Origin of suspected black hole in Omega Centauri

[oldman]

Omega Centauri is suspected of being centred on a black hole and of perhaps being the remnant of a small galaxy rather than just a globular cluster. Could someone tell me, in either case, what the the accepted view is of how the black hole got there? Was it created as the star cluster formed? By gravitational collapse? Or did it seed cluster creation somehow? Why should black holes be found at the centres of galaxies? Did dark matter play a role in decorating galaxies and possibly star clusters with central black holes?

 

[oldman]

I've just seen this:

According to Dr Robert Massy, of the Royal Astronomical Society, the results (of researchers who confirm the existence of a black hole at the Milky Way centre) suggest that galaxies form around giant black holes in the way that a pearl forms around grit... Dr Massy said: "Although we think of black holes as somehow threatening, in the sense that if you get too close to one you are in trouble, they may have had a role in helping galaxies to form - not just our own, but all galaxies"

Any clarifications of how and why this happens?

 

[stevebd1]

While not strictly mathematical, it does give some insight into the connection between galaxies and the supermassive black holes at their centres-



regards
Steve

 

[Arch2008]

Here’s a link to a story in Astronomy magazine about the earliest galaxies ever imaged by Hubble.
http://www.astronomy.com/asy/default.aspx?c=a&id=2070

For about three thousand centuries after the Big Bang, dark matter started collapsing into spongy clouds. As the universe cooled, protons and electrons eventually combined to form hydrogen (and some helium and lithium). These elements collapsed by the gravity of the already formed DM clouds and became stars. As with stellar nurseries today, some huge stars formed and after a few million years these stars went supernova. Some of the supernova remnants were black holes. Over the passage of time, the clusters of stars continued to collapse and through mergers ever more massive black holes formed. The gravity of the largest BH’s formed ever larger clusters. So why didn’t all the matter just fall into the BH? When a BH reaches a certain mass, more matter is “falling in” than can pass into the BH and the “run off” forms two opposing jets of energy thousands of light years long. When these objects were first observed they were titled Quasi-Stellar objects, or Quasars. Now the objects are called Active Galactic Nuclei or AGN. One of the side effects of this “quasaring” is that a shock wave forms and drives matter away from the BH. So the BH “switches off” and a galaxy of stars forms around it attracted by its gravity and held in place by the DM cloud. This is the most plausible theory.

 

[oldman]

Here’s a link ...This is the most plausible theory.

Thanks for both the link and the clear summary of how people think galaxies come to be as they are. The seeming ubiquity of black holes in galaxies --- and perhaps even in smaller stellar structures --- is fascinating. Have you any links to more technical histories, say on the Arxiv? If so, I'd appreciate them.

stevebd1: thanks for this link, but my link is too slow to watch anything. If you have any text-type links I'd also like to follow them.

 

[stevebd1]

Here's the transcript (credit to the BBC)-

http://www.bbc.co.uk/science/horizon/2000/massivebholes_transcript.shtml

While Horizon is above average when compared to the average pop science programme, it still has it's fair share of filler so you might want to be selective when reading the text but there is useful information in there.

regards
Steve

 

[oldman]

Here's the transcript ...there is useful information in there.

Trust the Beeb to come up with an excellent program. Thanks for this link, Steve, it's really useful and informative -- and quick to download on GPRS.

I notice that the program was broadcast some eight years ago, before really convincing evidence for dark non-baryonic matter via gravitational lensing in, say, the Bullet cluster was available, and before the WMAP results showed that most of the matter in the universe is indeed dark stuff. Unsurprisingly, there was then no pressing need to consider how dark matter collapses.

Do you know whether central black holes are thought (initially) to be made of non-baryonic stuff, or not, and if not -- why not? It seems to me than unlike the collapse of ordinary matter that interacts through all known channels (electroweak, strong and gravity), there is not much that can 'terminate' the infall of dark matter, except the formation of an event horizon. Has this sort of argument been considered?

I notice also that Arch2008 above refers to dark matter 'collapsing into spongy clouds', so the collapse has indeed been modeled, and is an important part of structure formation.

 

[Arch2008]

A lot of the hard data pieces to this puzzle have only been collected in the last couple of years or less.

Here is a description of how primordial clouds of DM and normal matter collapse:
http://arxiv.org/PS_cache/astro-ph/pdf/9808/9808072v1.pdf

How globular clusters and Dwarf Galaxies merge:
http://www.astronomy.com/asy/default.aspx?c=a&id=7515
http://arxiv.org/PS_cache/arxiv/pdf/0810/0810.2800v1.pdf

Early massive Black Holes in merging galaxies and early galaxy evolution:
http://www.astronomy.com/asy/default.aspx?c=a&id=7529
http://arxiv.org/PS_cache/arxiv/pdf/0810/0810.2795v2.pdf

Space Telescope Abell 901/902 Galaxy Evolution Survey (STAGES)
http://www.spacetelescope.org/news/pdf/heic0802.pdf

STAGES in detail:
http://arxiv.org/PS_cache/arxiv/pdf/0811/0811.3890v1.pdf

http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.3908v1.pdf

http://arxiv.org/PS_cache/arxiv/pdf/0801/0801.1156v1.pdf

 

[oldman]

A lot of the hard data pieces to this puzzle have only been collected in the last couple of years or less...

Now I have an up-to-date set of references I can spend some time digesting. Thanks very much for posting them --- they're just the sort of thing I was looking for.

Perhaps you'd also care to comment on the possible constitution of galaxy-centre black holes? Do they have to form out of early-universe massive and short-lived baryonic-matter stars, or could they also form directly from collapsing clouds of dark matter? I notice that in the Oliveira et al. 1998 paper where the spherical collapse of both dark and baryonic matter were modeled hydrodynamically it was concluded that:

In the collapse of the DM the cooling-heating mechanisms and the photon drag, which are very important for the collapse of the baryonic matter, cannot directly alter the collapse of this component and thus the non-baryonic matter is rapidly concentrated in the innermost region of the clouds

which bears on the question I asked stevebd1 in my previous post.

 

[stevebd1]

Do you know whether central black holes are thought (initially) to be made of non-baryonic stuff, or not, and if not -- why not? It seems to me than unlike the collapse of ordinary matter that interacts through all known channels (electroweak, strong and gravity), there is not much that can 'terminate' the infall of dark matter, except the formation of an event horizon. Has this sort of argument been considered?

One popular candidate for dark matter is the neutralino which, due to being supersymmetric, is it's own anti-particle meaning if it came into too close contact with itself, it would annihilate, producing high-energy gamma rays (this is one process currently being used to detect dark matter). It's believed there is a concentration of neutralinos at the galactic (and solar) centre. While I think it's accepted that dark matter contributes to a black holes mass (as do photons and CMB), I think dark matter on its own would annihilate before collapsing into a black hole.

'An increased density of neutralinos may exist in the vicinity of the Galactic-centre or the Sun. This could have arisen in the initial formation of these objects. Also, neutalinos entering the solar system (or the Galaxy) may lose energy via elastic scattering with ordinary matter and become gravitationally trapped. Because of the capture and repeated scatterings, there would be a near-solar (or Galactic-centre) enhancement in the neutralino density. Such a local neutralino build-up may provide a detectable flux of annihilation products.'
Source- "scipp.ucsc.edu/milagro/papers/PhysRevD_70_083516.pdf"[/URL] Page 2

 

[oldman]

Yes, as you say, if dark matter does indeed turn out to be neutralinos with the expected supersymmetric properties, neutralino-neutralino annihilation could indeed rule out black holes forming from the collapse of dark matter.

But the density of a BH is inversely proportional to the square of its mass. So, if collapsing dark-matter clouds were massive enough, annihilation might be avoided by infalling neutralinos, if that's what dark matter is. The bigger the BH, the easier it forms.

On a lighter note, though, the way you put it:

...the neutralino which ... is it's own anti-particle meaning if it came into too close contact with itself, it would annihilate

is a bit reminiscent of the galoolie bird, which flies in ever decreasing circles until it disappears into its own fundament. Strange things, neutralinos and galoolie birds!

 

[Arch2008]

http://en.wikipedia.org/wiki/No_hair_theorem

Supposedly, the Black Hole's at the center of galaxies are the end result of countless mergers. Dark Matter, like anything else, could become a resident of the singularity. However, as John Wheeler posed, only mass, charge and angular momentum can be discerned from any BH. The information of the contents of the BH will only return as Hawking Radiation. However, it is possible that anything entering a BH becomes “frozen in time”, and thus a record remains plastered on the event horizon of everything that ever met this fate. So at least a theoretical possibility exists to decipher how much DM content is in this enigma.

 

[stevebd1]

But the density of a BH is inversely proportional to the square of its mass. So, if collapsing dark-matter clouds were massive enough, annihilation might be avoided by infalling neutralinos, if that's what dark matter is. The bigger the BH, the easier it forms.

You can make a stab at how big a cloud of dark matter would have to be in order to collapse into a black hole, based on DM being neutralinos and the DM density* of our galaxy being the critical density before neutralinos begin to annihilate each other (~3.739e-23 kg/m^3, which based on the neutralino being about 1 TeV, works out at about 21 neutralinos per m^3, which still seems quite high, though the neutralino might be anything up to 10 TeV) using the equation put together by George Jones in https://www.physicsforums.com/showthread.php?p=1406792#post1406792"-

M = \frac{c^3}{4}\sqrt{\frac{3}{2\pi G^3}}\sqrt{\frac{1}{\rho}}

where ρ is density

Based on the parameters above, the answer comes out at about 1.396e+51 kg. Based on the supposed density of dark matter in our galaxy, this provides a volume of 3.734e+73 m^3 which is equivalent to a sphere with a radius of 219 million Lys.

*Based on a DM mass of 1.8e+12 M_☉ within a sphere of r=3e+5 Lys.

 

[oldman]

Thanks for your estimate of how big a ball of neutralinos would have to be to collapse to a BH without disappearing in a blast of gamma rays.

...a sphere with a radius of 219 million Lys.

Two orders of magnitude too big to account for supermassive BH's in galax centres!

Must one then conclude that the universe is littered with supermassive BH's that are created by an evolutionary process of gravitational collapse, accretion and mergers --- a process where only 15% of the universe's gravitating matter plays the central role? Remember that the collapse of baryonic matter is impeded and delayed by an intermediate chrysalitic stage of stellar existence, while the gravitational collapse of the remaining 85% dark mass fraction is free-fall, not so impeded.

It seems very odd to me that the fate of these two mass components should be so disparate --- baryonic matter forming BH's, dark matter forming diffuse haloes and spongy clouds.

Perhaps, as you seem to imply, Steve, the strange self-annihilating nature of neutralino dark matter is the key to this puzzle.

 

[George Jones]

Do you know whether central black holes are thought (initially) to be made of non-baryonic stuff, or not, and if not -- why not? It seems to me than unlike the collapse of ordinary matter that interacts through all known channels (electroweak, strong and gravity), there is not much that can 'terminate' the infall of dark matter, except the formation of an event horizon. Has this sort of argument been considered?

Just thinking "out loud". Is it possible to turn this argument around?

If collapse of a clump of dark matter is asymmetric enough, parts of the clump will miss other parts, i.e., they will stream by each other. Couldn't "friction" (not sure if this is the right term) play a role in focusing an slightly asymmetrical collapse of baryonic matter, so that a black hole does form? Could "friction" play the same role in the accretion of stuff onto already formed black holes? Does this make any sense??

This appears to be active area of research. Here,

http://arxiv.org/abs/0802.2041,

is a recent paper, but I don't how accepted are its results.

 

[oldman]

Could "friction" play the same role in the accretion of stuff onto already formed black holes? Does this make any sense??

The link you gave is very helpful. Thanks. And your comment about "friction" is, I think, germane to the peculiarities of dark matter collapse that have puzzled me. But I can't tell you how much sense it makes! I don't even know whether the following comments are relevant (or correct).

Cosmological dark matter is thought to be stuff that interacts with itself and other matter only via gravity. This is why, I think, in the link you gave, Peirani and Pacheko say that "dark matter particles constitute a collisionless fluid". They then add: "and, consequently, the accretion process should be less efficient than that expected for a dissipative fluid". Finally they conclude, in agreement with this statement that "dark matter contributes to no more than ∼ 10% of the total accreted matter" (of an SMBH).

The peculiarity that still puzzles me is why they assume that: "the accretion process (for dark matter) should be less efficient than that expected for a dissipative fluid (baryonic matter)" . It seems that "friction" (perhaps of the kind you were thinking of?), which I would have expected to slow processes down, instead seems to allow them to proceed faster.

I can only speculate that this must have to do with the slowness of virialising a collapsing structure in the absence of dissipative mechanisms like radiation emission. This may be why dark matter collapse, which P & P say is like adiabatic infall but with a modified adiabatic constant, is slow by comparison with baryonic matter collapse, but I don't really understand exactly why this should be so. I had fixed in my mind that dark matter would be like free-fall collapse --- not impeded by the formation of virialised structures like hot gas clouds and ultimately stars -- and therefore faster than baryonic infall. I guess the opposite is true -- the infall process is a lot more complicated than I thought.

 

[Arch2008]

Oldman, you may find this of interest.
http://www.astronomy.com/asy/default.aspx?c=a&id=6368

It still needs a lot of modeling and of course, that proof thing.:)

 

[oldman]

Oldman, you may find this of interest.
http://www.astronomy.com/asy/default.aspx?c=a&id=6368

It still needs a lot of modeling and of course, that proof thing.:)

Thanks. It's interesting to find that strange structures partly made of dark matter, like large 'fluffy' dark stars and fast-forming BHs, proposed by Paulo Gondolo, are being considered.

Since dark matter is thought to make up about 85% of all matter in the universe --- a major fraction, indeed --- surely one should guess that its gravitational collapse must somehow create a variety of structures other that 'spongy clouds' and 'dark haloes'. These were the only ones I'd seen mentioned until I followed the link you gave.

Other questions that still puzzle me are: What kind of dissipative mechanisms could facilitate collapse in a very nearly uniform collisionless gas of particles that is the dark matter of the early universe? Or: How can the virial theorem permit pure dark matter to collapse at all?

 

[George Jones]

Other questions that still puzzle me are: What kind of dissipative mechanisms could facilitate collapse in a very nearly uniform collisionless gas of particles that is the dark matter of the early universe? Or: How can the virial theorem permit pure dark matter to collapse at all?

I think this is caused by self-gravity and slight fluctuations in density. See the links given in

https://www.physicsforums.com/showthread.php?p=1847031#post1847031.

 

[oldman]

I think this is caused by self-gravity and slight fluctuations in density...

Thanks, George. I've used this link to Wolram's thread 'Sky map and dark energy', and have also read your #10 post there about the details of the growth of overdense regions. I've also been reading a recent paper by http://arxiv.org/abs/0810.2802" about ' Pathways to massive black holes and compact star clusters in pre-galactic dark matter haloes with virial temperatures > 10000K'. which is relevant to the formation of SMBHs.

My remaining difficulty is of a more general nature, though.

It is this: for any structure to form by gravitational collapse and then endure in a collapsed state (rather than to eternally oscillate between its original configuration and its compact confuguration) mass/energy must be dissipated or removed from the structure. Examples: infall and capture in a closed orbit by a star of a object approaching along a hyperbolic path ; return of the Apollo missions to Earth; the birth of a star from a collapsing gas cloud (allowed by radiative dissipation), etc. etc.

It's a conservation of energy thing mandated (in stellar genesis) by the virial theorem.

I have so far been unable to find an description of the mechanism by which mass/energy is similarly removed form collapsing non-baryonic dark matter in order to stabilise an increasingly overdense region. It's probably so obvious a mechanism to workers in the field that they don't bother to mention it, just as people don't bother to mention that the emission of radiation is the crucial mechanism that allows a stable star to form. It's so obvious.

If one imposes suitably periodic boundary conditions on the (possibly infinite) universe to divide it up into imaginably finite pieces this question is accentuated, since across such boundaries one expects the net flux of mass/energy to be zero --- unless the universe is expanding (which it is!).

So perhaps in the end structure formation is only possible in an expanding universe??

 

[oldman]

In my previous post I asked if:

... perhaps in the end structure formation is only possible in an expanding universe??

The arguments I gave are supported by Janus's remark in another recent https://www.physicsforums.com/showthread.php?t=280647":

Dark matter neither sticks together nor can it shed energy by radiating. As it falls toward the center of the Earth, it picks up kinetic energy, and with no interaction or radiation, it has all that kinetic energy when it reaches the center, and this kinetic energy carries it back out of the Earth. There is no way for it to collect there.

and by Marcus's comment in the same thread that:

Dark matter doesn't clump very easily ... (it can) jettison excess kinetic energy (by)
Gravitational (e.g. slingshot) interaction. DM can give away KE to ordinary or to other DM. Then it has less and can clump.

The other DM that took away the extra KE will itself eventually be slowed down by the universe expansion process and may get a second chance to clump...

We know that expansion drains energy from light, from radiation---that is the usual cosmo redshift. So it should not be completely surprising that particles with mass are gradually slowed down by expansion (seen from standpoint of observer at rest relative to cosmic Background.)

.

We certainly live in a phase of the universe that is filled with structures made of matter (lots baryonic and probably more dark). One could take this as proof that expansion is a necessary feature of the universe's evolutionary history. Although such proof may seem redundant (since cosmologists already accept that the redshift is proof of expansion) redshift is in fact only a necessary consequence of expansion in a universe ruled by the Friedmann-Robertson-Walker metric; redshift is not sufficient proof that the universe is expanding. It tells us only that the ratio of metric coefficients in the RW metric changes with time. It is the formation of structures like the ones we observe that confirms that the scale factor is the metric coefficient that runs with time, as usually assumed.

The phase of the universe thought to have preceded the evolution of the structures we now observe is inflation. It is here conservatively assumed that inflation is an extreme version of the very same process that allows structure to evolve, namely expansion. Inflation then resolves various difficulties like the horizon and flatness problems. But these difficulties can also resolved by letting the metric coefficient c (a.k.a. a unit-conversion factor or the speed of light) vary, as in the VSL theories of say, Magueijo and Moffat. In this early phase of the universe's evolution there is no question of structure evolution, because it's too hot, and therefore no confirmation that expansion is involved.

I'm left wondering whether the inflationary scenario is not a phase in which c evolves, rather than structure.

 

[oldman]

In a previous post (#20) I commented that:

:...I have so far been unable to find an description of the mechanism by which mass/energy is similarly removed form collapsing non-baryonic dark matter in order to stabilise an increasingly overdense region. It's probably so obvious a mechanism to workers in the field that they don't bother to mention it, just as people don't bother to mention that the emission of radiation is the crucial mechanism that allows a stable star to form (because) It's so obvious..

I now see in a http://news.bbc.co.uk/2/low/science/nature/7815827.stm" that:

A cosmic chicken-and-egg question has been solved by astronomers, who now say that black holes came before galaxies.

The findings were presented at a major astronomy meeting in California.

Most if not all galaxies, including our own Milky Way, are believed to have massive black holes at their cores.

It was unclear whether black holes came first, helping create galaxies by pulling matter towards them, or whether they arose in already formed galaxies.

"It looks like the black holes came first," said Dr Chris Carilli, from the US National Radio Astronomy Observatory in Socorro, New Mexico, who took part in the study. "The evidence is piling up."

The evidence was unveiled at the 213th American Astronomical Society meeting in Long Beach, California.

Earlier studies of nearby galaxies had revealed an intriguing link between the masses of black holes and the central "bulges" of stars and gas in galaxies...

Does anyone know of a web-accessible description of a simulation of the collapse of a cloud of pure dark matter? I'm beginning to wonder if the mechanism by which such a collapsing cloud could be virialised is perhaps less obvious as I thought, in which case pre-galactic black holes might indeed form from collapsing dark matter?

 

[Suede]

Omega Centauri is suspected of being centred on a black hole and of perhaps being the remnant of a small galaxy rather than just a globular cluster. Could someone tell me, in either case, what the the accepted view is of how the black hole got there? Was it created as the star cluster formed? By gravitational collapse? Or did it seed cluster creation somehow? Why should black holes be found at the centres of galaxies? Did dark matter play a role in decorating galaxies and possibly star clusters with central black holes?

Good question, Einstein says black holes don't exist.

I for one, believe him.

On a Stationary System with Spherical Symmetry Consisting of Many Gravitating Masses.
A. Einstein, Annals of Mathematics Vol 40. No. 4 Oct 1939
http://www.jstor.org/pss/1968902


So does Schwarzschild

On the Gravitational Field of a Mass Point According to Einstein’s Theory
K. Schwarzschild, Sitzungsber.Preuss.Akad.Wiss.Berlin (Math.Phys.) 1916 (1916) 189-196
http://www.sjcrothers.plasmaresources.com/schwarzschild.pdf

 

[oldman]

... Einstein says black holes don't exist. I for one, believe him... So does Schwarzschild

It's not a question of belief, Suede --- it's a question of evidence. In the case of black holes (which are too black to be seen) the evidence is circumstantial. Lots of it has been found since Einstein and Schwarzschild's days. Thanks for your comment, nevertheless.

 

[Suede]

It's not a question of belief, Suede --- it's a question of evidence. In the case of black holes (which are too black to be seen) the evidence is circumstantial. Lots of it has been found since Einstein and Schwarzschild's days. Thanks for your comment, nevertheless.

Surely.

I suppose we all have our own thresholds of belief.

Mine requires falsifiable experimentation and testable physics before I buy into the theory that space is warped into a black hole, which btw, are also supposedly capable of shooting matter out in jets light years across. How exactly an infinitely dense object can manage to shoot jets of matter out light years across is beyond me. Of course if I can't see it, I'm just too dumb to see the emperors new clothes.

Ever stop and think about that one for a minute?

 

[stevebd1]

How exactly an infinitely dense object can manage to shoot jets of matter out light years across is beyond me. Of course if I can't see it, I'm just too dumb to see the emperors new clothes.

I think you may have made a bit of a misconception there. You basically have a lot of matter within the accretion disk which is falling onto/into the black hole which relatively speaking has a small surface area, not all of it gets in and the ultra-relativistic matter 'backs up', some is ejected at the axis of rotation (i.e. the poles) at close to light speed in the form of gamma-ray bursts.

 

[Suede]

I think you may have made a bit of a misconception there. You basically have a lot of matter within the accretion disk which is falling onto/into the black hole which relatively speaking has a small surface area, not all of it gets in and the ultra-relativistic matter 'backs up', some is ejected at the axis of rotation (i.e. the poles) at close to light speed in the form of gamma-ray bursts.

yeah yeah yeah, I know the theory well.

I still think its a total load of nonsense that has no basis in experimental science, is completely counter intuitive, and fails Occam's razor.

My opinion of course.

I'll believe in black holes when we can produce one in a lab.

I could go on and on about why this is so, like how the jets display brightening and diming along their total length, how they are magnetically confined, etc.. etc..

 

[Arch2008]

Oldman, are you looking for something like this?
http://www.ucolick.org/~diemand/earlysubs.pdf

 

[Nereid]

It's not a question of belief, Suede --- it's a question of evidence. In the case of black holes (which are too black to be seen) the evidence is circumstantial. Lots of it has been found since Einstein and Schwarzschild's days. Thanks for your comment, nevertheless.

While BH's will never be 'seen', their immediate environs may well be, and reasonably soon too.

For example (bold added): http://fr.arxiv.org/abs/0809.4677" (a 2008 paper, link is to the arXiv preprint):

Advances in VLBI instrumentation now allow wideband recording that significantly increases the sensitivity of short wavelength VLBI observations. Observations of the super-massive black hole candidate at the center of the Milky Way, SgrA*, with short wavelength VLBI reduces the scattering effects of the intervening interstellar medium, allowing observations with angular resolution comparable to the apparent size of the event horizon of the putative black hole. Observations in April 2007 at a wavelength of 1.3mm on a three station VLBI array have now confirmed structure in SgrA* on scales of just a few Schwarzschild radii. When modeled as a circular Gaussian, the fitted diameter of SgrA* is 37 micro arcsec (+16,-10; 3-sigma), which is smaller than the expected apparent size of the event horizon of the Galactic Center black hole. These observations demonstrate that mm/sub-mm VLBI is poised to open a new window onto the study of black hole physics via high angular resolution observations of the Galactic Center.

 

[Nereid]

Good question, Einstein says black holes don't exist.

I for one, believe him.

On a Stationary System with Spherical Symmetry Consisting of Many Gravitating Masses.
A. Einstein, Annals of Mathematics Vol 40. No. 4 Oct 1939
http://www.jstor.org/pss/1968902


So does Schwarzschild

On the Gravitational Field of a Mass Point According to Einstein’s Theory
K. Schwarzschild, Sitzungsber.Preuss.Akad.Wiss.Berlin (Math.Phys.) 1916 (1916) 189-196
http://www.sjcrothers.plasmaresources.com/schwarzschild.pdf

There are a number of existing threads in https://www.physicsforums.com/forumdisplay.php?f=70" that you might be interested in reading, and possibly participating in, Suede, that are pertinent to GR, black holes, and misunderstandings of this topic.

GR is far better understood today than it was in 1916.

 

[Nereid]

[...]

Does anyone know of a web-accessible description of a simulation of the collapse of a cloud of pure dark matter? I'm beginning to wonder if the mechanism by which such a collapsing cloud could be virialised is perhaps less obvious as I thought, in which case pre-galactic black holes might indeed form from collapsing dark matter?

Are you familiar with the landmark* NFW (Navarro, Frenk, and White) paper?

http://adsabs.harvard.edu/abs/1996ApJ...462..563N":

We use N-body simulations to investigate the structure of dark halos in the standard cold dark matter cosmogony. Halos are excised from simulations of cosmologically representative regions and are resimulated individually at high resolution. We study objects with masses ranging from those of dwarf galaxy halos to those of rich galaxy clusters. The spherically averaged density profiles of all our halos can be fitted over two decades in radius by scaling a simple "universal" profile. The characteristic over- density of a halo, or equivalently its concentration, correlates strongly with halo mass in a way that reflects the mass dependence of the epoch of halo formation. Halo profiles are approximately isothermal over a large range in radii but are significantly shallower than r -2 near the center and steeper than r-2 near the virial radius. Matching the observed rotation curves of disk galaxies requires disk mass-to-light ratios to increase systematically with luminosity. Further, it suggests that the halos of bright galaxies depend only weakly on galaxy luminosity and have circular velocities significantly lower than the disk rotation speed. This may explain why luminosity and dynamics are uncorrelated in observed samples of binary galaxies and of satellite/spiral systems. For galaxy clusters, our halo models are consistent both with the presence of giant arcs and with the observed structure of the intracluster medium, and they suggest a simple explanation for the disparate estimates of cluster core radii found by previous authors. Our results also highlight two shortcomings of the CDM model. CDM halos are too concentrated to be consistent with the halo parameters inferred for dwarf irregulars, and the predicted abundance of galaxy halos is larger than the observed abundance of galaxies. The first problem may imply that the core structure of dwarf galaxies was altered by the galaxy formation process, and the second problem may imply that galaxies failed to form (or remain undetected) in many dark halos.

Is this what you're looking for? If not, then perhaps one of the >1000 papers which cite it may be?

* ADS says it's been cited almost 1800 times!

 

[oldman]

Oldman, are you looking for something like this?
http://www.ucolick.org/~diemand/earlysubs.pdf

Yes indeed. Thanks very much for this link, Arch. It reveals that the suggestions I've made are far too oversimplified. I'd suspected that the elements of the physical processes involved in dark matter collapse (like how virialisation occurs) are not easy to disentangle from the complexities of N-body simulations using established codes, like the PDKGRAV code mentioned in this paper. It confirms that I'm in way over my head, and I must refrain from trying to project simple physics onto complex situations.

I guess you choose your input cleverly and then let the computer rip and see what emerges. Must be a bit like simulating say cirrus clouds using Navier-Stokes codes. Effective, perhaps, but not very illuminating for weather forecasters.

 

[oldman]

Are you familiar with the landmark NFW (Navarro, Frenk, and White) paper?

No, I wasn't. Thanks for pointing me at this seminal paper and so helping to modernise my outlook. Coincidentally, I'm familiar with ancient stuff published by (Frank) Nabarro, (Charles) Frank and (Guy) White.

 

[Arch2008]

You’re welcome. The problem with trusting computer models is Garbage In, Garbage Out (GIGO). However, more and more often, simulation has guided research into hopeful directions that then matched observation. I did find one paper where the observation was against galaxies forming from multiple mergers. The researchers had pictures of ancient galaxies that were supposedly too uniform and could only have formed from one huge cloud that collapsed directly into a central black hole with stars.
Their survey consisted of a whopping seven galaxies of which four were “too uniform”!