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Of all the mind-bending phenomena in the cosmos, few are more tantalizing than fast radio bursts, or FRBs. Since the first detection in 2007, these mysterious radio signals emanating from the void have puzzled scientists searching for their source. Some of them even repeat, and demonstrate unexplained patterns of activity.
Now, a new look at the first repeater ever discovered—FRB 121102, first observed in 2012—has revealed some amazing insights. An international team of scientists recorded an incredible 1,652 independent radio bursts from the mysterious source in just 47 days, according to a study published in Nature on Wednesday. The finding represents the highest activity ever recorded from an FRB, with 122 radio bursts coming in the span of one hour in one instance.
The scale of the discovery is remarkable: the total number of previously reported FRBs from this source was a mere 349. "This is the largest sample of bursts from one FRB source collected so far," Dr. Bing Zhang, a professor of physics and astronomy at the University of Nevada Las Vegas and study co-author, said in an email.
The observations, made using the Five-hundred-meter Aperture Spherical Telescope (FAST) in China between August 29 and October 29, 2019, have allowed scientists to characterize the radio bursts coming from FRB 121102 like never before. What they discovered complicates the search for a source even as it narrows down the field of possibilities. The vast number of detections allowed the researchers to thoroughly search for any sign of periodicity, or quasi-periodicity, meaning a pattern in the repeating signals that might indicate a single spinning source such as a pulsar. They found none.
"There might be more than one mechanism to generate FRBs from one source, even though observations of more repeating sources are needed to confirm this," Zhang wrote. "Since FRB 121102 is a representative of active repeaters, these implications apply to all repeaters in general."
That being said, Zhang noted that the new research essentially rules out one leading theory for the source of FRBs.
"The leading model to interpret FRBs invokes magnetars, the most magnetized neutron stars in the universe," he wrote. "There are two versions of it, one involving the magnetosphere of the magnetar to emit FRBs, another invoking shocks far from the magnetosphere to generate them. This observation disfavors the latter mechanism which has a very low efficiency to generate bursts. Because there are so many bursts produced in a short time, some of them are only separated by milliseconds, it is essentially impossible for the latter model to work. Our results suggest that the bursts are likely produced from the magnetospheres of magnetars, if magnetars are indeed the sources of repeating FRBs.”
We already know quite a bit about FRB 121102, due to its status as the first repeater FRB ever detected. For example, we know it has an active phase followed by 67 days of inactivity. We also know that it comes from a dwarf galaxy in a star-forming region of space three billion light years away. But as the new study shows, we definitely don't know enough about this mysterious radio source, or others like it, yet.
"My collaboration team is utilising FAST to monitor other repeating FRBs and some unexpected exciting results are being accumulated," Zhang wrote. "Stay tuned!"