Fast radio bursts, powerful pulses of radio energy of unknown cosmic origin, are a source of endless fascination to astronomers and alien conspiracy theory fodder to everybody else. But while most FRBs discovered to date are one-off events — a single chirp in the interstellar void, if you will — these phenomena got more interesting last year when astronomers discovered the very first FRB signal that repeats. Now, they have pinpointed its location.
Artist's impressing of the dishes of the Very Large Array localizing a fast radio burst in space for the first time. Image: Danielle Futselaar
FRB 121102, the only repeating fast radio burst know to science, is located over three billion light years away, in a dwarf galaxy a thousand times dimmer than the Milky Way, according to new research published today in Nature. Not only does the new analysis confirm that mysterious radio bursts emanate from a source far beyond our galaxy, zeroing in on their location means we can start unravelling what exactly that source is.
All we know at this point is that FRBs are coming from something powerful. "These radio flashes must have enormous amounts of energy to be visible from over 3 billion light-years away," Cornell astronomer and lead study author Shami Chatterjee said in a statement.
"I think this is a really big deal, and I'm really excited about the result," Peter Williams, an astronomer at Harvard's Center for Astrophysics who was not involved with the study, told Gizmodo.
Over the past decade, astronomers have catalogued more than a dozen FRBs, seemingly random flashes of radio energy that appear in the sky at far-flung locations and then disappear. FRB 121102 was first spotted in 2012 at the Arecibo Observatory in Puerto Rico, one of the world's most powerful radio telescopes. But unlike earlier FRBs, 1211102 wasn't just a flash in the pan: Follow-up observations in 2015 revealed 10 additional radio bursts emanating from the same region of space. "This unambiguously identifies FRB 121102 as repeating," astronomers wrote of the discovery last year in Nature.
FRB 1211102's repetitive signal removed any doubt that astronomers are looking at a genuine astrophysical phenomena, rather than, say, random bursts of energy from the nearest microwave oven. Equally important, FRB 121102 proved that whatever is producing fast radio bursts — or at least, some of them — isn't being destroyed in the process.
Still, much more information was needed to figure out what's causing FRBs, starting with where in the universe they are coming from. Now, that mystery seems to have been solved for FRB 121102.
Prior to the new study, the patch of sky associated with FRB 121102's powerful outbursts was several arc minutes in diameter; wide enough to encompass hundreds of potential sources and many galaxies. To more precisely zero in on its location, Chatterjee and his co-authors turned to the National Radio Astronomy Observatory's Very Large Array (VLA). In 83 hours of observing time last year, they watched FBR 121102 fire off nine additional times, all at a consistent sky position. Follow-up observations with the Gemini North telescope in Hawaii revealed a very faint dwarf galaxy at precisely the location of the source.
A composite image of FRB 121102, located in a dim and distant host galaxy. Image:Gemini Observatory/AURA/NRC
More follow-up observations, with other telescope networks around the world including the European Very Long Baseline Interferometry (VLBI) Network, showed that the various FRB signals were occurring within 100 light years of each other. Astronomers also identified a fainter, continuous radio source, that also seems to be co-located.
"We think that the bursts and the continuous source are likely to be either the same object or that they are somehow physically associated with each other," Benito Marcote, a research at the of the Joint Institute for VLBI ERIC in the Netherlands, said in a statement.
So, now that we know where all the intergalactic chatter is coming from, can we say what's causing it? Not yet — but the location of FRB 121102 within a dim dwarf galaxy does imply one rather badass possibility: A magnetar. That's an insanely dense, rapidly rotating dead star with a magnetic field powerful enough to shred the entire cosmic neighbourhood to atoms.
"I favour the idea that they're related to magnetars," Williams said. He noted that dim dwarf galaxies, such as the one which birthed FRB 121102, also happen to be associated with another weird cosmic phenomenon — super-luminous supernovae. Nobody's really sure why the brightest stellar explosions are happening in the dimmest galaxies, but there's reason to suspect such environments might also be conducive to the formation of magnetars. Alternatively, the signal could be associated with an "active galactic nucleus", with radio jets coming from material surrounding the galaxy's supermassive black hole.
My personal pet theory is that the galaxy is dim because an advanced alien civilisation has built a Starkiller Base-esque contraption to systematically suck the life out of the stars, and that said alien death machine releases powerful energy bursts every time it knocks off another non-compliant planet. But according to scientists, I shouldn't get too attached to this idea.
"We've joked about spaceship battles and death stars blowing up, but we think we can explain it with ordinary physics," Chatterjee said.