Photo: "Sleeping" Black Hole Briefly Awoke in 1700s

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Pockets of the gas cloud Sagittarius B2 brightened and faded over nearly 12 years, as observed by four x-ray satellites.

These light echoes (circled above) were caused by x-ray output from the Milky Way's once-active, but now slumbering, supermassive black hole.

Images courtesy ASCA and Suzaku: JAXA; Chandra: NASA/CXC; XMM-Newton: ESA

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