Strange Radio Burst From Space Intrigues Astronomers

The radio bursts are only the second example of a highly active, repeating fast radio burst (FRB) with a compact source of weaker but persistent radio emission between bursts.

Strange radio bursts from space have intrigued astronomers. These radio bursts are only the second example of a highly active, repeating fast radio burst (FRB) with a compact source of weaker but persistent radio emission between bursts. The study describing the findings was recently published in the journal Nature.

The discovery of the radio bursts raises new questions about the nature of these mysterious objects. Astronomers are wondering if these objects could prove to be useful for studying the nature of intergalactic space. The researchers who conducted the study used the National Science Foundation's Karl G. Jansky Very Large Array (VLA) and other telescopes to study the object which released the fast radio burst. The object, called FRB 190520, was first discovered in 2019. 

When Was FRB 190520 Discovered?

FRB 190520 was found by the Five-hundred-metre Aperture Spherical radio Telescope (FAST) in China, and a burst from it occurred on May 20, 2019. The burst was found in data from the telescope in November 2019. The object, unlike other fast radio bursts, emits frequent, repeating bursts of radio waves, follow-up observations with FAST revealed. 

Where Is The Object Located?

In 2020, astronomers found the object's location using the VLA. Visible-light observations with the Subaru telescope in Hawaii showed that the object is in the outskirts of a dwarf galaxy nearly three billion light-years from Earth. The object constantly emits weaker radio waves between bursts, the VLA observations suggest.

When Was The First Fast Radio Burst Discovered?

In a statement released by the National Radio Astronomy Observatory, Casey Law, a researcher at the California Institute of Technology, said these characteristics make the object look a lot like the very first FRB whose position was determined, also by the VLA, back in 2016. The discovery of the very first FRB was a major breakthrough because it provided the first information about the environment and distance of an FRB. The combination of repeating bursts and persistent radio emission between bursts, coming from a compact region, set the 2016 project, known as FRB 121102, apart from all other known FRBs, until now.

The Two Fast Radio Bursts Raise Important Questions

Law said now there are two such fast radio bursts, and that brings up some important questions.

According to the study, the difference between FRB 190520 Nd FRB 121102 and all others strengthen a possibility that there may be two different kinds of FRBs. 

Two Different Mechanisms Produce FRBs

There may be either two different mechanisms producing FRBs or the objects producing them may act differently at different stages of their evolution, astronomers suggest. Super dense neutron stars left over after a massive star explodes as a supernova, or neutron stars with ultra-strong magnetic fields, called magnetars, are the leading candidates for the sources of FRBs.

According to the astronomers, one characteristic of FRB 190520 calls into question the usefulness of FRBs as tools for studying the material between them and Earth. The effects of intervening material on the radio waves emitted by distant objects helps astronomers learn about the tenuous material itself. When radio waves pass through space that contains free electrons, the high-frequency waves travel more quickly than lower-frequency waves.

What Is The Dispersion Effect?

This effect is known as dispersion, and can help determine the density of electrons in the space between the object and Earth. If the electron density is known or assumed, 'dispersion' can provide a rough estimate of the distance to the object. The distance between pulsars and the Earth can also be estimated with the help of this effect.

Dispersion Effect Did Not Work For FRB 190520

However, the effect did not work for FRB 190520. The distance of the object from Earth was measured on the basis of the Doppler shift of the host galaxy's light caused by the expansion of the universe. This placed the galaxy at nearly three billion light-years from Earth. Doppler shift or Doppler effect is the change in the wavelength of frequency of waves with respect to the observer who is in motion relative to the wave source.

However, the researchers noted in the study that the burst's signal shows an amount of dispersion that ordinarily would indicate a distance of roughly eight to 9.5 billion light-years. 

Can FRBs Be Considered Cosmic Yardsticks?

According to one of the researchers, 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 the galaxies. FRBs cannot be considered as cosmic yardsticks if that is the case with others.

The astronomers noted in the study that FRB 190520 may be a "newborn", still surrounded by dense material ejected by the supernova explosion that left behind the neutron star. The dispersion of the burst signals would decline as the material eventually dissipates. The astronomers said that under the "newborn" scenario, the repeating bursts also might be a characteristic of younger FRBs and dwindle with age.

Sarah Burke Spolaor, one of the authors on the paper, said the FRB field is moving very fast right now and new discoveries are coming out monthly. She added big questions still remain, and that the object is giving astronomers challenging clues about those questions.