Fifteen repeating extragalactic signals deepen the mystery of fast radio bursts
Fast Radio Bursts (FRB) have puzzled astronomers ever since they were first detected about 10 years ago. Coming in from all corners of space, these strong but extremely short-lived signals can't be explained by any known celestial object, and now the mystery has deepened even further. Normally, FRBs fire off once and aren't heard from again, but one outlier has been particularly chatty over the years. That repeating FRB has kicked into hyperdrive this week, pulsing an unprecedented 15 times in the space of a few hours.
There are plenty of theories about what FRBs could be. The signals are similar to those given off by pulsars and magnetars – rapidly-rotating neutron stars surrounded by powerful magnetic fields – but the problem there is that these signals pulse repeatedly, while the majority of FRBs are a one-and-done deal. Of course, as with any astronomical anomaly, aliens have been trotted out as an explanation, with Harvard astronomers suggesting that we could be picking up noise from radio-powered propulsion systems for spacecraft.
Another idea was that these high-energy pulses were thrown off by cataclysmic events like supernovae, but a signal named FRB 121102 took the air out of that theory when it was found to buck the trend of being a one-hit wonder. Over the years it's released more than 150 bursts, and its origin has been traced to a dwarf galaxy some three billion light-years from Earth.
Over the past week, FRB 121102 has flared up to a level of activity that's never been seen before. Early on the morning of August 26, 15 new pulses were detected by researchers at Breakthrough Listen, an initiative that's monitoring for signals of possible intelligent extraterrestrial origin. Over five hours, the instrument gathered 400 TB of data, scanning a frequency band of between 4 and 8 GHz. Measuring that big a bandwidth should help astronomers more accurately pinpoint how far the signals have traveled and develop a better understanding of what might be causing them.
"The extraordinary capabilities of the backend receiver, which is able to record several gigahertz of bandwidth at a time, split into billions of individual channels, enable a new view of the frequency spectrum of FRBs, and should shed additional light on the processes giving rise to FRB emission," says Vishal Gajjar, a researcher on the Breakthrough Listen project.
Analyzing the data, the team spotted the 15 spikes, with one reaching a frequency as high as 7 GHz, much higher than previous FRBs. The signals were so strong that the Breakthrough Listen team sent out an astronomer's telegram urging the scientific community to check it out, saying "these observations may indicate FRB 121102 is currently in a heightened activity state, and follow-on observations are encouraged."
In the unlikely event that it is aliens, we still shouldn't hold out hope of communicating with them: given the enormous distance involved, these signals left their source some three billion years ago, so they probably stopped waiting for a reply long before our ancestors crawled out of the oceans. Still, there's plenty to learn from the discovery.
"As well as confirming that the source is in a newly active state, the high resolution of the data obtained by the Listen instrument will allow measurement of the properties of these mysterious bursts at a higher precision than ever possible before," says Gajjar.
Source: UC Berkeley