For years, astronomers have puzzled over “fast radio bursts” (FRBs), mysterious cosmic beats that may come from pulsars. Now, for the first time, researchers have pinpointed the location of one such burst — and the discovery hints at an even more epic origin story.
FRBs are extremely energetic pulses that last only a few milliseconds and originate from seemingly random locations in the sky. To date, we’ve observed just 17 of them, although astronomers suspect there could be thousands flitting through our fields of view each day. There’s no generally accepted explanation for how they’re created, but theories abound: pulsars, collapsing neutron stars, evaporating black holes, and finally — humanity’s favourite explanation for strange cosmic chatter — alien beacons.
Although pulsars are the leading hypothesis among astronomers, and aliens are obviously our preferred choice, we won’t know which of these explanations makes sense until we learn more about the signals, including where in space they originate.
The good news is that we’re finally starting to figure it out. As reported today in Nature, astronomers working at the Parkes radio telescope in Australia have pinpointed the location of FRB 150418, which released two days worth of our Sun’s energy in a fraction of a second.
While most FRBs have been discovered post facto in archival data, FRB 150418 was detected seconds after it reached the Parkes telescope on April 18th, 2015. This allowed astronomers to quickly mobilise other telescopes, and observe the same patch of sky across the electromagnetic spectrum.
Essentially, researchers followed a breadcrumb trail of lightwaves to the FRB’s origin — an elliptical galaxy some 6 billion light years distant.
The characteristic sweeping signal of an FRB is shown in the closest inset—a so-called ‘waterfall plot’. Using multiple telescopes, astronomers pinpointed the location of this FRB to an elliptical galaxy six billion light years away. Via David Kaplan & Evan Keane.
And that location tells us a lot about the signal’s likely origin. For one, the galaxy FRB 150418 comes from is very old, which allows us to rule out the bright stellar beacons known as pulsars.
“Something like a pulsar doesn’t live that long, so when you see it, it is young, and not that long since it was born,” lead study author Evan Keane told Gizmodo in an email. “So as there is low or no star formation happening in the galaxy now it means the source is probably not from a young stellar population.”
Instead, Keane said, the radio burst probably emanated from the collision of two stars, possibly, two neutron stars. Other evidence, including the afterglow of the elliptical galaxy, supports the idea that we’re listening to the cosmic scream of two massive objects smashing into each other.
A year ago, that might have been the end of the story. But the collision of two neutron stars produces something else: gravitational waves. Now that the Laser Interferometer Gravitational Wave Observatory (LIGO) has confirmed the existence of Einstein’s spacetime ripples, we can start using gravitational waves to probe all sorts of cosmic mysteries, including fast radio bursts.
“The next big thing for FRB hunters, and gravitational wave hunters, is to find something emitting in both domains,” Keane said. “With multi-messenger work like that we can do amazing physics.”
Sit tight, Earthlings: the answers are coming.