By Ashley Strickland, June 10: Astronomers have detected a mysterious, repeating fast radio burst emanating from a dwarf galaxy located 3 billion light-years away.
The cosmic object is distinctive when compared with other detections of radio bursts in recent years, according to new research.
Fast radio bursts, or FRBs, are millisecond-long bursts of radio waves in space. Individual radio bursts emit once and don't repeat. But repeating fast radio bursts are known to send out short, energetic radio waves multiple times.
Astronomers have been able to trace some radio bursts back to their home galaxies, but they have yet to determine the actual cause of the pulses. Learning more about the origin of these bright, intense radio emissions could help scientists understand what causes them.
Astronomers detected the object, named 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 data in November 2019. When they conducted follow-up observations, the astronomers noticed something unusual -- the object was releasing frequent, repeating bursts of radio waves.
In 2020, the team used the National Science Foundation's Karl G. Jansky Very Large Array, or VLA, telescopes to pinpoint the origin of the burst before zeroing in on it using the Subaru Telescope in Hawaii. Subaru's observations in visible light showed that the burst came from the outskirts of a distant dwarf galaxy.
A study detailing the findings was published in the journal Nature.
Two of a kind
The VLA observations also revealed that the celestial object constantly released weaker radio waves between the repeating bursts. That's very similar to only one other known repeating fast radio burst: FRB 121102, discovered in 2016.
The initial detection and subsequent tracing of FRB 121102 back to its origin point in a small dwarf galaxy more than 3 billion light-years away was a breakthrough in astronomy. It was the first time astronomers were able to learn about the distance and environment of these mysterious objects.
"Now we actually need to explain this double mystery and why FRBs and persistent radio sources are found together sometimes," said study coauthor Casey Law, a staff scientist in radio astronomy at the California Institute of Technology. "Is it common when FRBs are young? Or perhaps the object that makes the bursts is a massive black hole that is messily eating up a neighbouring star? Theorists have a lot more detail to work with now and the scope for explanation is shrinking."
Currently, less than 5% of the hundreds of identified fast radio bursts have been known to repeat and only a few of them are regularly active.
But FRB 190520 is the only persistently active one, meaning that it has never "turned off" since being 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, can turn off for months," Li said.
The latest findings raise more questions because now astronomers wonder if there might be two kinds of fast radio bursts.
"Are those that repeat different from those that don't? What about the persistent radio emission -- is that common?" said study coauthor Kshitij Aggarwal, who was involved in the study as a doctoral student at West Virginia University, in a statement.
It's possible that there are different mechanisms that cause the radio bursts, or that whatever produces them is behaving differently during various stages of evolution.
Previously, scientists have hypothesized that fast radio bursts are caused by the dense remnants leftover after a supernova, called a neutron star, or neutron stars with incredibly strong magnetic fields called magnetars.
FRB 190520 is being considered as a possible "newborn" object because it was located in a dense environment, Law said. That environment may be caused by material released by a supernova, which resulted in the creation of a neutron star. As this material scatters over time, the bursts from FRB 190520 may decrease as it ages.
Going forward, Li wants to discover more fast radio bursts.
"A coherent picture of the origin and evolution of FRBs is likely to emerge in just 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 kinds of radio source that we could see in other galaxies: accreting supermassive black holes and star formation activity," Law said. "Now we're saying that it can't be an either/or categorization anymore! There is a new kid in town and we should consider that when studying populations of radio sources in the universe."