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!
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.
