Our old friend FRB 121102 is back, and just in time. Earlier this year, astronomers identified a distinct 157-day cycle in the activity of 121102 FRB, one of many so-called “rapid radio bursts” from deep space. The mysterious signal is turned on again, potentially confirming the previous findings of the University of Manchester. If the cycle continues, there is hope that we can finally know what FRBs are in the not too distant future.
Fast radio bursts are invisible to the human eye, and each pulse lasts only a few milliseconds. However, they release enough energy in a fraction of a second to blow out entire galaxies. Scientists discovered the first FRB in 2001, but no one came in to analyze the data until 2007. Since then, we have seen dozens of these signals, although they were initially randomized. 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 is awakened again and the whole cycle starts again. The recurring nature of FRB 121102 allowed astronomers to trace the source to a dwarf 3 billion light-years away, allowing teams around the world to follow that part of the sky as the reactivation date approached. It was predicted that would happen between July 9 and October 14.
The latest research comes from a team led by Pei Wang at the National Astronomy Observatory of China. There, scientists used the Five Hundred Meters Spherical Radio Telescope (FAST) to spot the first new torches of FRB 121102 on 14 August. The team discovered 12 bursts just in the first day, and unmistakably showed that FRB 121102 is in an active phase again.
China five hundred meters aperture spherical radio telescope.
The new active phase of FRB 121102 strongly supports the established periodicity, but it is not yet certain. Wang reports that he expects FRB 121102 to be quiet again between August 31st and September 9th. Should the FRB remain active thereafter, it may mean that the cycle is not as reliable as we believed or that the source of the FRB has changed in some way.
We do not yet know what causes FRBs, but each new observation of FRB 121102 (and other recurring bursts) brings us closer to the answer. Currently, a kind of neutron star known as magnetar is the leading candidate. These objects have magnetic fields trillion times more intense than the Earth, and some can direct pulsar-like beams of energy.
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