Five billion years ago, a great disturbance rocked a region near the monster black hole at the center of the galaxy 3C 279. On June 14, 2015, the pulse of high-energy light produced by this event finally arrived at Earth, setting off Fermi's Large Area Telescope and other observatories. Astronomers around the world turned instruments toward the galaxy to observe this brief but record-setting flare in greater detail.
3C 279 is a famous blazar, a galaxy whose high-energy activity is powered by a central supermassive black hole weighing up to a billion times the Sun's mass and roughly the size of our planetary system. As matter falls toward the black hole, some particles race away at nearly the speed of light along a pair of jets pointed in opposite directions. What makes a blazar so bright is that one of these particle jets happens to be aimed almost straight at us.
The brightest persistent source in the gamma-ray sky is the Vela pulsar, which is about 1,000 light-years away. 3C 279 is millions of times farther off, but during this flare it became four times brighter than Vela, as shown in this gamma-ray image. This corresponds to a tremendous energy release, and one that cannot be sustained for long.
The galaxy rapidly brightened in less than a day, peaked on June 16, 2015, and dimmed to normal gamma-ray levels by three days later. The rapid fading is why astronomers rush to collect data as soon as they detect a blazar flare.