While black holes themselves swallow any light beyond their event horizon, the area outside the event horizon tends to emit lots of light. That’s because the material falling in toward the black hole is extremely energetic as it sheds angular momentum and crashes in to other material in orbit around the black hole. So, while we can’t image a black hole directly, we can infer some things about its properties using light from the environment it creates.
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This week saw the publication of two papers that edge in to the area close to the event horizon, imaging events in an area that includes some of the closest stable orbits to the black hole. And, in doing so, one of them finds that a supermassive black hole is spinning so fast that a location on its surface would move at roughly half the speed of light.
Echoes of a corona
Both of these papers take advantage of periodic outbursts that happen when the black hole starts to feed on new material. That material heads into the hole via a flat structure centered on the black hole called an accretion disk. Its arrival heats the disk up, causes the black hole to brighten, and causes changes in the local environment. The questions that these two papers focus on is what these changes can tell us about the black hole and the environment nearby.