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Monday, November 30, 2020

Explained: What is a radio burst, spotted by NASA for the first time in the Milky Way?

Fast Radio Bursts are bright bursts of radio waves whose durations lie in the millisecond-scale, because of which it is difficult to detect them and determine their position in the sky. 

By: Explained Desk | New Delhi | Updated: November 12, 2020 9:32:28 am
Radio burst, fast radio burst, FRB, milky way, what is FRB, magnetar, express explained, indian expressA powerful X-ray burst erupts from a magnetar - a supermagnetized version of a stellar remnant known as a neutron star - in this illustration. (Photo courtesy: NASA's Goddard Space Flight Center/Chris Smith (USRA)

NASA has reported that on April 28, it observed a mix of X-ray and radio signals never observed before in the Milky Way. Significantly, the flare-up it observed included the first fast radio burst (FRB) seen within the galaxy.

Three papers reporting the detection of the phenomenon called FRB were published in the journal Nature on November 4. So what are FRBs and why is this observation significant?

Who discovered the simultaneous bursts in the Milky Way?

The X-ray portion of the simultaneous bursts was detected by several satellites, including NASA’s Wind mission, and the radio component was discovered by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope located at Dominion Radio Astrophysical Observatory in British Columbia, which is led by McGill University in Montreal, the University of British Columbia, and the University of Toronto.

Further, a NASA-funded project called Survey for Transient Astronomical Radio Emission 2 (STARE2) also detected the radio burst seen by CHIME. STARE2 is operated by Caltech and NASA’s Jet Propulsion Laboratory in Southern California and the team behind it determined that the burst’s energy was comparable to FRBs.

So what is an FRB?

The first FRB was discovered in 2007, since when scientists have been working towards finding the source of their origin. Essentially, FRBs are bright bursts of radio waves (radio waves can be produced by astronomical objects with changing magnetic fields) whose durations lie in the millisecond-scale, because of which it is difficult to detect them and determine their position in the sky.

What is the origin of the FRB detected in April?

The source of the FRB detected in April in the Milky Way is a very powerful magnetic neutron star, referred to as a magnetar, called SGR 1935+2154 or SGR 1935, which is located in the constellation Vulpecula and is estimated to be between 14,000-41,000 light-years away.

The FRB was part of one of the magnetar’s most prolific flare-ups, with the X-ray bursts lasting less than a second. The radio burst, on the other hand, lasted for a thousandth of a second and was thousands of times brighter than any other radio emissions from magnetars seen in the Milky Way previously. It is possible that the FRB-associated burst was exceptional because it likely occurred at or close to the magnetar’s magnetic pole.

This flare-up, which lasted for hours, was picked up by NASA’s Fermi Gamma-ray Space telescope and NASA’s Neutron star Interior Composition Explorer (NICER), which is an X-ray telescope mounted on the International Space Station. 📣 Express Explained is now on Telegram

What is a magnetar?

As per NASA, a magnetar is a neutron star, “the crushed, city-size remains of a star many times more massive than our Sun.” The magnetic field of such a star is very powerful, which can be over 10 trillion times stronger than a refrigerator magnet and up to a thousand times stronger than a typical neutron star’s.

Neutron stars are formed when the core of a massive star undergoes gravitational collapse when it reaches the end of its life. This results in the matter being so tightly packed that even a sugar-cube sized amount of material taken from such a star weighs more than 1 billion tons, which is about the same as the weight of Mount Everest, according to NASA.

Magnetars are a subclass of these neutrons and occasionally release flares with more energy in a fraction of a second than the Sun is capable of emitting in tens of thousands of years. In the case of SGR 1935, for instance, the X-ray portion of the simultaneous bursts it released in April carried as much energy as the Sun produces in a month, assuming that the magnetar lies towards the nearer end of its distance range.

Why is this observation significant?

Until now, there were various theories that tried to explain what the possible sources of an FRB could be. One of the sources proposed by the theories has been magnetars. But before April this year, scientists did not have any evidence to show that FRBs could be blasted out of a magnetar. Therefore, the observation is especially significant.

Chris Bochenek, a doctoral student of astrophysics at Caltech, was quoted as saying in a NASA press release, “While there may still be exciting twists in the story of FRBs in the future, for me, right now, I think it’s fair to say that most FRBs come from magnetars until proven otherwise.”

“Taken together, the observations strongly suggest that SGR 1935 produced the Milky Way’s equivalent of an FRB, which means magnetars in other galaxies likely produce at least some of these signals,” NASA has said.

Even so, for an “ironclad proof” of FRBs connection with magnetars, researchers will continue to look for an FRB outside of the Milky Way that coincides with an X-ray burst from the same source.

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