Astronomers at MIT and universities across Canada and the United States have detected a strange, persistent radio signal from a distant galaxy that appears to flash with surprising regularity.
The signal is classified as a fast radio burst, or FRB – an extremely powerful burst of radio waves of unknown astrophysical origin, typically lasting for a few milliseconds at most. However, this new signal lasts up to three seconds, about 1,000 times longer than the average FRB. Within this window, the team detected bursts of radio waves that repeat every 0.2 seconds with a distinct periodic pattern, similar to a heartbeat.
The researchers named the signal FRB 20191221A, and it is currently the longest-lived FRB, with the clearest periodic pattern discovered to date.
The source of the signal is located in a distant galaxy, several billion light years from Earth. What exactly this source could be remains a mystery, although astronomers suspect the signal could be emitted by a radio pulsar or magnetar, both of which are types of neutron stars — the very dense, fast-spinning cores of giant stars.
“There aren’t many things in the universe that emit strictly periodic signals,” says Danielle Micheli, a postdoctoral researcher at MIT’s Kavli Institute for Astrophysics and Space Research. “An example we know of in our galaxy are radio and magnetic pulsars, which rotate and produce a beacon-like beam. We think this new signal could be a magnetar or a pulsar on doping.”
The team hopes to discover more periodic signals from this source, which can then be used as an astrophysical clock. For example, the frequency of the bursts and how they change as the source moves away from Earth can be used to measure the expansion rate of the universe.
This discovery was reported today in the journal temper natureand was authored by members of the CHIME/FRB Collaboration, including MIT co-authors Calvin Leung, Juan Mina-Barra, Caitlin Shen, and Kiyoshi Masui at MIT, along with Micheli, who first led the discovery as a researcher. at McGill University, then as a postdoc at the Massachusetts Institute of Technology.
“Boom, boom, boom”
Since the first FRB discovery in 2007, hundreds of similar radio flashes have been detected across the universe, most recently by the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, an interferometric radio telescope consisting of four large parabolic reflectors located in the Dominion. Radio Astrophysics Observatory in British Columbia, Canada.
CHIME constantly monitors the sky as the Earth rotates, and is designed to pick up radio waves emitted by hydrogen in the very early stages of the universe. The telescope also happens to be sensitive to fast radio bursts, and since it began observing the sky in 2018, CHIME has detected hundreds of FRBs emanating from different parts of the sky.
The vast majority of FRBs observed so far are one-off – ultra-bright bursts of radio waves that last for a few milliseconds before flashing. Researchers recently discovered the first periodic FRB that appears to emit a regular pattern of radio waves. This signal consists of a four-day window of random bursts that then repeat every 16 days. This 16-day cycle indicated a cyclic pattern of activity, although the actual RF signal was random rather than cyclical.
in December. On September 21, 2019, CHIME picked up a signal from a possible FRB, which immediately caught the attention of Michilli, who was scanning the incoming data.
“It was unusual,” he recalls. “It wasn’t very long, lasted about three seconds, but there were periodic peaks that were remarkably accurate, emitting every millisecond—boom, boom, boom—like a heartbeat. This is the first time the signal itself has been periodic.”
In analyzing the radio burst pattern of FRB 20191221A, Mitchell and colleagues found similarities with emissions from radio and magnetic pulsars in our galaxy. Radio pulsars are neutron stars that emit beams of radio waves, appearing to pulsate as the star rotates, while magnetars produce similar emission due to their intense magnetic fields.
The main difference between the new signal and radio emissions from pulsars and magnetospheres in the galaxy is that FRB 20191221A appears to be a million times brighter. The bright flashes may originate from a distant radio pulsar or magnetar that is usually less bright as it rotates and for some unknown reason unleashed a train of bright explosions, in a rare three-second window that CHIME was fortunately positioned to capture, Micheli says.
“CHIME has now discovered many FRBs with different properties,” says Micheli. “We have seen some live inside very turbulent clouds, while others appear to be in clean environments. From the characteristics of this new signal, we can say that around this source, there is a cloud of plasma that must be very turbulent.”
Astronomers hope to catch additional bursts of periodic FRB 20191221A, which could help improve their understanding of their source, and neutron stars in general.
“This discovery raises the question of what could be causing this extreme signal that we haven’t seen before, and how we can use this signal to study the universe,” says Micheli. “Future telescopes promise to detect thousands of FRBs per month, at which point we may find more of these periodic signals.”
This research was supported, in part, by the Canada Foundation for Innovation.