For 17 straight years, the Fermi space telescope recorded light from the distant galaxy 4C 76.03. Most of the time, it behaved quietly, like a night city with only a few lit windows. But in the observation archive, two brief moments stood out when the galaxy flared in gamma rays — the most energetic light in the universe.
The first flare lasted about a month, the second three weeks. They were separated by two and a half years of calm. The brightness and character of the emission in both flares were nearly identical, as if the same mechanism had fired twice. Astronomers believe that at these moments, new clumps of plasma were born at the galaxy's center — jets shooting out from near the black hole at nearly the speed of light.
The galaxy 4C 76.03 itself is already a few hundred million years old, but its radio structure is small — less than a thousand light-years across. Objects like this are called young radio galaxies. The gamma-ray flares indicate that activity in the core is still ongoing. Perhaps the galaxy is going through a transitional phase: it is no longer an infant, but not yet an adult, and new energy outflows help it grow beyond its typical size.
Gamma rays from this galaxy traveled to Earth for over a billion years, yet the flares lasted only a few weeks, like a brief beacon signal in a dark ocean.