Astronomers Find Black Holes Do Not Absorb Dark Matter

by Nancy Atkinson on March 22, 2010

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Artist’s schematic impression of the distortion of spacetime by a supermassive black hole at the centre of a galaxy. The black hole will swallow dark matter at a rate which depends on its mass and on the amount of dark matter around it. Image: Felipe Esquivel Reed.

There’s the common notion that black holes suck in everything in the nearby vicinity by exerting a strong gravitational influence on the matter, energy, and space surrounding them. But astronomers have found that the dark matter around black holes might be a different story. Somehow dark matter resists ‘assimilation’ into a black hole.

About 23% of the Universe is made up of mysterious dark matter, invisible material only detected through its gravitational influence on its surroundings. In the early Universe clumps of dark matter are thought to have attracted gas, which then coalesced into stars that eventually assembled the galaxies we see today. In their efforts to understand galaxy formation and evolution, astronomers have spent a good deal of time attempting to simulate the build up of dark matter in these objects.

Dr. Xavier Hernandez and Dr. William Lee from the National Autonomous University of Mexico (UNAM) calculated the way in which the black holes found at the center of galaxies absorb dark matter. These black holes have anything between millions and billions of times the mass of the Sun and draw in material at a high rate.

The researchers modeled the way in which the dark matter is absorbed by black holes and found that the rate at which this happens is very sensitive to the amount of dark matter found in the black holes’ vicinity. If this concentration were larger than a critical density of 7 Suns of matter spread over each cubic light year of space, the black hole mass would increase so rapidly, hence engulfing such large amounts of dark matter, that soon the entire galaxy would be altered beyond recognition.

“Over the billions of years since galaxies formed, such runaway absorption of dark matter in black holes would have altered the population of galaxies away from what we actually observe,” said Hernandez

Their work therefore suggests that the density of dark matter in the centers of galaxies tends to be a constant value. By comparing their observations to what current models of the evolution of the Universe predict, Hernandez and Lee conclude that it is probably necessary to change some of the assumptions that underpin these models – dark matter may not behave in the way scientists thought it did.

There work appears in the journal Monthly Notices of the Royal Astronomical Society.

The team’s paper can be found here.


Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Lawrence B. Crowell March 24, 2010 at 3:41 PM

@ GrahamC: Yes the mass from DM does re-emerge in Hawking radiation. The black hole will emit most of this radiation in the form of photons. It is only until the BH gets to subatomic sizes (after a huge amount of time ~ 10^{70} to 10^{100} years) that Hawking radiation reflects the spectra of elementary particles in the radiation emitted. This would include DM as well. I just worked out a scheme where there is a quantum critical point with extremal black holes which turn out to have the (8,1) representation or spectra of the E_8 group.

@ Hon. Salacious B. Crumb: The cold neutrino theory was popular in the early 1990s or so. I remember a DPF conference where there was a flurry of such papers presented around that time. I even had a beer with a guy who was into this. The problem with this idea, which in part explains why it is not upheld by many any more, is that the neutrino mass matrix (Pontecorvo–Maki–Nakagawa–Sakata matrix) with the super-Kamiokande data gives ~10-100ev for the neutrino masses. This turns out to be too small to account for DM, and further for it to exist in clouds the kinetic energy of these particles must be very small ~ milli-ev range. So they do not turn out to be a workable component of cold DM.


wjwbudro March 26, 2010 at 1:39 PM

I always envisioned, based on some interpretations of observation, that DM seems to be a sort of incubator or cocoon in which the baryonic plasma cooled and began galaxy/cluster formation. It would therefor be out of reach of the BH influence. Well, it does stand to reason, don’t it?

Hannes March 27, 2010 at 10:33 AM

Why did you remove all my remarks?

wjwbudro March 27, 2010 at 1:39 PM

You mentioned Higgs in the same breath as photon, Z^0 supersymmetry. Are you suggesting that DM is a force rather than a particle. Interesting. Maybe the DM influence is a force acting in concert with gravity that gives rise to the large scale matter structure similar to what is speculated at the QM level.
What if the LHC finds it? Will this influence cosmology?I know I’m late here but, damn this is fascinating stuff to ponder, even for a non-scientist.

Kawarthajon March 29, 2010 at 6:54 AM

Torbjorn Larsson OM:

Thanks for your comments about my misunderstanding of the article in question, but forgive my misunderstanding when the TITLE of the article reads: Astronomers Find Black Holes Do Not Absorb Dark Matter.

I don’t have a back ground in physics and I’ve never actually taken a physics course – not even in high school – but I am very curious about astronomy and try to read as much about it as I can. I don’t understand any of the comments you made to correct my misunderstanding because of my lack of science background.

utopia27 April 1, 2010 at 12:07 AM

thank you LID and Jason Kurant. I’ve been considering for some time that M theory might be the right way to explain DM. I’ve run it past a few people, and not gotten much encouragement. Now at least I know there’s _someone_ else that thinks this is a plausible explanation.

This speculation about results of DM incorporation into BHs may yield some testable hypotheses for M theory, as well as some particular parameter estimates for the notoriously prolific (and non-testable) constants inherent in string and related theories.

If we assume that DM resides on a (series of ) different brane(s), then it is specifically non-interacting with matter on our brane. However, each brane can interact with matter in its brane – leading to potential friction and clumping of matter surrounding our-brane BHs. The size of the flat-density DM region surrounding black holes may give us a way to estimate the per-brane density of matter, and it may also give us a means to estimate the cross-brain falloff in gravity (and thus potentially the dimensional length of dimensions propagating gravity). These two estimates will probably be linked.

Observations of diverse-sized BHs and surrounding DM density may give us enough data to disentangle cross-brane propagation v. matter density per brane.

Unfortunately, that’s where I run out of ideas. I’m not a trained physicist/cosmologist, and don’t have the framework to set up the equations.

OvidAmongtheGoths May 23, 2011 at 7:12 AM

This is powerful evidence that Dark Matter does not exist. First it was postulated that dark matter only interacted gravitationally. But if it resists “assimilation” into a black hole, it is not obeying gravitational laws. If real, it could pass through a star’s heart and escape by flying on through without interacting. But nothing may do this if it passes inside the event horizon of a black hole UNLESS it is travelling faster than light.

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