New clues have been uncovered in the mystery of fast radio bursts (FRBs) from space. One of these strange signals has been repeating seemingly at random – but with years of observation, an international study has now found a pattern hidden in the noise, which could help reveal what causes them.
FRBs are hugely energetic pulses of radio that last mere milliseconds. Many of them are one-off events, gone in a flash never to be heard from again, while others repeat at random intervals. Or so we thought.
As the first repeater to be found, FRB 121102 is arguably the most famous FRB. Sometimes it whips into a frenzy, firing off dozens of bursts within hours of each other, while other times we won’t hear a peep out of it for months.
Astronomers have been watching it closely since its discovery in 2012, and with that much data, an international team has now found that its activity isn’t random after all. It follows a very regular pattern.
The team studied 32 bursts detected during a four-year observation run, as well as data from previous studies of the object. They found that all of FRB 121102’s emissions occur within a window of about 90 days, before it falls silent for 67 days. Then, the entire 157-day cycle begins again.
“This exciting discovery highlights how little we know about the origin of FRBs,” says Duncan Lorimer an author of the study. “Further observations of a larger number of FRBs will be needed in order to obtain a clearer picture about these periodic sources and elucidate their origin.”
This is only the second FRB found to have a repeating pattern. Earlier this year astronomers discovered a signal called FRB 180916, which repeated like clockwork on a 16-day cycle, flaring up regularly for about four days before falling silent for the next 12.
Obviously that’s a much quicker cycle, which raises new questions about what actually causes FRBs. A periodic nature, the team says, might link the phenomenon to orbital motions of objects such as stars, neutron stars and black holes. That's backed up by the fact that signals from FRB 121102 are extremely twisted and polarized, which could be caused by a massive black hole nearby.
While FRBs remain a mystery for now, every new piece of the puzzle that astronomers discover brings us closer to an answer.
The research was published in the journal Monthly Notices of the Royal Astronomical Society.
Source: University of Manchester