Cosmic mystery of fast radio bursts deepens with flurry of activity
A huge new dataset could soon help unlock the cosmic mystery of fast radio bursts (FRBs). In the space of a few weeks, over 1,600 new signals were detected coming from one of the most well-studied sources of FRBs, essentially ruling out a leading hypothesis on their origin.
In true scientific fashion, the name tells you everything you need to know – these signals are millisecond-long bursts of radio waves, each one carrying more energy than the Sun emits in a year. Some of them are one-hit wonders, while others repeat either randomly or on a predictable schedule.
But exactly what creates them remains a mystery. Black holes, supernovae, neutron stars, exotic particles, and of course aliens have all been proposed as explanations, but the leading candidate is magnetars, compact stars with incredibly powerful magnetic fields. The smoking gun, it seemed, was the recent detection of a magnetar in our own galaxy caught firing off suspiciously FRB-like signals.
A new study, however, complicates the picture. Astronomers used the Five-hundred-meter Aperture Spherical Telescope (FAST) in China to closely examine one of the most famous FRB sources. FRB 121102 was the first repeating signal discovered, so it’s been one of the most well-studied over the years. But these new observations reveal that it’s far more active than previously thought.
The team watched the source for almost 60 hours over 47 days in 2019, detecting an astonishing 1,652 bursts. That’s a huge increase – previously, only 347 bursts in total have been recorded from this source since its discovery in 2012. Expanding the dataset so drastically could help unlock the FRB mystery.
“This was the first time that one FRB source was studied in such great detail,” says Bing Zhang, corresponding author of the study. “The large burst set helped our team hone in like never before on the characteristic energy and energy distribution of FRBs, which sheds new light on the engine that powers these mysterious phenomena.”
At its most active, FRB 121102 was detected producing 122 bursts within the space of one hour – the highest repeat rate of any FRB source. The team says that this flurry of activity could help decide between the two main models for how magnetars could produce repeating FRBs. The first hypothesizes that the signals arise from inside the star’s magnetic field, while the second says that they’re produced by recurring “shocks” to material around the star.
“These results pose great challenges to the latter model,” says Zhang. “The bursts are too frequent and - given that this episode alone amounts to 3.8 percent of the energy available from a magnetar - it adds up to too much energy for the second model to work.”
With so many data points in hand, the team also checked for any kind of repeating pattern to the bursts, on scales between one millisecond and 1,000 seconds. None were found, which seems to suggest that no single compact object, such as a magnetar, is responsible.
In a way, that only deepens the mystery. But it doesn’t rule out magnetars as an FRB source completely – there could be two of them orbiting very closely, with the signals arising from their interactions. Even if FRB 121102 isn’t a magnetar, that doesn’t mean the objects aren’t behind other FRBs – after all, different signals have such a wide range of characteristics that multiple explanations could be at play.
The new research was published in the journal Nature.
Source: University of Nevada Las Vegas