What happens to dark matter in the gravity field of a black hole?
J.C. Chauveau
Le Mesnil-Saint-Denis, France
Dark matter interacts via gravity, so it will orbit a black hole like any other particle — just like everything in the solar system revolves around the Sun. Occasionally, dark matter particles can get knocked onto paths that cause them to fall directly into the black hole. So that black hole is made partially of dark matter.
But most of a black hole’s mass comes from normal matter like electrons and protons falling in, not dark matter. This is because normal matter in orbit around a black hole can feel frictional forces that cause it to fall in rapidly. Dark matter doesn’t interact via the electromagnetic force, and therefore doesn’t experience friction. Hence, most of the time, dark matter particles simply orbit around the black hole rather than falling in.
Eliot Quataert
University of California, Berkeley
