How a new radio signal from space baffled the scientist who found it

A new The discovered fast radio burst has some unique properties that both give astronomers important clues as to what might be causing these mysterious astronomical phenomena, while challenging one of the few things scientists thought they knew about these powerful flares, as my colleagues and I describe in a new study in Nature on June 8, 2022.

Fast radio bursts, or FRBs, are extremely bright pulses of radio waves that come from distant galaxies. They release as much energy in a millisecond as the sun does over many days. Researchers here at West Virginia University discovered the first FRB back in 2007. Over the past 15 years, astronomers have discovered around 800 FRBs, and more are being discovered every day.

When a telescope acquires an FRB, one of the most important characteristics researchers look for is something called dispersion. Scatter is basically a measure of how spread out an FRB is when it reaches Earth.

The plasma that lies between stars and galaxies causes all light – including radio waves – to slow down, but lower frequencies feel this effect more and slow down more than higher frequencies. FRBs contain a range of frequencies, so the higher frequency light in the burst hits the ground before the lower frequencies, causing the scattering. This allows researchers to use scattering to estimate how far from Earth an FRB originated. The more extended an FRB, the more plasma the signal must have passed through and the further away the source must be.

At the top of this graph are six peaks in radio wave brightness, which are six bursts from FRB190520. The bottom half shows the frequency range for each individual burst.Niu CH, Aggarwal K, Li D et al.

Why it matters – The new FRB that my colleagues and I discovered is called FRB190520. We found it with the Five-Hundred-Meter Aperture Spherical Telescope in China. One immediately striking interesting thing about FRB190520 was that it is one of only 24 repeating FRBs and repeats much more frequently than others – with 75 outbursts over a six-month period in 2020.

Our team then used the Very Large Array, a radio telescope in New Mexico, to further study this FRB and successfully pinpointed the location of its source – a dwarf galaxy about 3 billion light-years from Earth. That’s when we started to realize how truly unique and important this FRB is.

First, we noticed that a sustained, albeit much weaker, radio signal is being emitted from something originating from the same location that FRB190520 came from. Of the more than 800 FRBs discovered so far, only one other has a similarly persistent radio signal.

Second, we were able to pinpoint how far this galaxy is from Earth because we were able to determine that the FRB came from a dwarf galaxy. But this result made no sense. Much to our surprise, the distance estimate we made using the scattering of the FRB was 30 billion light-years from Earth, a distance 10 times greater than the actual 3 billion light-years to the galaxy.

Astronomers have only been able to pinpoint the exact location — and therefore distance from Earth — of 19 other FRB sources. For the rest of the roughly 800 known FRBs, astronomers have to rely solely on scattering to estimate their distance from Earth. For the other 19 FRBs with known positions, the distances estimated from scattering are very similar to the actual distances to their source galaxies. But this new FRB shows that estimates with variability can sometimes be wrong and throws many assumptions out of whack.

FRB190520 is from a small dwarf galaxy 3 billion light-years away, marked by the crosshairs in the larger inset with the exact location of the FRB source circled in the smaller image.Niu CH, Aggarwal K, Li D et al.

What is not yet known — Astronomers in this new field still don’t know what exactly produces FRBs, so any new discovery or information is important.

Our new discovery raises specific questions, including whether sustained radio signals are common, what conditions produce them, and whether the same phenomenon that creates FRBs is responsible for the sustained radio signal’s emission.

And a big mystery is why FRB190520’s scatter was so much larger than it should be. Was it because of something close to the FRB? Was it related to the permanent radio source? Does it have to do with the matter in the galaxy where this FRB comes from? All of these questions are unanswered.

What’s next – My colleagues will focus on studying FRB190520 using a variety of different telescopes around the world. By examining the FRB, its galaxy, and the space environment surrounding its source, we hope to find answers to many of the mysteries it has revealed.

More answers will also come from other FRB discoveries in the years to come. The more FRBs astronomers catalog, the greater the chances of discovering FRBs with interesting properties that can help complete the puzzle of these fascinating astronomical phenomena.

This article was originally published on The conversation by Kshitij Aggarwal at West Virginia University. Read the original article here.

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