A blaze of X-rays from the center of our galaxy is the burp following a gargantuan (and rather messy) cosmic feast, astronomers reported in February: A massive black hole there devoured something the size of the planet Mercury, and in the process, let loose an outburst so intense that we still see the echoes six decades later.
When matter falls into a black hole, it grows hot and glows brilliantly before vanishing into oblivion. These days the Milky Way’s central black hole, called Sagittarius A*, seems fairly placid. But over the past five years, NASA’s orbiting Chandra X-ray Observatory has monitored “light echoes”—X-rays bouncing off nearby molecular clouds and reflecting back toward Earth—showing that Sagittarius A* had a planet-size banquet not so long ago. “It was about one thousand times brighter than anything we’ve seen from this black hole,” says Caltech astronomer Michael Muno, who led the project. “It’s possible that it could have been a larger mass that fell in.”
Based on the distance of the molecular clouds from Sagittarius A*, astronomers calculate that the original X-ray that burst from the black hole’s lunch must have lit up Earth’s skies 60 years ago—but astronomers did not have the necessary X-ray telescopes back then. Chandra has detected similar, far smaller black-hole snacks since 2000.
When the black hole starts its next planet-size meal, though, the light show will be hard to miss: Muno estimates the X-rays will be 100,000 times brighter than anything seen before. “It would be a spectacular thing to look at,” he says.
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