A Mysterious Rhythm Is Coming From Another Galaxy
Astronomers have been watching fast radio bursts for years, but nothing like this has ever been observed. The radio waves would arrive at random for about four days. Then nothing for the next 24 h. Then, another four days of haphazard pulses. Followed by another 12 days of silence.
For more than a year, the pattern—the well-defined swings from frenzy to calm and back again—persisted like clockwork.
In 2019, Dongzi Li, a doctorate student at the University of Toronto, began tracking these signals. CHIME, a Canadian-led project, studies astrophysical phenomena known as “fast radio bursts.” These invisible flashes, known as FRBs for short, come from all directions in space and reach Earth. They show up without warning and flash for a few milliseconds, matching the radiance of entire galaxies.
Astronomers don’t know what causes them; all they know is that they can travel for millions, if not billions, of years before reaching us. Astronomers were able to detect about 100 of them before they vanished during the past decade.
Li was monitoring FRBs at a radio telescope in British Columbia, tracking their arrival timings, when she discovered an unusual pattern from one FRB source—four days on, 12 days off. (This is, perhaps, the purest definition of radio silence.)
The FRB, known by the bar-code-esque designation 180916.J0158+65, is the first to show this kind of regular cadence. The source was tracked down to a spiral galaxy 500 million light-years away, where it is still burning.
The paper on this discovery, published earlier this month, marked the end of formal observations in February. Li has spent most of her days at home, rarely stepping beyond the walls of her little apartment in Bonn, Germany, like so many others this year, but the Canadian observatory continues to scan the skies, catching the fleeting FRBs as minute smudges of black against a plot of white noise. Li told me last week that she’s still checking—and the rhythm is still there.
The discovery is an intriguing addition to a growing inventory of knowledge in a field whose earliest evidence was almost dismissed as a fluke. The first FRB was discovered in 2007 as astronomers were seeking another astrophysical event in archival data from an Australian observatory. The signal was thought to be a telescope artifact, a light trick masquerading as a cosmic curiosity. Then, similar signals began to appear in observations at other telescopes.
Astronomers agreed that they had detected a real event, but they continued to believe that FRBs were one-offs. The flashes were so intense that whatever had caused them appeared unlikely to survive the cataclysm, even after traveling unfathomable distances in space. However, astronomers found a repeater, a source of FRBs capable of erupting repeatedly, sometimes numerous times in less than a minute.
Astronomers discovered a small, lively galaxy where new stars blink into existence more than 100 times quicker than in our own Milky Way when they traced a FRB to its host galaxy for the first time. So FRBs must come from these kinds of environments, they thought. However, astronomers discovered that some FRBs originated in larger, more mellow galaxies too though.
“It seems like every time the scientific community converges on a possibility of what FRBs might be, some other observation happens that throws all these speculations out the window,” Kaitlyn Shin, an astrophysics graduate student at MIT who worked on the discovery of the pattern-bearing FRB, told me. “Now all the other theories going forward have to find a way to account for
Not only from the FRB found by Shin and Li’s team, but another team revealed this month the discovery of a signal that pulses in a considerably longer pattern—a 157-day cycle with 90 days of bursts followed by 67 days of silence. Many other FRB sources may have distinct rhythms, but telescopes haven’t watched them long enough to discover them.
The nature of the objects that produce FRBs remains a mystery, but astronomers are collecting clues. The most important one to date appeared just two months ago—2020 has been a great year for FRBs, truly—when the observatory Li works with detected a FRB-like event inside our very own galaxy. The flash came from an astrophysical object called a magnetar, an ultramagnetic type of neutron star, the leftover core of an aging star.
For once, FRB astronomers were not completely surprised by a discovery in their field. Magnetars currently top the list of theories for the engines of these mysterious bursts.
Astronomers have now come up with a few potential explanations for the source of the FRB that jams to its own distinct tune. Perhaps the object is spinning and wobbling in such a way that its light points toward Earth just four out of every 16 days, which would appear to us as periodic bursts. Maybe it’s two objects—a neutron star orbiting another neutron star, or even a black hole in an orbit that squishes one star so hard that it flares as it swings around. Perhaps the source is near a cloud of interstellar gas that magnifies its radio emissions as it travels through, like a cosmic magnifying glass.
With so many possibilities, I couldn’t resist but questioning astronomers about the option on the edge of possibility, unlikely but also difficult to rule out: aliens. I admit that, despite knowing better, when I learned that astronomers had detected a distinct pattern emanating from outside the solar system, my mind jumped to Contact, the ’90s classic starring Jodie Foster as Ellie Arroway, a scientist obsessed with extraterrestrial life. When Li told her colleagues about the signals she observed, did they run from console to console in an operating room, scrambling to make the signal louder and clearer, as Arroway did?
No, because the story with FRBs—the story with the most mystifying astrophysical phenomena—is that it’s never aliens. However, those who are more qualified than I am considering that, perhaps, maybe, these could be alien signals: Avi Loeb, a Harvard scientist known for entertaining ET explanations, made a link this week between Li’s FRB and a planet in Proxima Centauri’s habitable zone, the star nearest to our sun. The planet takes 16 days to orbit its star, the same period observed in the FRB’s behavior, and Loeb suggested that perhaps the radio waves come from that planet, whose inhabitants have figured out how to harness and beam starlight, when their world turns our way.
But although the newly found FRB is indeed weird, it’s probably not a beacon from an advanced civilization. “This shares a lot of properties with other sorts of FRBs, which are not regular at all, so we don’t have any reason to believe that this one in particular is special,” Vikram Ravi, an astronomy professor who wasn’t involved in the research but who has discovered several FRBs, told me.
Moreover, Ravi expects a bit more from any aliens attempting to convey intergalactic greetings. “The signals are quite broadband, whereas it’s much more efficient to communicate in narrowband,” he said. “One would hope that if someone was communicating, it would be a bit more well defined.”
FRBs are a type of beacon, and astronomers have found more than is widely known. CHIME members reported in a document posted on the preprint repository arXiv.org in January that they had detected 700 FRBs in less than a year. When the catalog is formally published, it will exceed sevenfold the number of known signals. As these radio waves propagate through space, they pass through all kinds of matter, from the most luminous galaxies to nearly invisible wisps of cosmic dust, slowing down here and there. These interactions are encoded in radio waves, and scientists can detect them when the signals reach us.
Astronomers are particularly interested in studying the wispy material that lies between galaxies, because “we have no information other than what FRBs are beginning to give us,” says Shami Chatterjee, an astrophysicist at Cornell University who studies FRBs and was not involved in the new research. Astronomers require the help of these unusual signals, that they don’t understand fully, to see within this huge area.