Fast Radio Bursts, or FRBs, are intense one-millisecond bursts of radio waves of unknown origin. The first FRB was discovered in 2007, and since then hundreds of these fast cosmic flashes have been detected originating from various distant points across the universe.
Many FRBs emit super bright radio waves that only last a few milliseconds at most before completely fading, and about 10% of them are known to repeat and have patterns.
This telescope, in operation since 2018, constantly observes the sky and, in addition to fast radio bursts, is sensitive to radio waves emitted by distant hydrogen in the universe.
Astronomers using CHIME spotted something on December 21, 2019, that immediately caught their attention: a fast radio burst that was “peculiar in many ways”, according to postdoctoral researcher Daniele Michilli at the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology.
The signal, named FRB 20191221A, lasted up to three seconds, about 1,000 times longer than typical fast radio bursts.
Michilli was monitoring data as it came in from CHIME when the burst happened. The signal is the longest-lasting fast radio burst to date.
“It was unusual,” Michilli said. “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. C is the first time that the signal itself is periodic.”
While FRB 20191221A has yet to repeat, “the signal is formed by a train of consecutive peaks that we found separated by approximately 0.2 seconds,” he said in an email.
An unknown origin
The research team doesn’t know the exact galaxy the burst originated from and even the estimated distance of a billion light-years is “highly uncertain”, Michilli said. While CHIME is primed to search for bursts of radio waves, it is not as good at locating their points of origin.
However, CHIME is being upgraded through a project where additional telescopes, currently under construction, will observe together and be able to triangulate radio bursts to specific galaxies, he said.
But the signal holds clues to where it came from and what may have caused it.
“CHIME has now detected many FRBs with different properties,” Michilli said. “We have seen some living inside very turbulent clouds, while others seem to be in clean environments. From the properties of this new signal, we can say that around this source , there is a plasma cloud that must be extremely turbulent.”
When the researchers analyzed FRB 20191221A, the signal was similar to emissions emitted by two different types of neutron stars, or the dense remnants after the death of a giant star, called radio pulsars and magnetars.
Magnetars are neutron stars with incredibly strong magnetic fields, while radio pulsars emit radio waves that appear to pulse as the neutron star rotates. The two stellar objects create a signal similar to the flashing beam of a lighthouse.
The fast radio burst appears to be more than a million times brighter than these broadcasts. “We think this new signal could be a magnetar or a pulsar on steroids,” Michilli said.
The research team will continue to use CHIME to monitor the sky for more signals from this radio burst, as well as others with a similar periodic signal. The frequency of radio waves and their evolution could be used to help astronomers learn more about the expansion rate of the universe.
“This detection raises the question of what could be causing 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 per month, and by then we might find many more of these periodic signals.”