Astronomers discover a radio “heartbeat” billions of light-years from Earth | MIT News

Astronomers at MIT and universities across Canada and the United States have spotted a strange and persistent radio signal from a distant galaxy that appears to be blinking 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 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 repeating every 0.2 seconds in a clear periodic pattern, similar to a beating heart.

Researchers have labeled signal FRB 20191221A, and it is currently the longest-lived FRB with the clearest periodic pattern yet discovered.

The source of the signal is in a distant galaxy, several billion light-years from Earth. Exactly what that source might be remains a mystery, although astronomers suspect the signal could be coming from either a radio pulsar or a magnetar, both of which are types of neutron stars — extremely dense, fast-spinning, collapsed cores of giant stars.

“There aren’t many things in the universe that emit strictly periodic signals,” says Daniele Michilli, a postdoc at MIT’s Kavli Institute for Astrophysics and Space Research. “Examples that we know of in our own galaxy are radio pulsars and magnetars that rotate and produce a radial emission similar to a lighthouse. And we think this new signal could be a magnetar or a pulsar on steroids.”

The team hopes to discover more periodic signals from this source, which could then be used as an astrophysical clock. For example, the frequency of the explosions and how they change as the source moves away from Earth could be used to measure the rate at which the universe is expanding.

The discovery is reported in the Journal today Natureand was authored by members of the CHIME/FRB collaboration, including MIT co-authors Calvin Leung, Juan Mena-Parra, Kaitlyn Shin, and Kiyoshi Masui of MIT, along with Michilli, who first led the discovery as a researcher at McGill University, and then as a postdoc at MIT.

“boom boom boom”

Since the discovery of the first FRB in 2007, hundreds of similar radio bursts have been detected across the universe, most recently by the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, an interferometric radio telescope made up of four large parabolic reflectors and located at the Dominion Radio Astrophysical Observatory in British Columbia, Canada.

CHIME continuously monitors the sky as the earth rotates and is designed to record 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 spotted hundreds of FRBs emanating from different parts of the sky.

The vast majority of FRBs observed so far are one-off events — ultra-bright bursts of radio waves lasting a few milliseconds before dying out. Researchers recently discovered that first periodic FRB which seemed to emit a regular pattern of radio waves. This signal consisted of a four-day window of random bursts that then repeated every 16 days. This 16-day cycle showed a periodic pattern of activity, although the actual radio burst signal was random rather than periodic.

On December 21, 2019, CHIME picked up a signal from a potential FRB, which immediately caught the attention of Michilli, who was scanning the incoming data.

“It was unusual,” he recalls. “Not only was it very long, lasting about three seconds, but there were periodic spikes that were remarkably precise, sending out every split second — boom, boom, boom — like a heartbeat. This is the first time that the signal itself is periodic.”

Brilliant explosions

Analyzing the pattern of radio bursts from FRB 20191221A, Michilli and his colleagues found similarities to emissions from radio pulsars and magnetars in our own galaxy. Radio pulsars are neutron stars that emit beams of radio waves that appear to pulse as the star rotates, while similar emission is produced by magnetars due to their extreme magnetic fields.

The key difference between the new signal and radio emissions from our own galactic pulsars and magnetars is that FRB 20191221A appears to be more than a million times brighter. Michilli says the glowing flashes may have come from a distant radio pulsar or magnetar, which is usually less bright when spinning, and for some unknown reason has been emitting a train of brilliant outbursts in a rare three-second window that CHIME thankfully does was positioned to be captured.

“CHIME has now discovered many FRBs with different properties,” says Michilli. “We’ve seen some living in very turbulent clouds, while others look like they’re in a clean environment. Based on the properties of this new signal, we can say that there is a plasma plume around this source, which must be extremely turbulent.”

The astronomers hope to detect additional outbursts from the periodic FRB 20191221A that may help refine their understanding of its source and of neutron stars in general.

“This discovery raises the question of what could be causing this extreme signal that we have never seen before and how we can use this signal to study the universe,” says Michilli. “Future telescopes promise to discover thousands of FRBs each month, and at that point we may find many more of these periodic signals.”

This research was supported in part by the Canada Foundation for Innovation.

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