Cosmic radio signals are beamed towards Earth every day - and astronomers have no idea where they originate. Now, a new study finds that these signals, known as fast radio bursts (FRBs), may be caused by "starquakes." The name of this phenomenon tells you everything you need to know - these signals are bright bursts of radio waves that disappear very quickly.
Since their first discovery in 2007, FRBs have been detected thousands of times, some as one-off events and others that recur over predictable or random time frames.
What exactly causes these events to occur remains a mystery, but with so many FRBs now documented, astronomers have been able to make some educated guesses. Some of these have been traced to neutron stars - the collapsed cores of massive stars - particularly those with extremely strong magnetic fields, known as magnetars. Even so, it's still hard to explain how these objects produce the signal.
But now we may be closer to an answer. Scientists at the University of Tokyo analyzed the time-energy correlations of thousands of FRBs from repeating sources and compared them with other high-energy events. Solar flares have been a strong explanation, but interestingly, the team found clear differences between these flares and FRBs. However, there are striking similarities between FRBs and earthquakes.
"First, the probability of an aftershock from a single event is 10%-50%," said Professor Tomonori Totani, co-author of the study. "Second, the aftershock occurrence rate decreases over time as a power of time; third, the aftershock occurrence rate remains constant even when FRB-seismicity (average occurrence rate) changes significantly; and fourth, there is no correlation between the energies of mainshocks and aftershocks."
So, what does this all mean for those of us not well-versed in statistical analysis? The findings suggest that FRBs may not be produced by flares from neutron stars, but by "starquakes," which suddenly release huge amounts of energy, the team said. Even stranger, some neutron stars may actually have solid shells for these quakes to occur—a hypothesis supported by recent X-ray observations of magnetars.
Of course, this strange hypothesis requires more research to confirm or rule out. With so many FRBs occurring regularly, there is no shortage of data to study.
The research was published in the journal Monthly Notices of the Royal Astronomical Society.