Jutta Kunz

A top spun to its limit changes the air flow around it — the air swirls differently than around a barely spinning top. Black holes in some extended theories of gravity behave similarly. When a hole spins fast enough, the curved spacetime near its poles acquires new properties.

At the center of almost every large galaxy lurks something supermassive and dark. Most often, that something is thought to be a black hole — a region where gravity is so strong that even light cannot escape. But what if it's not a black hole, but a dense ball of ultralight particles — a boson star?