Do black holes swallow dark matter?

[Naty1]

What do we know about black holes swallowing dark matter? Dark matter exhibits gravitational effects, right [lensing and keeping star orbital speeds about galactic centers rouighly independent of their distance from a galactic center]? So it seems black holes should consume both normal and dark matter.

Are there any theoretical ways to detect the effects of dark matter when it's consumed by black holes?? Anyone seen any discussions or papers?? Thanks?

 

[mathman]

Anything that is consumed by a black hole will add to the mass, charge, and angular momentum. Otherwise there is nothing to to identify it. In particular, dark matter and normal matter cannot be distinguished after being consumed by a black hole.

 

[nicksauce]

Not to mention that there is a minuscule amount of dark matter in the galactic centre, where black holes are "swallowing matter", compared to the amount of baryonic matter.

 

[Chalnoth]

Not to mention that there is a minuscule amount of dark matter in the galactic centre, where black holes are "swallowing matter", compared to the amount of baryonic matter.

Yes. And more important than that, dark matter doesn't experience much of any friction. This means that even if some dark matter gets in the vicinity of a black hole, it tends to just blow on by. It has to actually strike the black hole to go into it (and black holes are pretty darned small for their mass, so hitting one is difficult).

This is contrasted to normal matter which, through friction, enters an accretion disk around the black hole, a disk that slowly collapses into the black hole through loss of energy from friction.

 

[Naty1]

All valid points in the above posts...yet with dark matter making up such a large proportion of all matter seems like it could have an effect...maybe somehow we could observe effects.

Chalnoth...interesting observation

I'm guessing Hawking work on radiation did not reflect any dark matter ingestion...but I wonder if it could be expanded/modified to do so.

 

[Chalnoth]

All valid points in the above posts...yet with dark matter making up such a large proportion of all matter seems like it could have an effect...maybe somehow we could observe effects.

The problem is that the dark matter, within the galaxy, is at a much lower density than the normal matter. Most of the dark matter is in a "halo" that surrounds the galaxy. This isn't to say it's more dense out there, it's just a statement that the normal matter collapses through friction to form the galaxy, while the dark matter more or less stays in its orbit at after it first becomes gravitationally bound to the galaxy.

So no, I don't think there would be much of an observable effect.

The closest thing to this suggestion that I've seen is that because of the fact that normal matter is so much more dense, it's going to attract some amount of dark matter to it. With more dark matter comes more annihilations (dark matter is expected to be made up of equal parts matter and anti-matter, because it must interact too weakly to have annihilated in the early universe to have the properties we observe). Dark matter annihilations are expected to be one observable signal we could potentially use to understand its properties.

One attempt at observing annihilating dark matter comes from WMAP observations:
http://arxiv.org/abs/0802.3830

At this point, I would place this observation of the WMAP haze at speculative at best. But at least it serves as a model of how one might go about observing dark matter directly.

I'm guessing Hawking work on radiation did not reflect any dark matter ingestion...but I wonder if it could be expanded/modified to do so.

I don't think it makes any difference whatsoever.

 

[heusdens]

Do black holes swallow dark matter

Only when they are on a diet.

 

[friend]

The problem is that the dark matter, within the galaxy, is at a much lower density than the normal matter. Most of the dark matter is in a "halo" that surrounds the galaxy. This isn't to say it's more dense out there, it's just a statement that the normal matter collapses through friction to form the galaxy, while the dark matter more or less stays in its orbit at after it first becomes gravitationally bound to the galaxy.

This is a question for me. Dark matter would orbit the center of mass. But since it does not interact much it would just pass to the other side without interaction. I have to think, though, that there would still be a much greater density of DM at the center than at the edges simply because the gravitational field is stronger there. Sure it would be traveling faster, but there would be more of it. Perhaps there could be a greate enough density of DM to form a BH.

 

[Chalnoth]

This is a question for me. Dark matter would orbit the center of mass. But since it does not interact much it would just pass to the other side without interaction. I have to think, though, that there would still be a much greater density of DM at the center than at the edges simply because the gravitational field is stronger there. Sure it would be traveling faster, but there would be more of it. Perhaps there could be a greate enough density of DM to form a BH.

Yes, the density of dark matter is expected to be larger near the galactic center. Not enough to make the density outweigh the normal matter, but still larger than it is outside the galaxy (if we define the galaxy as the normal matter part). As far as I'm aware, however, our observations of dark matter are not yet accurate enough to confirm this. But it is definitely expected from theory.

 

[Chronos]

Dark matter is not interactive with normal matter. It would pass right through a black hole. See the bullet cluster paper.

 

[Ich]

Dark matter is not interactive with normal matter. It would pass right through a black hole.

Huh?
Nothing passes right through a black hole.

 

[Vanadium 50]

Dark matter is not interactive with normal matter.

It gravitates (that's how we know it's there). It would therefore be captured by a BH in exactly the same way as normal matter.

 

[friend]

Yes, the density of dark matter is expected to be larger near the galactic center. Not enough to make the density outweigh the normal matter, but still larger than it is outside the galaxy (if we define the galaxy as the normal matter part). As far as I'm aware, however, our observations of dark matter are not yet accurate enough to confirm this. But it is definitely expected from theory.

If we have already established that DM can develop pockets of larger density when before it was an even distribution, then the question is why can't it become even denser and form BHs made only of DM. If it can become dense to begin with, then what's to stop it from becoming even denser?

 

[Chalnoth]

If we have already established that DM can develop pockets of larger density when before it was an even distribution, then the question is why can't it become even denser and form BHs made only of DM. If it can become dense to begin with, then what's to stop it from becoming even denser?

In principle it might, but the time scale for such a thing would be exceedingly long. The reasoning is as follows:

1. To form a black hole, you need a local overdensity of dark matter so great that it prevents the dark matter from escaping. The magnitude of this overdensity is vastly above the typical average density of dark matter within a galaxy or galaxy cluster.

2. In order to get such a massive overdensity, you need the orbits of the dark matter particles in a potential well to decay. This can only be done through friction.

3. Dark matter experiences almost no friction.

If you make the assumption of perfectly non-interacting dark matter, I'm sure you could calculate just how long this would take. Given our observations, this time scale must be many times the current age of the universe (because if it weren't, dark matter would have collapsed noticeably by now: it hasn't).

However, this may well turn out not to work for real dark matter, because real dark matter is likely to have some interaction. In particular, it is likely to be nearly equal parts matter and anti-matter, meaning that any significant overdensity of dark matter will also be very efficient at causing the dark matter particles to annihilate, likely causing the structure to evaporate long before it gets dense enough to form a black hole.

 

[George Jones]

When normal matter collapses, it loses energy through radiation, which tends to hasten collapse. Dark matter doesn't do this. Consequently: 1) normal matter forms black holes more easily; 2) black holes present larger effective targets to normal matter than they do to dark matter.

A quote from Weinberg's new cosmology book:

Of course, eventually the perturbations in the matter density became strong enough for the linear approximation to break down, as shown vividly be the existence of stars and galaxies and galaxy clusters. It is believed that these structures were formed in a two-step process.¹ First, in regions where the density was a little larger than average, the cold dark matter and the baryonic matter together expanded more slowly than the universe as a whole, eventually reaching a minimum density and then recontracting. This scenario is discussed in section 8.2. If an overdense region was sufficiently large then as shown in 8.3 its baryonic matter collapsed along with its cold dark matter. Then in a second stage, after this collapse, the baryonic matter lost its energy through radiative cooling, and it condensed protogalaxies consisting of clouds of gas that eventually form stars. The cold dark matter particles could not lose their energy through radiative cooling, so they remained in large more-or-less spherical halos around these galaxies.

¹S. D. M. White and M. J. Rees, Mon. Mot. Roy. Astron. Soc. 183 341 (1978)

[EDIT]Chalnoth posted much the same stuf while I was composing my post.[/edit]

 

[Chalnoth]

By the way, as a potential point of interest, even without any interactions (other than gravity), dark matter particle orbits will still decay over very long time scales. The argument goes as follows:

1. From time to time, dark matter particles will have close interactions with other dark matter particles that exchange energy between them. This means that the particles of dark matter in a potential well will be thermalized: their energy distribution will approach a thermal distribution with time.

2. A thermal distribution has a high-energy tail of particles that have enough velocity to escape the potential well. Thus the particles in the high-energy tail of the thermal distribution are always escaping. Since it is the highest-energy particles that escape, the average energy per particle is reduced in this process, meaning that it causes the cloud to collapse.

I do not know if this effect or the (weak) non-gravitational dark matter interactions turn out to be the dominant effect in controlling the long time scale behavior of dark matter.

 

[Chronos]

See:
Greedy Supermassive Black Holes Dislike Dark Matter
http://www.universetoday.com/13091/greedy-supermassive-black-holes-dislike-dark-matter/

Astronomers Find Black Holes Do Not Absorb Dark Matter
http://www.universetoday.com/60422/astronomers-find-black-holes-do-not-absorb-dark-matter/

 

[Chalnoth]

See:
Greedy Supermassive Black Holes Dislike Dark Matter
http://www.universetoday.com/13091/greedy-supermassive-black-holes-dislike-dark-matter/

Astronomers Find Black Holes Do Not Absorb Dark Matter
http://www.universetoday.com/60422/astronomers-find-black-holes-do-not-absorb-dark-matter/

Those headlines seem to be a bit misleading. The only thing that was found, as near as I can tell from reading the articles, is that the density of dark matter in the vicinity of black holes is not large enough to produce runaway accretion of dark matter into the black hole.

 

[Chronos]

These studies assert dark matter comprises a miniscule amount of the mass of black holes. Quoting from page 6 of arXiv:0802.2041v1:

" . . . We found that dark matter contributes to no more than 10% of the total mass accreted by black hole seeds."

This is the conservative upper limit and suggests black holes tend not to absorb dark matter, hence the headlines.

 

[Ich]

This is exactly what has been said in this thread: DM is less readily absorbed by black holes because it can't form accretion disks. It contradicts the claim that DM "would pass right through a black hole".

 

[Chronos]

The dark matter component of black holes appears to be vanishingly small, or nonexistent. It may be that dark matter does not accrete and just slides by, or that it simply passes through black holes. The properties of dark matter are not understood, nor is it necessarily bound to our present understanding of the laws of physics.

 

[Ich]

The properties of dark matter are not understood, nor is it necessarily bound to our present understanding of the laws of physics.

It is bound to gravitate. That's how we know about it.
So no, it will not pass through a black hole. No way.

 

[friend]

The dark matter component of black holes appears to be vanishingly small, or nonexistent. It may be that dark matter does not accrete and just slides by, or that it simply passes through black holes. The properties of dark matter are not understood, nor is it necessarily bound to our present understanding of the laws of physics.

If DM particles passed through BHs, then I think that would prove that it is not a particle at all subject to following the curvature of spacetime.

 

[Chalnoth]

If DM particles passed through BHs, then I think that would prove that it is not a particle at all subject to following the curvature of spacetime.

...which would indicate that they couldn't cluster, which would be incompatible with our observations.

 

[Saul]

The dark matter component of black holes appears to be vanishingly small, or nonexistent. It may be that dark matter does not accrete and just slides by, or that it simply passes through black holes. The properties of dark matter are not understood, nor is it necessarily bound to our present understanding of the laws of physics.

Guessing is not science. Compare hypothesis to hypothesis, hypothesis to observations. Logic analysis (pros/cons of each hypothesis) as opposed to picking a hypothesis and force feeding the observations to the chosen hypothesis.

It is a mistake to discard any reasonable hypothesis, however, if the "laws of physics" must be changed to make a hypothesis work that should be reason to consider other explanations.

AGN and QSO Super Massive "Black holes" have a maximum mass of approx. 3 x 10^9 solar masses. (That is one of the observations that requires an explanation.)

There is currently no explanation for the 3 x 10^9 solar mass BH limit observation. Galactic mergers in addition to dark matter would if "black holes" are classic black holes have created black holes in excess of 3 x 10^9 solar masses. (i.e. As noted because dark matter has not been detected and because there are observations such as the spiral galaxy rotation velocity variance with radius that is not in accordance with simulations that use the dark matter hypothesis, it possible that dark matter does not exist. Even if dark matter does not exist, normal matter would have created SMBHs in excess of 3 10^9 solar masses due to galaxy mergers based on statistical analysis of the number of mergers with time and the mass of SMBH merging.)

Here are other related observations that might help to provide a guide to the solution. (Think about Disney's finding that spiral galaxy parameters (luminosity, rotation velocity, and mass) are controlled (non-random) which indicates there is a single unknown parameter/mechanism that is controlling the spiral galaxy.

There is the problem of how to explain why spiral galaxies have not become elliptical galaxies due to mergers.

There is evidence of bimodal emission of spiral galaxies. The bimodal emission mechanism appears to be related what causes star burst galaxies.

We need a thread summarizing QSO observations.

The QSO spectrum is non-thermal generated. There are peculiar QSO emission structures (i.e. What moves matter in peculiar locations around the QSO and what causes it to emit in those locations?). QSO emission shows unexplained long term (periodic variation continues throughout the observation period, 30 years) periodic variance. 10% of QSO are naked quasars, which have the narrow region emission, but do not exhibit broad line region (BLR) emission (BLR is believed to due to emission from an accretion disk). The point is the QSOs in question do not have an accretion disk and are by some other mechanism causing the narrow line emission.

In the vicinity of our galaxy's SMBH there are peculiar paradox of youth stars. (Short lived very large stars located very close to galaxy's core.) These peculiar stars are OB very large stars which have peculiar orientations. (There are for example two strings of these supposedly OB stars in our galaxy that are orientated 90 degrees to each other with opposite rotations about the massive object at the center of our galaxy.)

There is the Holmberg effect. Satellite dwarf galaxies that orbit our galaxy and other spiral galaxies are aligned 90 degrees to the plane of the spiral galaxy.

There is the recent finding of Ultra Luminous x-ray sources in the vicinity of spiral galaxies's core.

Galactic clusters have anomalously hot intergalactic gas that is emitting x-rays. (10^7 K, very, very large structures). There is no explanation as to what could heat the cluster intergalactic gas to such high temperatures and there is no explanation as to why the cluster intergalactic gas has not cooled. The cluster intergalactic gas mass is roughly the same as the mass of the cluster's galaxies' mass.

http://arxiv.org/PS_cache/arxiv/pdf/1002/1002.0553v1.pdf

An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes

We study the growth rates of massive black holes in the centres of galaxies from accretion of dark matter from their surrounding haloes. By considering only the accretion due to dark matter particles on orbits unbound to the central black hole, we obtain a firm lower limit to the resulting accretion rate. We find that a runaway accretion regime occurs on a timescale which depends on the three characteristic parameters of the problem: the initial mass of the black hole, and the volume density and velocity dispersion of the dark matter particles in its vicinity. An analytical treatment of the accretion rate yields results implying that for the largest black hole masses inferred from QSO studies (> 10^9 Solar Mass), the runaway regime would be reached on time scales which are shorter than the lifetimes of the haloes in question for central dark matter densities in excess of 250M_ pc−3. Since reaching runaway accretion would strongly distort the host dark matter halo, the inferences of QSO black holes in this mass range lead to an upper limit on the central dark matter densities of their host haloes of _0 < 250M_ pc−3. This limit scales inversely with the assumed central black hole mass. However, thinking of dark matter profiles as universal across galactic populations, as cosmological studies imply, we obtain a firm upper limit for the central density of dark matter in such structures.

http://arxiv.org/abs/astro-ph/0501312v1

Ultra-luminous X-ray Sources in nearby galaxies from ROSAT HRI observations II. statistical properties

The statistical properties of the ultra-luminous X-ray source (ULX) populations extracted from the ROSAT HRI survey of X-ray point sources in nearby galaxies in Paper I are studied to reveal connections between the ULX phenomenon and survey galaxy properties.

This survey confirms statistically that the ULX phenomenon is closely connected to star formation activities, since ULXs preferentially occur in late-type galaxies rather than in early-type galaxies, and ULXs in late-type galaxies tend to trace the spiral arms. Only 5% of the early-type galaxies host ULXs above 1039 erg/sec, with 0.02±0.10 ULX per survey galaxy and −0.13±0.09 ULXs per 1010L⊙ that are consistent with being zeros. In contrast, 45% of the late-type galaxies host at least one ULX, with 0.72± 0.11 ULXs per survey galaxy and 0.84 ±0.13 ULXs per 1010L⊙. 70% of the starburst galaxies host at least one ULX, with 0.98±0.20 ULXs per survey galaxy and 1.5±0.29 ULXs per 10^10L. An increasing trend of the occurrence frequencies and ULX rates is revealed for galaxies with increasing star formation rates. Two ULX populations, the HMXB-like ULXs as an extension of the ordinary HMXB population associated with the young stellar population and the LMXB-like ULXs as an extension of the ordinary LMXB population associated with the old stellar population, are both required to account for the total ULX population.

 

[Chalnoth]

In the vicinity of our galaxy's SMBH there are peculiar paradox of youth stars. (Short lived very large stars located very close to galaxy's core.) These peculiar stars are OB very large stars which have peculiar orientations. (There are for example two strings of these supposedly OB stars in our galaxy that are orientated 90 degrees to each other with opposite rotations about the massive object at the center of our galaxy.)

There is the Holmberg effect. Satellite dwarf galaxies that orbit our galaxy and other spiral galaxies are aligned 90 degrees to the plane of the spiral galaxy.

I don't see why this is special. Likely just a matter of friction and/or tidal forces coupling the angular momenta. Or coincidence, in some cases.

There is the recent finding of Ultra Luminous x-ray sources in the vicinity of spiral galaxies's core.

I don't see how this could possibly highlight the nature of dark matter, as it's most likely radiation from the accretion disk around the galaxies' central black holes.

Galactic clusters have anomalously hot intergalactic gas that is emitting x-rays. (10^7 K, very, very large structures). There is no explanation as to what could heat the cluster intergalactic gas to such high temperatures and there is no explanation as to why the cluster intergalactic gas has not cooled. The cluster intergalactic gas mass is roughly the same as the mass of the cluster's galaxies' mass.

This, as far as I know, isn't a problem at all. The gas is heated by falling into the cluster's gravitational potential well. As it cools, it collects into either the existing galaxies within the cluster, or creates a new one. New gas falling into the cluster keeps the cluster gas hot.

 

[Saul]

As I said, there is an increasing set of observations that support the assertion that what we call a SMBH is a physical astrophysical object that can generate magnetic fields and that evolves with time.

There is due to how scientific ideas develop, are taught, and how difficult it is to change ones mind when a strong position has been taken, theoretical inertia which makes it difficult to even consider other explanations.


http://arxiv.org/PS_cache/arxiv/pdf/0912/0912.2040v1.pdf

The Spectral Energy Distribution of Fermi bright blazars

The results of this study lead to the conclusion that a simple homogeneous, one-zone, SSC model cannot explain the SED of the majority of the detected sources, especially of the LBL type (see Fig. 36). In addition, differential variability in the simultaneous optical and Xray data observed in IBL and HBL objects (that is close to the peak of the synchrotron component) suggests that multiple components are present in non LBL blazars (e.g., S5 0716+714, Giommi et al. 2008) as also clearly shown by simultaneous X-ray/TeV campaigns (e.g., PKS 2155-304, Aharonian et al. 2009). Our results also show that ERC models can easily fit the data as they can cover a very wide part of the parameter space of Fig. 36 (orange squares). However, models that are based on the presence of external radiation fields that are significantly different in FSRQs and BL Lacs, such as the broad-line region, accretion disk etc., must explain why a) the ratio of the number of FSRQs and BL Lacs of the LBL type (which have similar -ray spectral slopes and therefore are affected in the same way by the higher LAT sensitivity to hard sources) is similar in radio/microwave selected samples (e.g., 1 Jy, WMAP) and in the LBAS -ray selected sample, and b) why BL Lacs appear to show equal, or even larger, values of SSC peak (that is larger -ray excess above SSC) than FSRQs in Fig. 36. Finally, any emission model should explain why only less than 13% of bright radio sources (F > 0.5 Jy @ 1.4 GHz) of the LBL type are in the LBAS sample, while the other 87% with similar observational properties are below the LBAS detection threshold and may well be radiating close to simple SSC. We intend to address these topics in future papers.

 

[Saul]

Observations point in a theoretical direction.

http://arxiv.org/abs/astro-ph/0406163v1

Naked active galactic nuclei

In this paper we report the discovery of a new class of active galactic nucleus in which although the nucleus is viewed directly, no broad emission lines are present. The results are based on a survey for AGN in which a sample of about 800 quasars and emission line galaxies were monitored yearly for 25 years. Among the emission line galaxies was the expected population of Seyfert 2 galaxies with only narrow forbidden lines in emission, and no broad lines. However, from the long term monitoring programme it was clear that some 10% of these were strongly variable with strong continuum emission. It is argued that these objects can only be Seyfert 1 galaxies in which the nucleus is viewed directly, but in which broad emission lines are completely absent. We compare these observations with other cases from the literature where the broad line region is reported to be weak or variable, and investigate the possibility that the absence of the broad line component is due to reddening. We conclude that this does not account for the observations, and that in these AGN the broad line region is absent. We also tentatively identify more luminous quasars from our sample where the broad emission lines also appear to be absent. The consequences of this for AGN models are discussed, and a case is made that we are seeing AGN in a transition stage between the fuel supply from a surrounding star cluster being cut off, and the nucleus becoming dormant.

http://arxiv.org/abs/astro-ph/0509433

Discovery of a bright quasar without a massive host galaxy

Quasars are thought to be powered by the infall of matter onto a supermassive black hole at the centre of massive galaxies1,2. As the optical luminosity of quasars exceeds that of their host galaxy, disentangling the two components can be difficult. This led in the 1990’s to the controversial claim of the discovery of 'naked' quasars3–7. Since then, the connection between quasars and galaxies has been well established8. Here we report on the observation of a quasar lying at the edge of a gas cloud, whose size is comparable to that of a small galaxy, but whose spectrum shows no evidence for stars. The gas cloud is excited by the quasar itself.

If a host galaxy is present, it is at least six times fainter than would normally be expected8,9 for such a bright quasar. The quasar is interacting dynamically with a neighbouring galaxy – which matter might be feeding the black hole.

 

[Saul]

I don't see why this is special. Likely just a matter of friction and/or tidal forces coupling the angular momenta. Or coincidence, in some cases.I don't see how this could possibly highlight the nature of dark matter, as it's most likely radiation from the accretion disk around the galaxies' central black holes.This, as far as I know, isn't a problem at all. The gas is heated by falling into the cluster's gravitational potential well. As it cools, it collects into either the existing galaxies within the cluster, or creates a new one. New gas falling into the cluster keeps the cluster gas hot.

These anomalies each deserve their own thread to explain why they are anomalies. You have an immediate answer but you have not seen the observations and related analysis.

There is no logic reason why the first developed hypothesis is the correct hypothesis. It appears that it is very difficult for people to even think about competing hypotheses. It seems people cannot think hypothetically. After a period of time theories appear to become written in stone. People seem very convinced that the massive object is a classical BH and are viewing all the observations from that theoretical viewpoint. There seems to be a mental block to consider other hypotheses.

What is required for this thread is an explanation as to why SMBH have a mass limit which is one of the anomalies that requires explanation.

It suggested the answer to that question requires an answer to what is the massive object in the center of the galaxies and how it evolves. Matter goes into the SMBH. Can it come out?

Is there any observational evidence that supports the assertion that matter comes out of the SMBH? Evidence of periodic variation of emission from the massive object for instance. If there is, what force is causing ejection of the matter from the SMBH? The point is there must be a build up and release.

It seems there are observations that support the assertion that the SMBH is a physical object that evolves, not a classical BH that can only emit due to its accretion disk.

Rather than agreeing or disagreeing with that statement, I suggest that we can view the observations from the standpoint of the different hypotheses, a dynamic massive object and classical BH model and then look for observations to support or refute either hypothesis.

 

[Chalnoth]

As I said, there is an increasing set of observations that support the assertion that what we call a SMBH is a physical astrophysical object that can generate magnetic fields and that evolves with time.

And this is different from a black hole how, exactly?

 

[Chalnoth]

What is required for this thread is an explanation as to why SMBH have a mass limit which is one of the anomalies that requires explanation.

Sorry, but that's actually pretty off topic for the thread.

 

[Saul]

Sorry, but that's actually pretty off topic for the thread.

Sorry, back to the question at hand.

If dark matter exists there must be an explanation as to why the super massive object does not continue to grow due to dark matter in fall.

Possible 1: Dark matter does not exist.

What is your answer?

http://arxiv.org/abs/astro-ph/0405393v1

On the cosmological Evolution of Quasar Black Hole Masses

Virial black-hole mass estimates are presented for 12698 quasars in the redshift interval 0.1 ≤ z ≤ 2.1, based on modelling of spectra from the Sloan Digital Sky Survey (SDSS) first data release . The black-hole masses of the SDSS quasars are found to lie between ≃ 107 M⊙ and an upper limit of ≃ 3 10^9 solar M, entirely consistent with the largest black-hole masses found to date in the local universe. The estimated Eddington ratios of the broad-line quasars (FWHM≥ 2000 km s−1) show a clear upper boundary at Lbol/LEdd ≃ 1, suggesting that the Eddington luminosity is still a relevant physical limit to the accretion rate of luminous broadline quasars at z ≤ 2. By combining the black-hole mass distribution of the SDSS quasars with the 2dF quasar luminosity function, the number density of active black holes at z ≃ 2 is estimated as a function of mass. By comparing the estimated number density of active black holes at z ≃ 2 with the local mass density of dormant black holes, we set lower limits on the quasar lifetimes and find that the majority of black holes with mass ≥ 108.5 M⊙ are in place by ≃ 2.

 

[Saul]

And this is different from a black hole how, exactly?

I will start a separate thread to discuss.

 

[Chalnoth]

Sorry, back to the question at hand.

If dark matter exists there must be an explanation as to why the super massive object does not continue to grow due to dark matter in fall.

This was already answered by one of the papers you cited (and was also cited earlier in this thread): dark matter infall won't be significant unless the local density of dark matter is above some threshold value. Clearly the dark matter isn't that dense in the galactic core. What more needs to be said?

Possible 1: Dark matter does not exist.

What is your answer?

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

Bam.

 

[Saul]

This was already answered by one of the papers you cited (and was also cited earlier in this thread): dark matter infall won't be significant unless the local density of dark matter is above some threshold value. Clearly the dark matter isn't that dense in the galactic core. What more needs to be said?


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

Bam.

1) How does one keep the dark matter from clustering around the super massive object? It appears dark matter works in one direction only. (i.e. It is invoked when required to explain anomalous motion and must cluster to explain the anomalous motion. It does not cluster around super massive black holes.)

2) See thread in astrophysics section "Dark matter on the ropes?" I agree the explanation for the anomalous motion is not MOND.

 

[Chalnoth]

1) How does one keep the dark matter from clustering around the super massive object? It appears dark matter works in one direction only. (i.e. It is invoked when required to explain anomalous motion and must cluster to explain the anomalous motion. It does not cluster around super massive black holes.)

It's nearly frictionless, so it has no mechanism to cluster significantly around a supermassive black hole.

2) See thread in astrophysics section "Dark matter on the ropes?" I agree the explanation for the anomalous motion is not MOND.

It's not just about anomalous motion. Today, a wide body of mutually-corroborating evidence all points towards dark matter.

 

[Saul]

It's nearly frictionless, so it has no mechanism to cluster significantly around a supermassive black hole.


It's not just about anomalous motion. Today, a wide body of mutually-corroborating evidence all points towards dark matter.

The cuspy halo problem is that dark matter density should increase around mass centers such as super massive black holes. If the super massive object is a classical BH it will continue to grow if dark matter in falls into it.

Yes or No? If No explain why it does not.

The paper I quoted has no mechanism to avoid dark matter clustering and super massive black hole uncontrolled growth. Dark matter must interact with matter via gravity. The authors state a maximum density for dark matter in the vicinity of super massive black hole.

What you are missing when you state dark matter does not form cusps, is if it does not form cusps it will also not form halos about galaxies.

As there appears to be no physical explanation for why dark matter does not form cusps, the hypothesis that super massive black hole is a physical object that can evolve and change as opposed to a classic BH appears to be viable. My point is there is observation evidence of ejection from the massive object. (I will start a separate thread to discuss.)

As to whether dark matter does or does not exist, the thread "Dark Matter on the Ropes?" includes specific observations (the observed change in rotational velocity of spiral galaxies with radius and the number of satellite galaxies that form around a spiral galaxy for example.) which are not in agreement with the dark matter hypothesis. The correct hypothesis must explain all observations. The fact that the dark matter hypothesis does not explain all observation is indication that something is fundamentally incorrect with the hypothesis.

From the standpoint of solving the problem it is better to have no explanation than an incorrect hypothesis.

As I stated MOND also cannot explain the observations.

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

The cuspy halo problem arises from cosmological simulations that seem to indicate cold dark matter would form cuspy distributions — that is, increasing sharply to a high value at a central point — in the most dense areas of the universe. This would imply that the center of our galaxy, for example, should exhibit a higher dark-matter density than other areas. However, it seems rather that the centers of these galaxies likely have no cusp in the dark-matter distribution at all.

This remains an intractable problem. Speculation that the distribution of baryonic matter may somehow displace cold dark matter in the dense cores of spiral galaxies has not been substantiated by any plausible explanation or computer simulation.

 

[Chalnoth]

The cuspy halo problem is that dark matter density should increase around mass centers such as super massive black holes. If the super massive object is a classical BH it will continue to grow if dark matter in falls into it.

There are two problems with your presumptions:
1. Simulations aren't very good at modeling baryonic matter, and the "cuspy halo problem" is critically dependent upon the baryon matter model.
2. Because we currently don't know how dark matter interacts, simulations ignore any interactions that dark matter does have. For instance, a small annihilation cross section may easily solve the "cuspy halo problem" because dark matter annihilations could prevent high density regions from forming.

It is not reasonable to throw out dark matter when simply implementing expected non-idealities of dark matter may well solve the "cuspy halo problem".

 

[Chronos]

Dark matter survives these issues when it is resistant to accretion by black holes [links already provided]. It strongly suggests dark matter either does not exist [unlikely], or has properties not yet understood. The fact that eddington [and mass] limits are obeyed in all suspected black holes observed to date is not insignificant.

 

[Saul]

There are two problems with your presumptions:
1. Simulations aren't very good at modeling baryonic matter, and the "cuspy halo problem" is critically dependent upon the baryon matter model.
2. Because we currently don't know how dark matter interacts, simulations ignore any interactions that dark matter does have. For instance, a small annihilation cross section may easily solve the "cuspy halo problem" because dark matter annihilations could prevent high density regions from forming.

It is not reasonable to throw out dark matter when simply implementing expected non-idealities of dark matter may well solve the "cuspy halo problem".

The are two problems with what you are proposing. The first is why would dark matter annihilate itself? The second is when the universe was formed there would be high density and all the dark matter would annihilate itself.

 

[Saul]

Dark matter survives these issues when it is resistant to accretion by black holes [links already provided]. It strongly suggests dark matter either does not exist [unlikely], or has properties not yet understood. The fact that eddington [and mass] limits are obeyed in all suspected black holes observed to date is not insignificant.

To explain the observations the Dark matter hypothesis requires a smart particle that changes it properties to resolve the paradoxes. The dark matter hypothesis appears to be in trouble.

What is required is a mechanism to stop dark matter from forming cusps in the center of galaxies. The dark matter will in fall into the super massive object if dark matter exists, however, if the density of the dark matter particles at the center of the galaxy is less the in fall of dark matter into the SMBH will not cause the galaxy to collapse on itself, in the period of the universe's life to date. Eventually, the galaxy will however collapse on itself. Reducing the density of dark matter only delays the collapse.

This paper hypotheses that dark matter is a smart particle "BDM" that changes its properties to resolve the paradox. At high density BDM has no mass and moves at the speed of light due to quantum interactions of BDM to BDM particle . At low density BDM is a massive particle.

What is required is a dark matter halo that reaches a maximum density, hence the need for the smart Dark matter particle. i.e. bimodal dark matter "BDM".

http://arxiv.org/PS_cache/arxiv/pdf/0908/0908.0571v1.pdf

BDM Dark Matter: CDM with a core profile and a free streaming scale

We present a new dark matter model BDM which is an hybrid between hot dark matter HDM and cold dark matter CDM, in which the BDM particles behave as HDM above the energy scale Ec and as CDM below this scale. Evolution of structure formation is similar to that of CDM model but BDM predicts a nonvanishing free streaming _fs scale and a inner galaxy core radius rcore, both quantities determined in terms of a single parameter Ec, which corresponds to the phase transition energy scale of the subjacent elementary particle model. For energies above Ec or for a scale factor a smaller then ac, with a < ac < aeq, the particles are massless and _ redshifts as radiation. However, once the energy becomes E ≤ Ec or a > ac then the BDM particles acquire a large mass through a non perturbative mechanism, as baryons do, and _ redshifts as matter with the particles having a vanishing velocity. Typical energies are Ec = O(10 − 100)eV giving a _fs ∝ E−4/3 c < _Mpc and Mfs ∝ E−4 c < _ 109M⊙. A _fs 6= 0, rcore 6= 0 help to resolve some of the shortcomings of CDM such as overabundance substructure in CDM halos and numerical fit to rotation curves in dwarf spheroidal and LSB galaxies. Finally, our BDM model and the phase transition scale Ec can be derived from particle physics.

The model simply consist of particles that at high energy densities are massless relativistic particles with a velocity of light, v = c, but at low densities they acquire a large mass, due to nonperturbative quantum field effects, and become non relativistic with a vanishing (small) dispersion velocity. We will name this type of dark matter BDM, from bound states dark matter. The name is motivated by the particle physics model, discussed in section III, but we would like to stress out that the cosmological properties of BDM do not depend on this particle model but on the different behavior of the BDM particles. The phase transition energy density is defined pc ≡ E4 c and its value can be determined theoretical by the particle physics model or phenomenological by consistency with the cosmological data.

A large number of candidates have been proposed for DM of which cold dark matter (CDM) has been the most popular. CDM model has been successful on large scales in explaining structure formation in the early universe as well as abundances of galaxy clusters [1]. However, CDM predicts steeply cusped density profiles and causing a large fraction of haloes to survive as substructure inside larger haloes [4, 5]. These characteristics of CDM haloes, however, seem to disagree with a number of observations. The number of sub-haloes around a typical Milky Way galaxy, as identified by satellite galaxies, is an order of magnitude smaller than predicted by CDM [6] and the observed rotation curves for dwarf spheriodal dSph and low surface brightness (LSB) galaxies seem to indicate that their dark matter haloes have constant density cores [7, 8] instead of steep cusps as predicted by the NFW profile. Low surface brightness galaxies are diffuse, low luminosity systems, with a total mass believed to be dominated by their host dark matter halos [9]. Assuming that LSB galaxies are in dynamical equilibrium, the stars act as tracers of the gravitational potential, and can therefore be used as a probe of the dark matter density profile [10]. Much better fits to dSph and LSB observations are found when using a cored halo model [11]. Cored halos have a mass-density that remains at an approximately constant value towards the center.

 

[Chalnoth]

The are two problems with what you are proposing. The first is why would dark matter annihilate itself?

Because dark matter is weakly-interacting, it is unlikely to have the same matter/anti-matter asymmetry that baryonic matter has (the primordial asymmetry in baryonic matter/anti-matter was very small, but nearly all of it annihilated due to the fast reaction time of baryonic matter).

A majority of dark matter models, as a result, predict annihilation to occur (albeit slowly).

The second is when the universe was formed there would be high density and all the dark matter would annihilate itself.

The expansion rate dampens the annihilation. Given a particular model, it isn't that difficult to compute the expected abundance of dark matter. Yes, there is a parameter space where it all self-annihilates (a region of parameter space that is therefore excluded). But there is also substantial parameter space where there is self annihilation, but enough of it survives in the early universe for it to be as abundant as we observe today.

 

[Saul]

Because dark matter is weakly-interacting, it is unlikely to have the same matter/anti-matter asymmetry that baryonic matter has (the primordial asymmetry in baryonic matter/anti-matter was very small, but nearly all of it annihilated due to the fast reaction time of baryonic matter).

A majority of dark matter models, as a result, predict annihilation to occur (albeit slowly).The expansion rate dampens the annihilation. Given a particular model, it isn't that difficult to compute the expected abundance of dark matter. Yes, there is a parameter space where it all self-annihilates (a region of parameter space that is therefore excluded). But there is also substantial parameter space where there is self annihilation, but enough of it survives in the early universe for it to be as abundant as we observe today.

I do not see why dark matter would self annihilate when its density exceeds 250 Solar masses/pc^3. (The point is 250 solar masses/pc^3 is not a high density.) Think of baryonic matter in a star or a planet. Does it self annihilate?

However, setting aside the physics question of why dark matter would self annihilate at low densities, the self annihilation hypothesis appears to fail as the density of dark matter in the early universe would be higher than 250 Solar masses/pc^3, therefore all of the dark matter would have self annihilated.

The author's solution is as noted above to hypothesis bimodal dark matter where dark matter is hot dark matter (Moves at the speed of light) for densities that are greater than 250 solar masses/pc^3 and cold dark matter when the density of dark matter is less than 250 solar masses/pc^3.

http://arxiv.org/PS_cache/arxiv/pdf/1002/1002.0553v1.pdf

An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes

Since reaching runaway accretion would strongly distort the host dark matter halo, the inferences of QSO black holes in this mass range lead to an upper limit on the central dark matter densities of their host haloes of po (Dark matter density) < 250 solar masses/pc^3. This limit scales inversely with the assumed central black hole mass. However, thinking of dark matter profiles as universal across galactic populations, as cosmological studies imply, we obtain a firm upper limit for the central density of dark matter in such structures.

 

[Saul]

http://arxiv.org/PS_cache/arxiv/pdf/1001/1001.4691v3.pdf

If dark matter self annihilated when the dark matter density was at the modest 250 solar masses/pc^3 the self annihilation would have affected the CMB.

CMB data constraint on self-annihilation of dark matter particles

Recently, self-annihilation of dark matter particles is proposed to explain the “WMAP Haze” and excess of energetic positrons and electrons in ATIC and PAMELA results. If self-annihilation of dark matter occurs around the recombination of cosmic plasma, energy release from self-annihilation of dark matter delays the recombination, and hence affects CMB anisotropy. By using the recent CMB data, we have investigated the self-annihilation of dark matter particles. In this investigation, we do not found statistically significant evidence, and impose an upper bound on hvi/m. The upcoming data from Planck surveyor and the Fermi Gamma-ray telescope will allow us to break some of parameter degeneracy and improve constraints on self-annihilation of dark matter particles.

By analyzing the recent CMB data, we have constrained the self-annihilation of dark matter particles. We do not find statistically significant evidence on self-annihilation, and impose an upper bound on Fdm < 0.7314 at 95% confidence level. Due to the parameter degeneracy (i.e. Fdm hvi/m) in our analysis, significant self-annihilation is still possible, provided a dark matter particle is very massive (i.e. ≫1GeV). Therefore, a dark matter particle should be quite massive (i.e. m≫1GeV), if the excess of energetic positrons and electrons in PAMELA/ATIC data is attributed to self-annihilation of dark matter particles. Self-annihilation of dark matter particles leads to high level of gamma-ray emission from the region around the Galactic halo. Therefore, Fermi Gamma-ray telescope will allow us to break some of parameter degeneracy and impose independent constraints on self-annihilation of dark matter. Using the upcoming Planck data as well as Fermi Gammaray telescope data, we shall be able to impose important constraints on self-annihilation properties of dark matter particles.

 

[Chalnoth]

I do not see why dark matter would self annihilate when its density exceeds 250 Solar masses/pc^3. (The point is 250 solar masses/pc^3 is not a high density.) Think of baryonic matter in a star or a planet. Does it self annihilate?

Baryonic matter in a star is basically all normal matter. Obviously it can't annihilate. But due to the weak interactions of dark matter, those annihilations in the early universe would generally have been rather slow, leaving nearly equal parts matter and anti-matter around (if not exactly equal, as the asymmetry that produced the overabundance of normal matter for baryons wouldn't work for dark matter).

Anyway, if you want to see how this is computed, you can look in most any cosmology textbook about how the primordial neutrino abundance is computed. The calculation for most WIMP candidates is similar, just with a different set of parameters (mass, interaction strength, interaction turnoff temperature, etc.), and without the confounding factor of neutron/proton interactions. The physical process for self interaction becomes slow compared to the expansion rate before they all annihilate, and you're left with lots of matter/anti-matter laying around.

The point is, however, that the annihilation interaction never disappears entirely. It just becomes a low-probability interaction. But when you collect lots of dark matter in the same location, the number of close encounters between dark matter particles grows dramatically, and thus so does the self-annihilation rate.

However, setting aside the physics question of why dark matter would self annihilate at low densities, the self annihilation hypothesis appears to fail as the density of dark matter in the early universe would be higher than 250 Solar masses/pc^3, therefore all of the dark matter would have self annihilated.

This density is about 1.7*10^9 times the current critical density. Thus the dark matter would have been around this dense at around a redshift of z=2000, when the universe was a mere 133,000 years old. So the annihilation rate only needs to be slow enough that it would have taken longer than a few hundred thousand years or so to annihilate at those densities (possibly less, depending: the primordial abundance could have been very very high).

But if it takes a few hundred thousand years to annihilate, that should be well within the range to solve the cuspy halo problem.

 

[Saul]

Dark Matter Self Annihilation is invoked to:

1) Limit the density of dark matter in the vicinity of super massive black holes (SMBH), to limit the growth of SMBHs. A classical BH has no mechanism to eject matter/mass/energy. (Hawkings radiation besides being undetected is not a theoretical solution.) Dark matter or matter that in falls into the SMBH will cause the SMBH to continue to gain mass with time. That is not observed. SMBH have a maximum mass of around 3 x 10^9 solar masses.
2) To limit the density of dark matter in the center of galaxies to explain the galaxy inner core rotational problem. (Simulations show the galaxy rotation velocity in the inner core of the galaxy should vary as 1/r where observations indicated the rotational velocity of galaxies varies as r in the inner core of galaxies.)
3) Explain the cluster intergalactic gas heating problem. (The temperature of intergalactic gas in the center of clusters is roughly 10^7 k. There are two problems. What heats the cluster intergalactic gas? And why does the cluster intergalactic gas not cool? There is also a third interesting problem, what is the source of the cluster intergalactic gas. The mass of the cluster intergalactic gas is roughly the same as the mass of all stars in the cluster.)

To prove or disprove the hypothesis that Dark Matter self annihilates one can look for dark matter self annihilation products.

The detection of dark matter self annihilation products is currently negative.

http://arxiv.org/PS_cache/arxiv/pdf/1002/1002.2239v4.pdf

Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope

Nearby clusters and groups of galaxies are potentially bright sources of high-energy gamma-ray emission resulting from the pair-annihilation of dark matter particles. However, no significant gamma-ray emission has been detected so far from clusters in the first 11 months of observations with the Fermi Large Area Telescope. We interpret this non-detection in terms of constraints on dark matter particle properties. In particular for leptonic annihilation final states and particle masses greater than 200 GeV, gamma-ray emission from inverse Compton scattering of CMB photons is expected to dominate the dark matter annihilation signal from clusters, and our gamma-ray limits exclude large regions of the parameter space that would give a good fit to the recent anomalous Pamela and Fermi-LAT electron-positron measurements. We also present constraints on the annihilation of more standard dark matter candidates, such as the lightest neutralino of supersymmetric models. The constraints are particularly strong when including the fact that clusters are known to contain substructure at least on galaxy scales, increasing the expected gamma-ray flux by a factor of 5 over a smooth-halo assumption. We also explore the effect of uncertainties in cluster dark matter density profiles, finding a systematic uncertainty in the constraints of roughly a factor of two, but similar overall conclusions. In this work, we focus on deriving limits on dark matter models; a more general consideration of the Fermi-LAT data on clusters and clusters as gamma-ray sources is forthcoming.

Clusters of galaxies are the most massive collapsed objects in the Universe and are very dark matter dominated, making them potentially bright sources of gamma-ray emission from dark matter annihilation. No significant gamma-ray emission has been detected from clusters of galaxies in the first 11 months of Fermi-LAT survey mode observations [10]. In this paper, we explored the implications of the non-detection of clusters by Fermi-LAT in terms of constraints on models of dark matter annihilation. In particular, we focused on the six best candidate clusters and groups of galaxies in the context of searches for gamma-ray emission from dark matter pair annihilation [2] after excluding from the sample clusters which host bright central AGN or lie close to the Galactic plane. We analyzed the Fermi-LAT data to derive upper limits on the gamma-ray flux from dark matter annihilation in specific models, self-consistently incorporating the expected spectral shape for a given particle mass and annihilation final state. We conservatively assume only gamma-ray emission from dark matter annihilation when interpreting the ...

 

[Saul]

Dark matter if it exists, should theoretically interact with itself and should form clusters.

If dark matter forms clusters the clusters should show evidence of self annihilation. (See comment above as to why dark matter self annihilation is theoretically required to explain observations, via the dark matter hypothesis.)

http://www.nature.com/nature/journal/v433/n7024/abs/nature03270.html

Earth-mass dark-matter haloes as the first structures in the early Universe

The Universe was nearly smooth and homogeneous before a redshift of z = 100, about 20 million years after the Big Bang1. After this epoch, the tiny fluctuations imprinted upon the matter distribution during the initial expansion began to collapse because of gravity. The properties of these fluctuations depend on the unknown nature of dark matter2, 3, 4, the determination of which is one of the biggest challenges in present-day science5, 6, 7. Here we report supercomputer simulations of the concordance cosmological model, which assumes neutralino dark matter (at present the preferred candidate), and find that the first objects to form are numerous Earth-mass dark-matter haloes about as large as the Solar System. They are stable against gravitational disruption, even within the central regions of the Milky Way. We expect over 10^15 to survive within the Galactic halo, with one passing through the Solar System every few thousand years. The nearest structures should be among the brightest sources of γ-rays (from particle–particle annihilation).

 

[Chalnoth]

Given that our observations of dark matter annihilation are in their infancy, it's not really much of a surprise that we have yet to definitively detect such annihilation products. It will be a little while before we begin to explore an interesting fraction of the available dark matter parameter space.

 

[Chronos]

Dark matter interacts about as often as centegenarians have torrid extramarital affairs. We have all manner of very sensitive devices designed to detect dark matter annihilations, and it remains very shy.

 

[Radrook]

Huh?
Nothing passes right through a black hole.

There are theoretical speculations that propose just such a thing. The material coming out the other end of the black hole is called a white hole!

White Holes
http://www.astronomycafe.net/qadir/q1470.html