DNEWS VIDEO: THE MILKY WAY'S OWN BLACK HOLE.
Furthermore, there is indirect evidence - obtained by measuring the velocity distributions of stars within a given galaxy - that many of the black holes observed thus far appear to be rotating, some as fast as a million miles per hour, thereby giving a black hole angular momentum. And when they rotate, they drag space-time into a vortex, pretty much forcing any objects - including light particles - to follow the same path of rotation.
(Here's an interesting bit of trivia. Technically, a rotating black hole has two event horizons: the outer horizon that marks the point of no return for objects falling into the black hole, and an inner horizon closer to the center, arising from the hole's angular momentum.)
But ideally, physicists would love to be able to measure that rate of rotation directly, in part because that telltale distribution of stars might be influenced by other factors - exotic stuff like dark matter in particular.
That's the gist of a new paper appearing in Nature Physics this week, by a team of physicists who looked at how light behaves in experiments with lasers and lenses.