Fast radio bursts (FRBs) are intense, short-lived bursts of radio waves coming from beyond the Milky Way that can emit the same amount of energy as the sun takes in three days in just a thousandth of a second.
However, despite their power and the fact that around 10,000 FRBs can explode in the sky above Earth every day, these radio bursts remain mysterious. One of the biggest puzzles surrounding FRBs is why most blink once and then disappear, while a tiny minority (less than 3 percent) blink again. This has led scientists to search for the mechanisms that trigger FRBs. Some even believe that various celestial objects can produce both repeating and non-repeating FRBs.
Using the Canadian Hydrogen Intensity Mapping Experiment (CHIME), scientists from the University of Toronto looked at the properties of the polarized light associated with 128 non-repeating FRBs. This revealed that one-off FRBs appear to originate from distant galaxies that are very similar to our own Milky Way, as opposed to the extreme environments that emit their recurring relatives. The results could finally bring scientists closer to solving the enduring FRB celestial puzzle.
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“Until now, when we’ve thought about FRBs, we’ve only looked at them in the same way we’d look at a star in the sky, thinking about how bright it is, maybe figuring out how far away it is, things like that,” lead author research by Ayush Pandhi, Ph.D. student at the Dunlap Institute for Astronomy & Astrophysics and the David A. Dunlap Department of Astronomy & Astrophysics at the University of Toronto, told Space.com. “However, FRBs are special because they also emit polarized light, meaning that the light coming from these sources is oriented in one direction.”
The key difference in this research is that it actually looked at polarized light.
Polarized light consists of waves that are oriented in the same way – vertically, horizontally, or at an angle between the two directions. Polarization changes could explain the mechanism that triggered the FRB and thus reveal what its source was. Polarization can also reveal details about what environments the FRB had to pass through before reaching our detectors on Earth. This study represented the first large-scale view of the non-repeating 97% of FRBs in polarized light.
There has been a gap in the research on non-recurring FRBs because it is much easier to observe recurring FRBs because astronomers already know where they will occur, meaning it is possible to point any radio telescope at that patch of sky and wait. With non-recurring FRBs, astronomers must have a telescope that can look at a large area of ​​the sky at once because they don’t really know where the signal is coming from.
“They could appear anywhere in the sky. CHIME is unique in that sense because it looks at such a large chunk of the sky at once,” Pandhi said. “People haven’t really looked at this polarization yet because it’s much harder to detect just on a technical level.
“Other studies have looked at the polarization of maybe 10 non-recurring FRBs, but this is the first time we’ve looked at more than 100. It allows us to rethink what we think FRBs are and see how recurring and non-recurring FRBs can be different .”
To repeat or not to repeat?
In 2007, astronomers Duncan Lorimer and David Narkevic, who was Lorimer’s student at the time, discovered the first FRB. It was a non-repeating burst of energy now commonly called the “Lorimer Burst.” Five years later, in 2012, astronomers discovered the first recurring FRB: FRB 121102. After that, other recurring bursts were gradually detected.
Naturally, astronomers are interested in whether there is another phenomenon behind these two types of FRBs. And Pandhi’s team actually found that non-recurring FRBs appear to be a bit different from recurring FRBs, since most of them come from galaxies like our own Milky Way.
While the origin of FRBs is shrouded in mystery, these bursts of radio waves may act as messenger mediums that they pass through as they race to Earth. This information is encoded in their polarization.
“If polarized light passes through electrons and magnetic fields, the angle at which it is polarized rotates, and we can measure this rotation,” Pandhi said. less, it will spin less.”
The fact that the polarization of non-repeating FRBs is smaller than that of repeating FRBs suggests that the former pass through less massive or weaker magnetic fields than the latter. Pandhi added that while repeated bursts of radiation appear to come from more extreme environments (such as the remnants of stars that died in supernova explosions), their non-recurring brethren apparently appear in slightly less violent environments.
“Non-recurring FRBs tend to come from environments that have either weaker magnetic fields or less stuff around them than recurring FRBs,” Pandhi continued. “So the FRB repeat seems to be a bit more extreme in that sense.”
Are neutron stars out of reach?
One of the big surprises that this research brought to Pandhim was that the polarization of non-recurring FRBs seemed to shed light on one of the main suspects behind their launch: highly magnetized, rapidly rotating neutron stars, or “pulsars.”
“We know how pulsars work and we know the types of polarized light we expect from a pulsar system. Surprisingly, we don’t see that much similarity between FRBs and pulsar light,” Pandhi said. “If these things come from the same type of object, you might expect them to have some similarities, but they appear to be actually quite different.”
When it comes to figuring out what objects emit FRBs, Pandhi thinks expanding our understanding of the polarization of these radio wave bursts could help narrow down theoretical predictions.
“If we’re confused between multiple different theories, we can now look at polarized light and say, ‘Okay, okay, does this rule out any theories that we haven’t already ruled out?'” he said. “It provides another parameter, or even several more parameters, to help us rule out theories about what they could be until we have one that sticks.”
Pandhi went on to explain that this study laid the groundwork for future investigations of FRBs; he himself is working on a way to separate the polarization of FRBs that occurred in the Milky Way from those that occurred in their other galaxies and closer to the source of their emission.
This should help us better understand the mechanisms behind the release of FRBs, but for Pandhi, it’s the mysterious nature of these cosmic bursts of energy that ensures he’ll be investigating them for some time to come.
“I mean, what’s more mysterious than explosions happening thousands of times a day all over the sky, and you have no idea what’s causing them?” Pandhi said. “If you’re a bit of a detective who likes to solve mysteries, FRBs are just a mystery just begging to be solved.”
The team’s research was published Tuesday (June 11) in the Astrophysical Journal.