# Dark matter distribution around black holes.

1. Jun 1, 2014

### majormuss

For my research on astrophysics for the summer, a professor gave me this assignment but I don't know where to start. The question is: What methods could be used to find the dark matter distribution around a galaxy's central black hole?

2. Jun 2, 2014

### rexregisanimi

Perhaps start by researching how one determines dark matter distribution around a galaxy and extrapolate downward :)

3. Jun 2, 2014

### enorbet

I'm thinking the question may be designed to determine your (and our) understanding of the nature of Dark Matter and it's interactions. Ask yourself if we know if Black Holes make any or any substantial difference to Dark Matter and it's distribution. In fact, what does seem to affect it's distribution? Is there any relationship from which to extrapolate?

4. Jun 14, 2014

### EdgePenguin

That's not a good idea. If you do that for, say, an NFW halo you get towards infinite density at the centre.

If you are referring to the black hole at the centre of our galaxy, there are stars that can be used as tracers of potential and thus could get you a dark matter distribution. However, there is a slight snag to doing that, which I will leave you to figure out :-)

5. Jun 14, 2014

### rexregisanimi

I was referring to examining stellar motion in the central parts of the galaxy. Examining the motion of stars in orbit around the central black hole and noting deviations, etc. should provide a start in getting the needed information...

Do the NFW equations diverge when integrated from r=0 to some positive value? It's something like 1/r^3, correct? Shouldn't that converge? ...It has been a while for me :)

6. Jun 14, 2014

### EdgePenguin

Yes you do get finite masses integrating the NFW halo from r=0 due to the r^2 factor in the integral element. It's still not a good idea to use it near the central black hole.

Cosmological density profiles like NFW or Einasto (which is popular in N body simulations these days) are based on large scale structure and the region immediately around the black hole is not even slightly resolved.