Nov 6, 2020

Scientists detect strange 'fast radio burst' from within our own Milky Way



Mysterious superpowerful blasts of radio waves once seen only outside the galaxy  have for the first time been detected within the Milky Way, new studies find.

In addition, scientists have traced these outbursts back to a rare kind of dead star known as a magnetar, the strongest magnets in the universe, for the first time.

Fast radio bursts, or FRBs, are intense pulses of radio waves that can release more energy in a few thousandths of a second than the sun does in nearly a century. Scientists only discovered FRBs in 2007, and because the bursts are so fast, astrophysicists still have many questions about them and their sources.

Scientists have dozens of theories about the causes of fast radio bursts, from colliding black holes to alien starships. Many theories suggest the bursts originate from neutron stars, which are corpses of stars that died in catastrophic explosions known as supernovas. (Their name comes from how the gravitational pulls of these stellar remnants are powerful enough to crush protons together with electrons to form neutrons.)

Video: Magnetar blasts fast radio burst in Milky Way?


An artist's impression of a magnetar in outburst, showing complex magnetic field structure and beamed emission following a crust-cracking episode. (Image credit: McGill University Graphic Design Team)

Specifically, previous research has suggested fast radio bursts might explode from a rare type of neutron star known as a magnetar. Magnetars are the most powerful magnets in the cosmos — their magnetic fields can be up to approximately 5,000 trillion times more powerful than Earth's. 

"A magnetar is a type of neutron star whose magnetic fields are so strong, they squish atoms into pencil-like shapes," Christopher Bochenek, an astrophysicist at the California Institute of Technology in Pasadena and lead author on one of the new studies, told Space.com.Scientists had suspected magnetars might generate fast radio bursts because prior work found that magnetars could erupt giant flares of gamma rays and X-rays. These giant flares "have a very short duration, a hard spike that lasts for milliseconds, and that is exactly the duration of FRBs," Bing Zhang, an astrophysicist at the University of Nevada, Las Vegas and coauthor on one of the new studies, told Space.com. As such, researchers had suggested they might produce short powerful bursts of radio waves as well.

In the new studies, scientists reported that on April 28, two radio telescopes — the Survey for Transient Astronomical Radio Emission 2 (STARE2) array of three radio antennas in California and Utah, and the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope in Okanagan Falls, Canada — detected a fast radio burst dubbed FRB 200428. 

"This is the most luminous radio burst ever detected in our own galaxy," Daniele Michille, an astrophysicist with CHIME and coauthor on one of the new studies, told Space.com. In the fraction of a second that this fast radio burst flashed, it was 3,000 times brighter than any other magnetar radio signal observed to date, the researchers noted.Both arrays located the FRB in the same area of the sky. "This burst was so bright that in theory, if you had a recording of the raw data from your cell phone's 4G LTE receiver, which does detect radio waves, and if you knew what you were looking for, you might have found this signal that came from about halfway across the galaxy in your cell phone data," Bochanek said.

The scientists pinpointed the outburst to a magnetar known as SGR 1935+2154, located about 30,000 light-years from Earth towards the galaxy's center in the constellation Vulpecula. This is the closest known FRB to date.

"We were able to determine that the energy of this burst is comparable to the energies of extragalactic fast radio bursts," Bochanek added. "In about 1 millisecond, the magnetar emitted as much energy in radio waves as the sun does in 30 seconds."

All in all, "we were able to determine the rate of these bright bursts from magnetars is consistent with the known rate of extragalactic fast radio bursts," Bochenek said. "This discovery therefore paints the picture that some, and perhaps most, fast radio bursts from other galaxies also originate from magnetars."

A fast radio burst mystery

Astronomers led by Zhang compared the observations with data gathered by the Five-hundred Meter Aperture Spherical Telescope (FAST) in China and did see 29 energetic gamma-ray bursts from this magnetar, but none of these coincided with any FRB seen from the magnetar. The disconnect may suggest that gamma-ray bursts from magnetars that give rise to FRBs are very special in some way, with most not doing so, Zhang said. Another possibility is that any FRBs such gamma-ray bursts generate are emitted in narrow beams pointed away from Earth, he noted.

Zhang noted there are two kinds of sources of fast radio bursts — ones that regularly generate FRBs, and ones that produce FRBs less often. If both types of fast radio burst sources are found among magnetars, that suggests two kinds of magnetars may exist: One is the kind of magnetar found in the Milky Way, which infrequently generates FRBs, and the other is more active, and perhaps consisting of newly born, rapidly rotating magnetars, Zhang said.

Future research on FRBs can pinpoint the mechanism through which magnetars or other possible bodies generate these outbursts, Zhang said. 

One possibility involves randomly moving high-energy electrons generating radio waves as they interact with magnetic fields — supermassive black holes, supernova remnants and hot gas sitting in galaxies often generate radio waves this way. Another potential explanation, which Zhang favored, involves electrons as they interact en masse with magnetic fields, similar to how electronics on Earth generate radio waves by directing electrons through a wire.

Bochenek, Michille, Zhang and their colleagues detailed their findings in three studies published in the Nov. 5 issue of the journal Nature

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