Powerful bursts of radio waves emanating from a distant dwarf galaxy and detected by a massive telescope in China are bringing scientists closer to solving a so-called “cosmic mystery” that has lingered for years.
Since its discovery in 2007, astronomers have struggled to understand what causes phenomena called fast radio bursts, which involve pulses of radiofrequency electromagnetic radiation originating from places within the Milky Way and other galaxies.
Radio waves have the longest wavelength in the electromagnetic spectrum. Astronomers suspect these outbursts could be triggered by certain extreme objects. These might include: a neutron star, the collapsed compact core of a massive star that exploded as a supernova at the end of its life cycle; a magnetar, a type of neutron star with an ultra-strong magnetic field; and a black hole disorderly eating a neighboring star.
Researchers said Wednesday that they had detected a fast radio burst, or FRB, originating from a dwarf galaxy located about 3 billion light-years from Earth. A light year is the distance light travels in one year — 9.5 trillion kilometers. The collective stellar mass of this galaxy is approximately 1/2500th of our Milky Way.
The FRB was first seen in 2019 through the FAST telescope in the Chinese province of Guizhou, the world’s largest single-dish radio telescope, which has a signal reception area equal to 30 football fields. It was most studied with the VLA telescope in New Mexico (USA).
“We still call fast radio bursts a cosmic mystery, and rightly so,” said astrophysicist Di Li of the Chinese Academy of Sciences in Beijing, FAST’s chief scientist and co-author of the research published in the journal Nature.
“Fast radio bursts are intense, brief flashes of radio light that are powerful enough to be seen from across the universe,” added Caltech astronomer Casey Law, co-author of the study. “The burst flashes in about a millisecond, much faster than the blink of an eye. Some sources of FRBs have been found that emit multiple bursts in what look like storms of activity, but others have only been seen exploding once.”
The just-described FRB is one that repeats itself and also has a persistent but weaker radio emission between bursts. In other words, it always remains “on”. Most of the 500 or so known FRBs do not repeat. The nova looks a lot like another, discovered in 2016, which was the first FRB whose location was identified.
Li noted that numerous hypotheses have been offered to try to explain these explosions.
“The abundance of models reflects our lack of understanding of FRBs. Our work favors active repeaters that are born from an extreme explosive event, such as a supernova. These active repeaters are also young, as they need to be seen shortly after the birth event,” he said. read​
Astronomers suspect that the newly described FRB is a “newborn”, still shrouded in dense material blown into space by a supernova explosion that left behind a neutron star. They said repeated bursts could be a feature of younger FRBs, perhaps dissipating over time.
Findings like the FRB just described could help scientists determine the cause of these radio bursts. Scientists have previously been able to come up with an explanation for the cause of another enigmatic phenomenon — extremely energetic explosions called gamma-ray bursts — as originating from the death of stars, merging neutron stars and magnetars.
“FRBs have quickly grown to become a wonderful example of an astrophysical puzzle, just as gamma-ray bursts were a few decades ago,” Law said. “We know more and more about the phenomenon, where the sources live, how often they explode, etc. However, we are still chasing that gold measurement that will give us a definitive answer to what causes them.”
