relatively normal and Newton-like effects on nearby gas) does increase with time, without any accretion...

I believe it's a two-step process.
1) Creation of Dark Energy during the collapse (and subsequent accretions);
2) Dark Energy coupling inflates mass.

 

[PeterDonis]

I'm not sure what you mean by this one.

I mean that, simply due to local conservation of stress-energy, a phase transition inside the collapsing matter during the collapse cannot change the externally measured mass.

An essential piece of this new model is that the observable mass of black holes (which is essentially their relatively normal and Newton-like effects on nearby gas) does increase with time, without any accretion

Yes, but that's not due to the collapse process, it's due to a claimed coupling with the overall expansion of the universe. That coupling only comes into play on time scales much longer than the collapse time scale.

if we are picturing this by saying that dark energy is being created inside the black hole, then this creation nothing to do with accretion

That's correct, but if dark energy is not created inside the object, then there's nothing for the claimed coupling described above to work on. Ordinary collapsing matter does not contain any dark energy. So at some point during the collapse process, the ordinary collapsing matter has to somehow be converted to dark energy (i.e., some kind of phase transition has to occur) in order for the claimed coupling to have the effects it is claimed to have.

 

[.Scott]

In the paper, the coupling exponent "k" is roughly 3. But there is a scaling term $a_i$ that is never estimated.
I don't understand why.

 

[.Scott]

Yes, but that's not due to the collapse process, it's due to a claimed coupling with the overall expansion of the universe.

I would describe it as an "apparent coupling". Since they have excluded "no coupling" to a confidence of 99.98%, either there's something very misleading in the data collection or we're very lucky (or unlucky) in spotting a well-formed pattern from random data.