The beacon flares up and then nearly goes out, even though the lamp inside burns steadily. That is exactly what astronomers saw when they pointed their telescopes at the galaxy I Zwicky 1. At its center sits a supermassive black hole that devours gas and dust so greedily that a scorching disk forms around it, shining brighter than an entire galaxy. But the X-rays coming from the very core behave strangely: their brightness jumps by several times within days.
The explanation lies in the "weather" around the black hole. The disk, like an overheated boiler, ejects powerful streams of matter — a stellar wind. However, this wind is not continuous but consists of many individual clumps, like wisps of fog. When such a clump drifts between us and the hot corona (the region above the disk where X-rays are born), it partially blocks the light. We see the signal weaken. When the clump moves away, the brightness recovers. The authors counted three such absorbing clouds with different densities that orchestrate this cosmic spectacle.
This picture turned out to be universal for a whole class of active nuclei — narrow-line Seyfert galaxies of type 1. Their X-ray trembling is most likely always explained by a clumpy wind, not by the whims of the black hole itself. This gives astronomers a new tool: by observing the flickering, they can reconstruct the structure of invisible outflows that carry matter away from the voracious monster.
The black hole in I Zwicky 1 accretes matter so rapidly that the pressure of its own radiation should blow the disk apart. But the disk holds together, and it is precisely this "super-Eddington" regime that produces that clumpy wind.
A similar image of a "flickering" black hole is explored in Vernor Vinge's novel "A Fire Upon the Deep," where the instability of a supermassive object's radiation becomes the key to unraveling an ancient catastrophe.