Stephanie LaMassa did a double take. She was staring at two images on her computer screen, both of the same object — except they looked nothing alike.

The first image, captured in 2000 with the Sloan Digital Sky Survey, resembled a classic quasar: an extremely bright and distant object powered by a ravenous supermassive black hole in the center of a galaxy. It was blue, with broad peaks of light. But the second image, measured in 2010, was one-tenth its former brightness and did not exhibit those same peaks.

The quasar seemed to have vanished, leaving just another galaxy.

That had to be impossible, she thought. Although quasars turn off, transitioning into mere galaxies, the process should take 10,000 years or more. This quasar appeared to have shut down in less than 10 years — a cosmic eyeblink.

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