Most cosmic events happen on huge timescales. Not so for quasars – the bright centres of galaxies that are powered by supermassive black holes gobbling down gas and dust. We have just seen them ignite in a matter of years.
Astronomers expect quasars to use up their fuel and settle down into quiet galaxies – a process that should take hundreds of thousands of years. So last year, when a dozen quasars were spotted shutting down in just hundreds of days, it was a shock.
Chelsea MacLeod of the University of Edinburgh, UK, and her colleagues wondered if these objects might turn on again. The team compared images of galaxies from the Sloan Digital Sky Survey (SDSS) with images of the same objects from the Pan-STARRS survey, taken 10 years later. After flagging 1000 objects that varied in brightness from one survey to the next, the team pinpointed five galaxies that appeared to shape-shift into quasars.
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