The universe is crowded with black holes

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  • Thread starter wolram
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  • #1
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Main Question or Discussion Point

I am not sure if this is true, if it is can these black holes be the dark matter we have been searching for.

June 22, 2016
Rochester Institute of Technology
Astronomers have presented one of the most complete models of matter in the universe and predict hundreds of massive black hole mergers each year observable with the second generation of gravitational wave detectors.

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  • #2
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BH's have been suggested as DM before, they would be a form of MACHO.

It is generally thought that not enough micro-lensing events have been observed to verify the existence of such objects. However there is a window of possible mass for IMBHs in which their larger masses would require a low enough number density so that detections becomes too infrequent.

Another problem would be to develop an IMF that would dump most mass in massive black holes rather than stars, but perhaps PopIII remnants may provide them.

Now we are in the epoch of gravitational wave astronomy perhaps the detection rate of BH mergers will show more such objects actually exist in which case we will have to think again!

  • #3
Staff Emeritus
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I am not sure if this is true, if it is can these black holes be the dark matter we have been searching for.
As far as I know, no, they can't. The distribution would be different from what we currently observe, and you'd need enough black holes to account for several times the mass of observable matter. It should be easy to detect these black holes if there were so many, but we do not.
  • #4
Science Advisor
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The gamma ray background excludess all but large black holes as DM candidates. See for discussion. Your cited article basically acknowledges this fact, but fails to account for the deficiency in microlensing events expected from a large population of massive black holes.
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