This article was updated on January 11, 2019 with comment from paper author Cherry Ng.
In 2007, radio astronomers discovered what they love most: a mystery.
Two researchers, combing the archives of the Parkes Observatory in Australia, found a radio signal the observatory recorded six years prior, but that nobody had noticed. It was fast—just a matter of milliseconds—but what impressed them was the power behind the signal, emitting 500 times the energy of the sun.
Since then, astronomers have sought to find out what's causing these enigmatic bursts. Maybe it's black hole and neutron star collisions. Maybe something at the centers of galaxies is falling into a supermassive black hole just right. Or maybe it's dark matter interacting with pulsars, causing an energetic collapse. None of these theories can really be tested yet because there's been one problem with studying fast radio bursts: Most of them are one and done, detected and then gone in an instant.
A new set of papers published today in , however, could bring the answer just a little bit closer. For only the second time, researchers have found a fast radio burst source that repeats its signal. The repeater burst comes as part of a series of 13 new fast radio bursts (FRB) found by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) collaborators.
The new burst, FRB 180814.J0422+73, was discovered in the summer of 2018, before CHIME was fully online. Once CHIME was fully up and running, it heard the source a handful more times, always coming from the same direction of the sky, though astronomers are still trying to pinpoint an exact source. Only one other repeating FRB is known, FRB 121102. It was originally detected in 2012 and confirmed to repeat in 2015.
"So far they actually look quite similar in some sense," Cherry Ng, a CHIME researcher based out of the University of Toronto's Dunlap Institute and author on the paper, says. "They both have a lot of temporal structure in the way they bursts, which is actually curious because most of the other non-repeating FRBs don't look like that. The second repeater appears to be quite a bit close to us."
Ng says this particular repeater appears to be about 1.5 billion light years from us—so beyond our local supercluster, but "close" compared to other galaxies. While the bursts repeat, they don't have a period to them—meaning that whatever event causes them seems to cause them under certain, quasi-random conditions. "It is likely that the environment that they come from are not totally 'calm,' but somewhat dynamic, with relativistic plasma surrounding a compact object for example, or perhaps similar to solar radio bursts," Ng says.
Astronomers are still trying to figure out what is causing the phenomena. The duration of the bursts suggests that it's a small source, while the way the radio bursts "scatter" suggest they're taking place inside an extreme environment, like a black hole or neutron star. It's even been suggested that the origin could be dense objects like those colliding.
To really figure out what the heck is going on, astronomers will need to find additional sources that repeat so they can compare them to each other—and, maybe, to find some other event (like a visible light burst) that ties the radio signal to a specific location in the universe and gives clues to what else is happening in the region.
"With the currently small number of repeaters known, and the fact that we still don't know what are the progenitors of FRB, it is hard to say," Ng says. "We definitely hope to find more more FRBs with CHIME this year, and with a large population of FRBs, we sure be able to tease out any differences between repeating and non-repeating sources."
For now, all we have is two repeating sources and several dozen outliers—but at least it's a good start.