The culprit is a staggering flare-up of Markarian 421, a "blazar" that hosts a supermassive black hole.

BBC: Blazar Markarian 421's flare-up is cosmic coincidence

The name of Markarian 421 is cropping up in many talks at the American Physical Society meeting in Denver.

BBC: Blazar Markarian 421's flare-up is cosmic coincidence

Markarian 421 was already in the known catalogue of blazars, being somewhat variable and having had something of a brightening, or flare, in 1996.

BBC: Blazar Markarian 421's flare-up is cosmic coincidence

First Byurakan Survey (FBS or Markarian survey, Armenia) , containing the records of a unique astronomical survey carried out by the Byurakan Astrophysical Observatory (BAO) from 1965-1980.

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Susie Dowd Markarian, a Santa Rosa, Calif.

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Fermi and a laundry list of the world's great observatories on the ground and in space were all watching because of a coordinated plan to study Markarian 421 across a number of "colours" of light from radio to gamma-ray.

BBC: Blazar Markarian 421's flare-up is cosmic coincidence