Explained: Mystery Behind Longest-Lasting 'Heartbeat' Radio Signal From Distant Galaxy

A team of scientists from the Massachusetts Institute of Technology (MIT) and other institutions across US and Canada have detected a strange and persistent radio signal from a far-off galaxy that appears to be flashing with surprising regularity.

The source of the signal lies in a distant galaxy, several billion light-years from Earth.

However, the mystery behind exactly what that source of might be remains a mystery, though astronomers suspect the signal could emanate from either a radio pulsar or a magnetar, both of which are types of neutron stars - extremely dense, rapidly spinning collapsed cores of giant stars.

The discovery is publised in the journal Nature, and is authored by members of the CHIME (Canadian Hydrogen Intensity Mapping Experiment Collaboration) FRB, including MIT co-authors Calvin Leung, Juan Mena-Parra, Kaitlyn Shin, and Kiyoshi Masui at MIT, along with Michilli, who led the discovery first as a researcher at McGill University, and then as a postdoc at MIT.

FRB with a periodic pattern like heartbeat

The signal is classified as a fast radio burst, or FRB - an intensely strong burst of radio waves of unknown astrophysical origin, that typically lasts for a few milliseconds at most.

The first FRB was discovered in 2007, and since then, hundreds of these quick, cosmic flashes have been detected coming from various, distant points across the universe.

Many FRBs release super bright radio waves lasting only a few milliseconds at most before disappearing completely, and about 10% of them have been known to repeat and have patterns.

Fast radio bursts are so quick and unexpected that they're difficult to observe. One resource used to spot them is a radio telescope called the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, at the Dominion Radio Astrophysical Observatory in British Columbia, Canada.

However, the new signal persists for 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 in a clear periodic pattern, similar to a beating heart.

The researchers have labeled the signal FRB 20191221A, and it is currently the longest-lasting FRB, with the clearest periodic pattern, detected to date.

Magnetar or Pulsar on steroids

“There are not many things in the universe that emit strictly periodic signals,” says Daniele Michilli, a postdoctoral scholar in MIT’s Kavli Institute for Astrophysics and Space Research.

“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," Michilli said.

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

Discovery of the signal

On 21 December 2019, CHIME, which continuously observes the sky as the Earth rotates, and is designed to pick up radio waves emitted by hydrogen in the very earliest stages of the universe, detected a signal of a potential FRB, which immediately drew the attention of Michilli, who was was scanning the incoming data.

“It was unusual,” Michilli recalls. “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," he said.

Million times brighter

In analyzing the pattern of FRB 20191221A’s radio bursts, Michilli and his colleagues found similarities with emissions from radio pulsars and magnetars in our own galaxy.

Radio pulsars are neutron stars that emit beams of radio waves, appearing to pulse as the star rotates, while a similar emission is produced by magnetars due to their extreme magnetic fields.

The main 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 luminous flashes may originate from a distant radio pulsar or magnetar that is normally less bright as it rotates and for some unknown reason ejected a train of brilliant bursts, in a rare three-second window that CHIME was luckily positioned to catch.

“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," he added.

Signal could help in study of the Universe

The astronomers hope to catch additional bursts from the periodic FRB 20191221A, which can help to refine their understanding of its source, and of neutron stars in general.

“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," he added.