In a dwarf galaxy 3 billion light-years away, something goes thump in the night. Fast radio bursts, or FRBs, have perplexed astrophysicists for years, but a new study could solve the mystery of these high energy bursts of radio waves detected across the universe.
In research published today in Nature and also presented at the 231st meeting of the American Astronomical Society, a consortium of international researchers operating radio telescopes around the world are nearing an explanation for the only known fast radio burst to regularly repeat. FRBs are strong radio signals lasting a small fraction of a second that were first discovered in 2012. Since then, astronomers have struggled to find an explanation for what could be causing such a short-lasting, high-energy phenomenon.
Then they found FRB 121102.
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FRB 121102 is a fast radio burst emitter unlike any other discovered. While many FRBs appear to be one-and-done, 121102 periodically repeats. That has given researchers a perfect laboratory to research these bursts by localizing a place to look and listen.
"Now you can point any telescope at this sort, and know you’re pointing at the source," Betsey Adams of the Netherlands Institute for Radio Astronomy said at an AAS press conference.
The prevailing theory (though it's far from confirmed) is that neutron stars, the leftover cores of giant stars that have undergone supernovae explosions, are causing the bursts. Based on the duration and strength of the burst, it's been pinpointed in a roughly a six mile area in its far-away galaxy. Neutron stars are roughly that size, with the entire mass of the sun (or more) compacted into the size of a medium-sized city.
The area is riddled with highly magnetized, hot gas often seen near black holes—which could be one catalyst of the bursts.
Many neutron stars rotate rapidly and emit regular radio waves, and the objects that do are called pulsars. The researchers believe that FRB 121102 could be a young neutron star enshrouded by gas and dust from the preceding supernova explosion. That environment could be the breeding ground for the fast radio bursts as the star interacts with the dust.
"It’s hard to explain with the source," Vishal Gajjar of the Breakthrough Listen initiative said. "It’s easier to explain if it has something to do with the environment."
The theory still has some unexplained mysteries, however. Pulsars keep time like a metronome, but the detected fast radio bursts from 121102 don't appear (yet) to come at regular intervals. In five hours of observations, the first hour yielded 18 radio bursts—and the subsequent four hours revealed nothing.
One possibility is that there is some kind of lensing event that causes these bursts to point toward the observer at differing intervals. Once that focal point is out of range, the signals aren't sufficiently amplified to be further detected.
To dig further in, researchers will use several next-generation telescopes with several complicated acronyms (CHIME, ASKAP, UTMOST, and APERTIF) to provide a broader coverage area for fast radio bursts. These observatories will keep a constant ear on FRB 121102 while also scanning the skies for more repeating sources.
The new radio observatories will also be able to make out the finer structures of the bursts, which even at 121102 don't appear to be uniform in structure (which could also be a product of the surrounding environment).
Before you jump to conclusions: No one thinks it's aliens right now.
"I don’t think we’re really thinking in that direction," said Gajjar, whose organization is one of the leading groups performing the Search for Extraterrestrial Intelligence (SETI).
Score one for team neutron star.