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Astronomers have for the first time observed the ultraviolet echo of X-ray flares from a supermassive black hole in a distant galaxy.
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At the centers of many galaxies lurk supermassive black holes. From time to time they 'scream' — unleashing powerful X-ray flares. Scientists have long puzzled over the nature of these 'quasi-periodic eruptions'. But only now, by observing the source Ansky, have they for the first time caught an ultraviolet echo: a day after the X-ray peak, gas clouds around the black hole lit up in ultraviolet light.
It's like thunder and lightning: the X-ray strike is instantaneous, and the ultraviolet afterglow follows after a delay, like sound after the flash. Only here, the role of the atmosphere is played by gas clouds, which are heated by the X-rays and re-emit light.
The most surprising part is the full day delay. You'd think a flare from a black hole would be instantaneous. But the echo comes leisurely, like sound bouncing off distant walls. This gives scientists a clue to how matter spirals into a black hole, heating its surroundings.
The light from Ansky traveled almost 10 billion years to reach us. We see this black hole as it was when the Universe was three times younger than it is today.