Astronomers have used two of the world’s largest radio telescopes to discover the second-known example of a new type of fast radio burst (FRB) — the mysterious, extremely powerful bursts of radio waves that pulse through space thousands of times a day.
The new FRB, designated FRB 190520, is strong evidence that multiple celestial objects could be the source of these enigmatic signals.
The new object is the second to be discovered, which not only produces repetitive FRBs but also emits a constant source of weaker radiation between eruptions. The signal was detailed in an article published in the journal on June 8 Nature.
First discovered in 2007, rapid radio bursts release more energy in a few short milliseconds than the sun does in a year. Astronomers have long puzzled over the source of these sudden bright flashes. But that’s when they mostly break out galaxies millions or even billions light years gone, and flare up quickly and often only once, it is very difficult to identify their sources.
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In 2020, the first-ever discovery of an FRB in our own galaxy allowed scientists to trace its origin to a magnetar — a highly magnetized, rapidly rotating shell of a dead star. Magnetars are a special kind of neutron star, which are ultradense stellar bodies left behind by supernova explosions. Magnetars have unusually strong magnetic fields, trillions of times stronger than Earth’s. However, scientists are not sure if all FRBs are from magnetars.
Stranger still, the flashes from some FRBs repeat themselves—sometimes in a single brief burst, and sometimes across multiple sporadic iterations. Of these repeating FRBs, FRB 121102 is the first and most active. The unknown source, located in a dwarf galaxy 3 billion light-years away, spews radio waves out of a compact region over a 157-day cycle; It alternates between 90 days of strong, repetitive radio bursts and 67 days of gentler, weaker radio emissions. FRB 121102 is very active (burping has been recorded 1,652 torches over a 47-day period) and for a while astronomers thought it was the only one of its kind, until now.
Researchers got their first glimpses of the new fast radio burst FRB 190520 with China’s Five Hundred Meter Aperture Spherical Radio Telescope (FAST). FAST confirmed that the distant object was emitting frequent and repetitive radio bursts, and later observations made with New Mexico’s Very Large Array (VLA) pinpointed its location. Scientists found that the source of the repeating outbursts, similar to its cousin, was in a dwarf galaxy about 3 billion light-years from Earth. The VLA also confirmed that FRB 190520’s source was small and compact, and that it emitted weaker radio emissions between larger flashes.
The arrival of a second FRB with similar behavior to the first raises some important questions and raises the possibility that there could be two different types of FRB, the scientists say.
“Are those who repeat different from those who don’t? What about the ongoing radio emission—is that common?” Study co-author Kshitij Aggarwal, an astronomer and graduate student at West Virginia University said in a statement.
Astronomers believe that either two or more entirely different mechanisms exist to create these stunning cosmic flashes, or that the bursts are produced by objects at very different stages in their cosmic evolution.
Some indirect evidence supports the second hypothesis. Because FRBs often arrive as single pulses of unknown origin, astronomers typically estimate how far the source is from Earth by measuring how much the radio waves emitted by an FRB are separated by frequency (like light after it’s passed through a prism ) – something that happens to them the more often they encounter free electrons in space. The effect, called dispersion, gives astronomers a good approximate estimate of how far a radio burst has traveled before reaching telescopes on Earth, assuming electrons are fairly evenly distributed in space.
But being able to track the location of FRB 190520’s source revealed a strange discrepancy. The pulsating object’s radio waves were scattered enough to originate from about 8 to 9.5 billion light-years away, but by studying the Doppler shift, or the stretching of radio wave wavelengths caused by the expansion of the universe, the Astronomers more precisely placed the object just under 3 billion light-years from Earth.
“This means there is a lot of material near the FRB that would confound any attempt to use it to measure the gas between galaxies,” Aggarwal said. “If that’s the case with others, then we can’t rely on using FRBs as cosmic yardsticks.”
The unusually dense electron clouds surrounding the FRB could indicate that the source is a ‘newborn’ magnetar, still encased in material from the supernova explosion that produced it. But researchers will need many more measurements before they can be sure.
“The FRB field is currently moving very rapidly and new discoveries are coming out monthly. However, big questions remain, and this object provides us with challenging clues to those questions,” co-author Sarah Burke-Spolaor, assistant professor of astronomy at West Virginia University, said in the statement.
Originally published on Live Science.
https://www.livescience.com/second-repeating-fast-radio-burst-found Weird type of fast radio burst discovered 3 billion light-years away