Kshitij Aggarwal (opens in new tab)associate researcher in astronomy and astrophysics, West Virginia University
A newly discovered fast radio burst has some unique properties that simultaneously give astronomers important clues as to what may be triggering these mysterious astronomical phenomena, while also casting doubt on one of the few things scientists thought they knew about these powerful flares, like my colleagues. and I describe in a new study (opens in new tab) in nature on June 8, 2022.
Fast radio bursts, or FRBs, are extremely bright pulses of radio waves coming from far away galaxies† They release as much energy in a millisecond as the sun is doing for many days (opens in new tab)† Researchers here at West Virginia University discovered the first FRB in 2007 (opens in new tab)† In the past 15 years, astronomers have detected about 800 FRBs, with more is being discovered every day (opens in new tab)†
When a telescope captures an FRB, one of the main features that researchers look at is something called dispersion. Dispersion is basically a measure of how stretched an FRB is when it reaches Soil†
The plasma that sits between stars and galaxies causes all light — including radio waves — to slow down, but lower frequencies feel this effect more strongly and slow down more than higher frequencies. FRBs contain a range of frequencies, so the higher-frequency light in the burst hits the Earth earlier than the lower frequencies, causing the dispersion. This allows researchers to use scatter to estimate how far from earth did an FRB originate? (opens in new tab)† The more an FRB is stretched, the more plasma the signal must have passed through, the further away the source must be.
Why it matters
The new FRB my colleagues and I discovered hot FRB190520 (opens in new tab)† We found it using the Spherical telescope with an aperture of 500 meters (opens in new tab) in China. An immediately obviously interesting aspect of FRB190520 was that it is one of only 24 repeating FRBs and is repeated much more often than others – with 75 bursts in a six month time frame in 2020.
Our team then used the Very large array (opens in new tab)a radio telescope in New Mexico, to further study this FRB and successfully determine the location of the source – a dwarf galaxy about 3 billion light years from earth. Then we started to realize how unique and important this FRB is.
First, we found that there is a persistent, though much weaker, radio signal is broadcast (opens in new tab) by something from the same place FRB190520 came from. of the more than 800 FRBs discovered so far (opens in new tab)only one other has a similar persistent radio signal.
Second, because we were able to determine that the FRB came from a dwarf galaxy, we were able to determine exactly how far away that galaxy is from Earth. But this result was wrong. To our surprise, the distance estimate we made using the FRB’s dispersion was 30 billion light-years from Earth, a distance 10 times larger than the actual 3 billion light-years to the galaxy (opens in new tab)†
Astronomers have only been able to determine the exact location – and thus the distance from Earth – from 19 other FRB sources (opens in new tab)† For the rest of the roughly 800 known FRBs, astronomers must rely solely on dispersion to estimate their distance from Earth. For the other 19 FRBs whose locations are known, the estimated distances based on dispersion are very similar to the actual distances from their source galaxies. But this new FRB shows that scatter estimates can sometimes be inaccurate and throws many assumptions out the window.
What is not yet known
Our new discovery raises specific questions, including whether persistent radio signals are common, under what conditions they are produced, and whether the same phenomenon that produces FRBs is responsible for transmitting the persistent radio signal.
And a huge mystery is why FRB190520’s spread was so much bigger than it should be. Was it something close to the FRB? Was it related to the persistent radio source? Does it have to do with the matter in the galaxy where this FRB comes from? All these questions are unanswered.
My colleagues are going to focus on studying FRB190520 with a wide variety of telescopes around the world. By studying the FRB, its galaxy and the space environment around its source, we hope to find answers to many of the mysteries it has revealed.
There will also be more answers from other FRB discoveries in the coming years. The more astronomers catalog FRBs, the more likely they are to discover FRBs with interesting properties that could help complete the puzzle of these fascinating astronomical phenomena.
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