Mysterious repeat radio flash, 3 billion light-years from Earth

This phenomenon is very different from FRB findings in recent years, according to new research detailed in the journal Nature on June 8.

Radio bursts, or FRBs, are radio waves emitted in 1/1,000th of a second in space. Individual radio bursts usually emit a single wave and do not repeat. However, a repeat FRB will oscillate many times, with radio waves being short and carrying a lot of energy.

Astronomers have been able to track some of the radio bursts in our galaxy, but they have yet to determine the true cause of the pulsations. Learning more about the source of these bright and intense radio emissions can help scientists understand what causes them.

'Never off'

Astronomers discovered the event, dubbed FRB 190520, when they observed a radio burst in 2019. The team used a 500 aperture spherical radio telescope m (or FAST) in China, and detected the explosion in the telescope's November 2019 data. As they continued to observe, astronomers noticed something unusual: FRB 190520 was emitting regular, repeating radio waves.

Image taken with the Karl G. Jansky Very Large Array telescope, showing the active FRB 190520 (red). (Photo: NSF/CFHT).

In 2020, the team used the National Science Foundation's Karl G. Jansky Very Large Array (VLA) telescope to determine the source of the explosion, before using the Subaru telescope in Hawaii. Subaru's observations in visible light suggest that the explosion came from the fringes of a distant dwarf galaxy.

The VLA observations also showed that the explosion continuously emitted radio waves and weakened with each wave.

This phenomenon is very similar to a repeating radio flash observed in 2016 as FRB 121102. It is also thought to have originated in a small dwarf galaxy more than 3 billion light-years away. The discovery was then considered a breakthrough in astronomy, as it was the first time that astronomers were able to learn about the distances and environments of such mysterious events.

Currently, less than 5% of the hundreds of radio bursts are identified as 'repeating' types, and only a few of them are active.

But FRB 190520 is the only one that is persistently active, meaning it has never "turned off" since its discovery, said Di Li, study author and head of the radio division of the National Astronomical Observatory. China and the FAST Operations Center, said.

Meanwhile, FRB 121102, "the first known well-known repeat radio flash may have died out after many months," said Mr. Li.

New questions

The latest discovery raises more questions for scientists. They raised the question of whether there could be two types of FRBs.

'How is a repeating type different from a non-repeating type? Is continuous radio emission a common phenomenon?', said study co-author Kshitij Aggarwal.

Simulation of a magnetic star emitting radio waves (red).

Previously, scientists had hypothesized that FRBs arise from dense remnants left over from supernova explosions. These remnants are neutron stars, or magnetic stars - a type of neutron star with an extremely strong magnetic field.

FRB 190520 has been hypothesized to be a 'newborn' explosion because the matter surrounding it is so dense, said Casey Law, study co-author and radio astronomy scientist at the California Institute of Technology, speak. As this amount of matter disperses over time, the waves from FRB 190520 may decrease.

From the discovery of FRB 190520, Mr. Li hopes to detect more radio bursts in the future. 'A consistent picture of the origin and evolution of FRBs is likely to emerge over the next few years,' he said.