A New Mystery Signal Is Repeating From a Distant Galaxy

The riddle of what is causing these tremendous outbursts has been exacerbated by the discovery of a new source of recurring rapid radio bursts.

The source, which was discovered in 2019 and given the designation FRB 190520B, appears to be firing out millisecond bursts of intense radio waves on a regular basis.

Astronomers have been able to conduct investigations that disclose information about where it originates from in the Universe and the space around it as a result of this. These findings show that there are likely several mechanisms at work in the huge wide universe that might cause these unusual eruptions.

Fast radio bursts (FRBs) are very short bursts of radiation (less than a millisecond in duration) that flash brightly at radio frequencies.

The majority of them come from distant galaxies (the Milky Way has only one), and they're extraordinarily brilliant, releasing as much energy in a moment as 500 million Suns.

The majority of these eruptions have only been observed once: they appear out of nowhere, explode once, and then vanish. As a result, they're nearly impossible to forecast, as well as trace and examine.

However, a few sources (well, three now) have been identified as reoccurring, providing a tantalizing opportunity to figure out what's going on. Maybe.

The FRB identified in the Milky Way originated from a magnetar, a kind of dead star, implying that magnetar eruptions are responsible for at least some FRBs. However, there are still many unknowns.

"Are those that repeat different from those that don't?" asks West Virginia University astronomer Kshitij Aggarwal.

The FRB 190520B discovery signal was discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China in May of 2019 and found in the data in November of same year.

Following up on the area in the sky, it was discovered that the source was recurring.

The National Science Foundation's Karl G. Jansky Very Large Array was used to undertake more observations, showing an interesting combination of properties. The signals came from the margins of an approximately 4 billion light-year-distance dwarf galaxy.

The source appears to be emitting weaker radio emission in between radio bursts. This implies that the quick radio bursts are generated by a compact persistent radio source whose nature is unknown.

If you're a fan of short radio bursts, you'll recognize this. That's because FRB 121102, another well-known recurring rapid radio burst, has same traits.

This was the first FRB to be linked to a source, the fringes of a 3 billion light-year-distance dwarf galaxy. It, too, is linked to a tiny, long-lasting radio source.

"Now we have two like this, and that brings up some important questions," says Caltech astronomer Casey Law.

We don't know whether one-off FRBs reoccur at energies too low for us to detect, for example. However, scientists have speculated for some time that the bursts may be caused by at least two independent causes, and the finding of FRB 190520B supports this theory.

This might indicate that the distinct bursts are released by different things, or that the same entity is emitting multiple bursts at different phases of its evolution.

Magnetars are a form of neutron star with an extraordinarily intense magnetic field. They are the collapsed, ultra-dense core of a huge star after it has gone supernova and perished. Normal neutron stars and magnetars might both release FRBs in various ways.

Another aspect of rapid radio bursts, according to further investigation, may not be as valuable for gauging the Universe as astronomers may have anticipated.

The dispersion measure is a property that describes how light is dispersed by tenuous gas in the space between us and the source. Higher-frequency waves move more effectively than lower-frequency waves, and this may be used to calculate distance.

The dispersion measure for FRB 190520B indicates that the source is 8 to 9.5 billion light-years distant. Independent distance measurements, on the other hand, reveal that the galaxy isn't that far away.

"This means that there is a lot of material near the FRB that would confuse any attempt to use it to measure the gas between galaxies," Aggarwal explains. "If that's the case with others, then we can't count on using FRBs as cosmic yardsticks." 

On the other hand, this shows that the FRB-emitting persistent radio source is located in a very complicated plasma environment, similar to that of a recent supernova. This implies that whatever the source is, it is a 'newborn' FRB source. 

"We further postulate that FRB 121102 and FRB 190520B represent the initial stage of an evolving FRB population," adds Di Li of the Chinese Academy of Sciences' National Astronomical Observatories.

"A coherent picture of the origin and evolution of FRBs is likely to emerge in just a few years."