Cosmic 'Heartbeat' Radio Signal May Have Been a Neutron Star Flash

Astronomers have detected a radio signal from deep space that repeated in a pattern so regular that it's been described as "like a heartbeat"—and they're not sure what caused it.

The signal, known as a fast radio burst (FRB), was detected by researchers using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope in December 2019.

First discovered in 2007, FRBs are a relatively new phenomenon. As their name suggests, FRBs are intense radio emissions that typically last for just a fraction of a second, flaring up in some deep part of the cosmos before blinking out of sight again.

Today we know of multiple FRB signals that have occurred, and it's even thought that several hundred of them occur every single day—but we still don't know for sure what causes them, so it's an active area of astrophysics.

Radio telescopes
A stock photo shows the Very Large Array radio observatory in New Mexico. Astronomers have detected a number of fast radio burst signals over the past several years, and their sources are still uncertain—though neutron stars are suspected. Greg Meland/Getty

In a new study published in the journal Nature on Wednesday, the CHIME scientists say the 2019 signal they detected, called FRB 20191221A, represents one of the most unique FRBs ever spotted, in that it lasted for three whole seconds—1,000 times longer than average. It's been called the longest-duration FRB detected to date.

Another interesting characteristic of FRB 20191221A is that within its three-second duration, the researchers noted a rhythmic pulse that repeated roughly every 0.2 seconds.

"It was unusual," said Daniele Michilli, a researcher at the Massachusetts Institute of Technology (MIT) Kavli Institute for Astrophysics and Space Research who was involved in the study, in a press release. "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."

Mysterious radio signals from outer space may bring to mind alien civilizations since radio astronomers have been hunting for artificial signals for years. However, it's thought that at least some FRBs are caused by magnetars—highly magnetic and rapidly-spinning neutron stars that shoot off beams of radiation into deep space.

Neutron stars are the collapsed cores of much larger stars that are incredibly dense, packing more mass than the sun into a diameter of around 12 miles or so. The CHIME astronomers reckon that FRB 20191221A likely came from a neutron star.

"Such short periodicity provides strong evidence for a neutron-star origin of the event," the study read. "The periodic structures in the bursts could be explained by a rotating neutron star with beamed emission similar to Galactic radio pulsars in which, for an unknown reason, a train of single pulses has an abnormally high luminosity for a short period of time."

They also speculate it could have come from two neutron stars merging together.

Still, some aspects of the radio blast are uncertain. The astronomers are not sure, for instance, where the signal came from or how far it traveled—though it probably came from another galaxy.

The next step will be to see if the source of the FRB can be narrowed down with future observations. A better understanding of FRBs can help us better understand neutron stars.

"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.