Radio burst detected in dwarf galaxy

According to new research, the cosmic object is distinctive compared to other radio burst detections from recent years.

Fast radio bursts, or FRBs, are bursts of radio waves in the space of milliseconds. Individual radio bursts broadcast once and are not repeated.

But repeating high-speed radio bursts are known to emit short, energetic radio waves multiple times.

Astronomers have been able to trace some radio bursts back to their own galaxies, but they have yet to determine the actual cause of the pulses. By learning about the origin of these bright, intense radio emissions, scientists can understand what causes them.

Astronomers discovered the object, called FRB 190520, when it released a burst of radio waves on May 20, 2019. The researchers used the five-hundred-meter Aperture Spherical radio Telescope, or FAST, in China, and discovered the burst in the telescope’s data in November 2019.

When they conducted follow-up observations, the astronomers noticed something unusual: The object gave off frequent, repetitive bursts of radio waves.

In 2020, the team used the Karl G. Jansky Very Large Array, or VLA, telescopes from the National Science Foundation to locate the origin of the burst before zeroing it using the Subaru Telescope in Hawaii.

Subaru’s visible light observations showed that the eruption came from the edge of a distant dwarf galaxy.

A study detailing the findings published Wednesday in the journal Nature.

The VLA observations also revealed that the celestial body continuously emitted weaker radio waves between the repeating bursts. That’s very similar to just one other known repetitive fast radio burst: FRB 121102, discovered in 2016.

The first detection and subsequent tracing of FRB 121102 back to its origin in a small dwarf galaxy more than three billion light-years away was a breakthrough in astronomy. It was the first time astronomers could learn the distance and environment of these mysterious objects.

“Now we really need to explain this twin mystery and why FRBs and persistent radio sources are sometimes found together,” said study co-author Casey Law, a staff scientist in radio astronomy at the California Institute of Technology.

“Is it common when FRBs are young? Or maybe the object making the outbursts is a huge black hole that is sloppily eating a neighboring star? Theorists now have much more detail to work with and space for explanations is narrowing.”

At present, less than five percent of the hundreds of identified fast radio bursts are known to recur, and only a few of them are active on a regular basis.

But FRB 190520 is the only persistently active one, meaning it’s never “turned off” since it was discovered, said study author Di Li, chief scientist for the radio division of the National Astronomical Observatories of China and the FAST Operation Center.

Meanwhile, FRB 121102, “the first known famous repeater, could be disabled for months,” Li said.

The latest findings raise more questions as astronomers now wonder whether there are two types of fast radio bursts.

“Are those that repeat different from those that don’t? What about the ongoing radio emission — is that common?” co-author Kshitij Aggarwal, who was involved in the study as a doctoral student at West Virginia University, said in a statement.

It’s possible that there are different mechanisms causing the radio bursts, or that whatever produces them behaves differently during different stages of evolution.

Previously, scientists have hypothesized that fast radio bursts are caused by the dense remnants left over after a supernova, called a neutron star, or neutron stars with incredibly strong magnetic fields, called magnetars.

FRB 190520 is considered a possible “newborn” object because it was in a dense environment, Law said. That environment could be caused by material released during a supernova, creating a neutron star. Since this material scatters over time, FRB 190520’s bursts may decrease with age.

In the future, Li wants to discover more fast radio bursts.

“A coherent picture of the origin and evolution of FRBs is likely to emerge within a few years,” Li said.

Law is excited about the implications of having a new class of radio wave sources.

“For decades, astronomers thought there were basically two types of radio sources that we could see in other galaxies: accreting supermassive black holes and star-forming activity,” Law said.

“Now we’re saying it can’t be an either/or categorization anymore! There’s a newbie in town and we need to take that into account when studying populations of radio resources in the universe.”