Astronomers discover mysterious recurring streams of radio waves from outer space

Artist’s conception of a neutron star with an ultra-strong magnetic field, called a magnetar, emitting radio waves (red). Magnetism is a prime candidate for what generates fast radio bursts. Credit: Bill Saxton, NRAO/AUI/NSF

In radio astronomy, a fast radio burst (FRB) is a transient radio pulse ranging in length from a fraction of a millisecond to a few milliseconds in length, caused by some as-yet-undiscovered mysterious high-energy astrophysical process. Astronomers estimate that the average FRB releases energy in one thousandth of a second (thousandth of a second) as the Sun extinguishes it in 3 days (which is well over 250,000 seconds).

Duncan Lorimer and his student David Narkevich discovered the first FRB in 2007, known as Lorimer Burst. Since then, many others FRBs It has been discoverer. one of these, FRB 180916he is until far away mysterious Because he beat on me regular base Every 16.35 days.

Now, astronomers have found only the second example of a repetitive, highly energetic fast radio burst with a compressed source of weaker but continuous radio emission between bursts. The discovery raises new questions about the nature of these mysterious objects as well as their usefulness as tools for studying the nature of intergalactic space. The scientists used the Karl G.

The object, called FRB 190520, was found by the Five Hundred Meter Aperture Spherical Radio Telescope (FAST) in China. An explosion from the object occurred on May 20, 2019, and was found in data from this telescope in November of that year. Follow-up observations with FAST showed that, unlike many other FRBs, it emits frequent, repetitive bursts of radio waves.

VLA image of the Fast Radio Burst FRB 190520 (red), along with the optical image, when the FRB explodes. Credit: Niu et al.; Bill Saxton, NRAO/AUI/NSF; CFHT

Observations using the VLA in 2020 determined the location of the object, which allowed visible-light observations with the Subaru Telescope in Hawaii to show that it is located in the outskirts of a dwarf galaxy about 3 billion light-years from Earth. The VLA’s observations also found that the body constantly emits weaker radio waves between bursts.

“These characteristics make this person look very much alike The first FRB to be located — also by the VLA — in 2016, “said Casey Law, of Caltech. This development was a major breakthrough, providing the first information about the environment and distance of the FRB. However, a combination of frequent bursts and continuous radio emissions between bursts, the upcoming From a compressed region, it identified the 2016 object, named FRB 121102, apart from all other known FRBs, so far.

FRB 190520 region, seen in visible light, with VLA image of a fast radio burst moving between an object’s explosion and non-explosion. Credit: Niu et al.; Bill Saxton, NRAO/AUI/NSF; CFHT

“We now have two like this, and that raises some important questions,” Lu said. Law is part of an international team of astronomers publishing their findings in the journal temper nature.

The differences between FRB 190520, FRB 121102 and all the others reinforce the previously suggested possibility that there may be two different types of FRBs.

“Are those that repeat different than those that don’t? What about continuous radio emission — is this common?” said Kshitij Aggarwal, a graduate student at West Virginia University (WVU).

Astronomers suggest that there may be two different mechanisms for producing FRBs or that the organisms that produce them may function differently at different stages of their development. The main candidates for FRBs are the super-dense neutron stars left after the explosion of a massive star in the form of a supernova, or neutron stars with ultra-strong magnetic fields, called magnetars.

The location of FRB 190520 in the sky. Credit: Bill Saxton, NRAO/AUI/NSF

A feature of FRB 190520 calls into question the usefulness of FRBs as tools for studying materials between them and the Earth. Astronomers often analyze the effects of interfering material on radio waves emitted by distant objects to identify this same weak material. One such effect occurs when radio waves pass through space containing free electrons. In this case, high-frequency waves travel faster than low-frequency waves.

This effect, called scattering, can be measured to determine the density of electrons in the space between an object and the Earth, or if the electron density is known or assumed, you can provide a rough estimate of the distance to the object. The effect is often used to make estimates of the distance of pulsars.

That didn’t work with FRB 190520. An independent measurement of distance based on the Doppler shift of galactic light caused by the expansion of the universe put the galaxy 3 billion light-years away from Earth. However, the splash signal shows an amount of scattering that typically indicates a distance of about 8 to 9.5 billion light-years.

“This means that there is a lot of material near the FRB that would confuse any attempt to use it to measure intergalactic gas,” Aggarwal said. “If this is the case with others, we cannot rely on the use of FRBs as cosmological scales,” he added.

Astronomers have speculated that FRB 190520 may be ‘newborn’, still surrounded by dense material from the supernova explosion left behind.[{” attribute=””>neutron star. As that material eventually dissipates, the dispersion of the burst signals also would decline. Under the “newborn” scenario, they said, the repeating bursts also might be a characteristic of younger FRBs and dwindle with age.

“The FRB field is moving very fast right now and new discoveries are coming out monthly. However, big questions still remain, and this object is giving us challenging clues about those questions,” said Sarah Burke-Spolaor, of WVU.

Reference: “A repeating fast radio burst associated with a persistent radio source” 8 June 2022, Nature.
DOI: 10.1038/s41586-022-04755-5

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.