From Dr. Becky.

Why doesn’t dark matter collapse? Think about it, gravity pulls on it. There’s a huge amount of it; outweighing all the normal matter in the Universe. So why doesn’t it form dark stars? Dark black holes? Or entire dark galaxies? Instead, it just sits there… in enormous, fuzzy clouds around galaxies.
And that’s weird. Because normal matter doesn’t stay fuzzy, it collapses under its own gravity. It makes planets. It makes stars. It makes black holes. And it was after my last video about whether the Milky Way’s centre could be a dark matter cloud instead of a supermassive black hole, many of you asked: "if the dark matter cloud has the same mass, why doesn’t it just collapse?" So let’s unpack:
1) Why normal matter collapses under gravity in the first place, and
2) The crucial reason why dark matter can’t
because if it could the Universe would look very different!

👩🏽‍💻 I’m Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about black holes, cosmology, dark matter, the early universe, the James Webb Space Telescope, and the biggest unsolved mysteries in astrophysics. I like to focus on how we know things, not just what we know. And especially, the things we still don’t know. If you’ve ever wondered about something in space and couldn’t find an answer online – you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars.