There is some evidence that dark matter is self-interacting: https://arstechnica.com/science/2015/04/new-evidence-that-dark-matter-could-be-self-interacting/ ht

There is some evidence that dark matter is self-interacting: https://arstechnica.com/science/2015/04/new-evidence-that-dark-matter-could-be-self-interacting/ https://arstechnica.com/science/2015/04/new-evidence-that-da...