Our old friend FRB 121102 is back, and right on time. Earlier this year, astronomers identified a distinct 157-day cycle in the activity of FRB 121102, one of many so-called “fast radio bursts” emanating from deep space. The mysterious signal has switched back on, potentially confirming the previous findings from the University of Manchester. If the cycle holds, there’s hope we might finally know what FRBs are in the not-too-distant future.
Fast radio bursts are invisible to the human eye, and each pulse only lasts a few milliseconds. However, they release enough energy during that fraction of a second to outshine entire galaxies. Scientists detected the first FRB in 2001, but no one got around to analyzing the data until 2007. Since then, we’ve spotted dozens of these signals, although they seemed random at first. Recently, scientists have identified some FRBs that repeat, but FRB 121102 is the first known to repeat on a regular cycle.
The cycle identified earlier this year predicts a period of activity for 67 days followed by 90 days of silence. Then, FRB 121102 awakens again and starts the whole cycle over again. The repeating nature of FRB 121102 allowed astronomers to track its source to a dwarf galaxy 3 billion light-years away, so teams around the world have been watching that part of the sky as the reactivation date approached. It was predicted that would happen between July 9th and October 14th.
The latest research comes from a team led by Pei Wang at the National Astronomy Observatory of China. There, scientists used the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to spot the first new flares from FRB 121102 on August 14th. The team detected 12 bursts in just the first day, showing undeniably that FRB 121102 is in an active phase once again.
The new active phase of FRB 121102 strongly supports the established periodicity, but it’s not a sure thing yet. Wang reports that he expects FRB 121102 to go silent again between August 31st and September 9th. Should the FRB remain active after that, it could mean the cycle isn’t as reliable as we believed or that the source of the FRB has changed in some way.
We still don’t know what causes FRBs, but every new observation of FRB 121102 (and other repeating bursts) gets us closer to the answer. Currently, a type of neutron star known as a magnetar is the leading candidate. These objects have magnetic fields a trillion times more intense than Earth’s, and some can direct pulsar-like beams of energy.