Does Dark matter get trapped in black holes and increase their mass?

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Main Question or Discussion Point

Dark matter passes through everything, but is only influenced by gravity, so in the case of a neutron star, since dark matter doesn't interfere with ordinary matter, it can just pass through it, but neutrinos might be stopped by it's density, as neutrinos can just pass through stars almost as if they don't exist. The problem is black holes,
1. Does dark matter get trapped in black holes and increase it's mass
2. Does dark matter pass through it as if it doesn't even exist? it gets accelerated into the black hole's event horizon faster than the speed of light by it's gravity, then, passes through it and comes out of the event horizon on the other side?, but astrophysicists say nothing can come out of a event horizon.
 

Answers and Replies

  • #2
phinds
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1. Does dark matter get trapped in black holes and increase it's mass
Yes. NOTHING can escape a BH once it goes past the event horizon
2. Does dark matter pass through it as if it doesn't even exist? it gets accelerated into the black hole's event horizon faster than the speed of light
Nothing travels faster than c, so you have a misunderstanding here.
 
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  • #3
Bandersnatch
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Does dark matter get trapped in black holes and increase it's mass
Yes, the hypothetical particles must obey general relativity too.
 
  • #4
PAllen
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Also, dark matter may well be captured by neutron stars. Very weakly interacting does not mean no interaction, and neutron stars are exceedingly dense. If dark matter can occasionally interact weakly with a neutron star, it can be gravitationally captured. See the following for consequences of various assumptions:

https://arxiv.org/abs/1201.2400
 
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  • #5
phinds
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Also, dark matter may well be captured by neutron stars. Very weakly interesting does not mean no interaction, and neutron stars are exceedingly dense. If dark matter can occasionally interact weakly with a neutron star, it can be gravitationally captured. See the following for consequences of various assumptions:
Personally, I find DM to be more than very weakly interesting. :oldlaugh:
 
  • #6
Ibix
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Does dark matter pass through it as if it doesn't even exist? it gets accelerated into the black hole's event horizon faster than the speed of light by it's gravity, then, passes through it and comes out of the event horizon on the other side?,
As others have noted, this is not how it works. Essentially a black hole is a region of spacetime that is "shaped" (not quite the right word, but it'll do) so that there are no paths leading back across the event horizon. Thus it doesn't matter if incoming particles interact with other matter or not (edit: and GR doesn't have matter anywhere inside the hole anyway) - once they are in there is no route out.
 
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  • #7
PAllen
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Personally, I find DM to be more than very weakly interesting. :oldlaugh:
Fixed
 
  • #8
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Yes. NOTHING can escape a BH once it goes past the event horizonNothing travels faster than c, so you have a misunderstanding here.
Right, I was thinking about the concept of digging a hole through a uniform sphere planet's axis with no atmosphere and doping a ball through it, it comes out the other side the same force it enters in with, that couldn't work with black holes though as it breaks the light limit.
 
  • #9
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As others have noted, this is not how it works. Essentially a black hole is a region of spacetime that is "shaped" (not quite the right word, but it'll do) so that there are no paths leading back across the event horizon. Thus it doesn't matter if incoming particles interact with other matter or not (edit: and GR doesn't have matter anywhere inside the hole anyway) - once they are in there is no route out.
Thanks
 
  • #10
PeroK
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Right, I was thinking about the digging a hole through a uniform sphere planet's axis and doping a ball through it, it comes out the other side the same force it enters in with, that couldn't work with black holes though as it breaks the light limit.
A black hole is vacuum, so I don't think you could dig through one!
 
  • #11
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A black hole is vacuum, so I don't think you could dig through one!
This was a thought experiment I've read in a book once, nothing to do with black holes here.
 
  • #12
Ibix
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This was a thought experiment I've read in a book once, nothing to do with black holes here.
That does indeed work for massive objects made of normal matter, and we'd expect dark matter to pass through without being slowed. You are correct that it doesn't work with black holes, but this is nothing to do with the speed of light limit. It's to do with the geometry of spacetime being such that you simply cannot describe a particle leaving the event horizon.
 
  • #13
sophiecentaur
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Personally, I find DM to be more than very weakly interesting. :oldlaugh:
It's a bit like fairies at the bottom of the garden, for me. Until there's some serious, unequivocal evidence I'm not very interested in 'photoshopped' images of little girls in fairy costumes.
 
  • #14
PAllen
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It's a bit like fairies at the bottom of the garden, for me. Until there's some serious, unequivocal evidence I'm not very interested in 'photoshopped' images of little girls in fairy costumes.
Gravitational lensing from matter invisible at all EM frequencies doesn’t count as evidence for you?

Note, for comparison, no one has or ever will directly measure a quark (unless QCD is fundamentally wrong). We accept accumulated indirect evidence for quarks.
 
  • #15
sophiecentaur
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Gravitational lensing from matter invisible at all EM frequencies doesn’t count as evidence for you?

Note, for comparison, no one has or ever will directly measure a quark (unless QCD is fundamentally wrong). We accept accumulated indirect evidence for quarks.
Something is there and it does quack like a duck. For the time being, we call it a duck but it's all pretty elusive. I think the 'measurable rules' that are followed in elementary particle physics are very consistent and give a bit more (?) firm indirect evidence for Quarks.
 

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