Fast Radio Bursts (FRBs) are millisecond-long strong emissions of radio waves from the depths of space. A complete understanding of their source is lacking. This latest observation adds to the peculiar menagerie of signals we have seen so far, in quite a unique way.
As reported in the journal Nature, FRB 20191221A is so far an incredible find for two reasons. First, it lasts for about three seconds, roughly 1,000 times longer than other FRBs. And second, within the signal, there is a pulsation. Every 0.2 seconds there is a beat within the burst, which the team likens to a cosmic heartbeat.
“It was unusual,” corresponding author Daniele Michilli, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research, said in a statement. “Not only was it very long, lasting about three seconds, but there were periodic peaks that were remarkably precise, emitting every fraction of a second – boom, boom, boom – like a heartbeat. This is the first time the signal itself is periodic.”
So, what is generating this FRB? Astronomers are unsure but the main suspect is the same as most of the other FRBs: a magnetar, a type of neutron star with an incredible magnetic field. These have likely been behind other objects known to repeat their very short pulses and might be behind this one as well.
“There are not many things in the universe that emit strictly periodic signals,” explained Michilli. “Examples that we know of in our own galaxy are radio pulsars and magnetars, which rotate and produce a beamed emission similar to a lighthouse. And we think this new signal could be a magnetar or pulsar on steroids.”
While magnetars fit the bill on several important aspects, the emission of these FRBs is not exactly clear in every scenario. The CHIME observatory that spotted this new FRB has discovered many more and they are hardly made from the same mold.
“CHIME has now detected many FRBs with different properties,” Michilli said. “We’ve seen some that live inside clouds that are very turbulent, while others look like they’re in clean environments. From the properties of this new signal, we can say that around this source, there’s a cloud of plasma that must be extremely turbulent.”
The best hope to better understand FRB 20191221A is either seeing it again or spotting similar events with complex signals within the main FRB.
“This detection raises the question of what could cause this extreme signal that we’ve never seen before, and how can we use this signal to study the universe,” Michilli said. “Future telescopes promise to discover thousands of FRBs a month, and at that point we may find many more of these periodic signals.”