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since the only thing we know about dark matter that it "attracts" and affect our Baryonic matter's momentum and speed, which means that it does have mass of a sort.

so why didn't we witness a darkmatter-darkmatter interactions in form of collisions of celestial bodies like stars, Black holes or other distinct things, what do we know about that?

PS: it would be very helpful for me if someone has an answer can cite it with a paper on the topic. thanks in advance!

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marked as duplicate by Qmechanic Apr 8 at 6:36

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The standard answer is that dark matter does not seem to interact strongly with itself (although self-interacting dark matter is an active research topic), and does not emit electromagnetic radiation. The latter property means that a clump of dark matter cannot lose energy by radiating it away, and will remain a diffuse clump. Ordinary matter can coalesce, heat up, radiate away the energy, and coalesce further. Hence dark matter seems to form diffuse halos that do not form celestial bodies.

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  • $\begingroup$ "dark matter does not seem to interact strongly with itself " How do we know that? $\endgroup$ – SRS Apr 10 at 18:46
  • $\begingroup$ @SRS - It is partially an inference from the observed halo shapes, partially a prediction from most DM models like WIMPs. It is not entirely ruled out since there could be a strongly interacting fraction that is small compared to the less strongly fraction, but it would complicate the theory for little gain. Still, if you search for interacting dark matter you will find many papers. $\endgroup$ – Anders Sandberg Apr 10 at 19:20

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