At the center of the distant galaxy MCG-6-30-15 lies a supermassive black hole. Around it swirls a disk of incandescent gas, and above the disk hangs a cloud of even hotter particles — the corona. In February 2024, three X-ray telescopes (XRISM, NuSTAR, and XMM-Newton) observed this system simultaneously. They captured light reflected off the disk and used it to track the corona's motions.
The corona behaved like a living thing. Usually it stayed close to the black hole — within ten gravitational radii, where gravity is already intense. But during the flare, it puffed up to fifteen radii and flew away at 0.27 times the speed of light — about 80,000 kilometers per second. After the flare, the corona contracted again, this time to a tiny region of 2.5 radii. These swings altered the reflected light, and the telescopes recorded every change.
These observations matter not just as a pretty picture. From the reflected X-ray light, scientists measure how fast the black hole spins. If you ignore that the corona moved and changed size, you can get the estimate wrong. Now that the corona's motions are recorded, the spin is pinned down more precisely: it turns out to be extremely fast — greater than 0.93 of the maximum possible.
The corona above a black hole is like a boiling lid on a pot of bubbling soup. It lifts and presses down, and by its trembling you can tell what's going on inside.
The speed at which the corona flew away from the black hole is 0.27 times the speed of light. That's about 80,000 kilometers per second: in one second, such a cloud would cross the Atlantic Ocean 16 times.
In the movie Interstellar, the characters approach the supermassive black hole Gargantua and see its accretion disk. Observations of MCG-6-30-15 show that real disks are also surrounded by a hot corona that can be ejected outward.