Comment by Aseyhe on 23/09/2021 at 13:41 UTC*

47 upvotes, 1 direct replies (showing 1)

View submission: Why is the dark matter halo spherical?

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One hypothetical example is self-interacting dark matter. In that model, dark matter halos actually become more spherical than halos of non-self-interacting dark matter. This paper[1] has some example pictures (Figure 7).

1: https://academic.oup.com/mnras/article/472/3/2945/4104642

Some background: one major motivator for self-interacting dark matter is that it can produce halos whose central density does not go to infinity. This could potentially match observations better. It is not yet clear that there is actually a discrepancy between non-self-interacting dark matter and observations, though, for two reasons:

• The gravitational influence of the ordinary matter can smooth out the central halo density even without any dark matter collisions.

• The dark matter distribution within halos has to be inferred indirectly by, for example, the motions of stars. The precise dark matter distribution that you infer depends on assumptions about the three-dimensional stellar distribution (which you only observe in the line-of-sight projection). Here's[2] an interesting relatively recent paper on that.

2: https://academic.oup.com/mnras/article/474/1/1398/4590054

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Comment by sticklebat at 24/09/2021 at 00:25 UTC

3 upvotes, 1 direct replies

Some background: one major motivator for self-interacting dark matter is that it can produce halos whose central density does not go to infinity.

I don’t understand this. Why would non-interacting dark matter necessitate an infinite central density? I understand why it would be higher than in an interacting case, but not why it would be infinite.