Black holes don’t glow – in fact, they’re famous for doing the opposite. But if they’re actively devouring material from the space around them, that material can blaze like a billion X-ray Suns.

And for the first time, astronomers have now seen that blaze mysteriously snuffed out, before gradually returning to brightness.

The supermassive black hole is a beast clocking in at 19 million solar masses, powering a galactic nucleus 275 million light-years away, in a galaxy called 1ES 1927+654.

Over a period of just 40 days, astronomers watched as its corona absolutely plummeted in brightness, before rising again to shine brighter than before.

“We expect that luminosity changes this big should vary on timescales of many thousands to millions of years,” said physicist Erin Kara of the Massachusetts Institute of Technology (MIT).

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“But in this object, we saw it change by [a factor of] 10,000 over a year, and it even changed by a factor of 100 in eight hours, which is just totally unheard of and really mind-boggling.”

There are several components to the area immediately around a black hole. There’s the event horizon; that’s the famous “point of no return”, at which even light speed is not sufficient to attain escape velocity. An active black hole also has an accretion disc, a huge disc of material swirling into the object, like water circling a drain.

Read more: Science Alert