A Howling Cosmic Signal Came From a Faraway Galaxy

Astronomers get closer to understanding one of the most perplexing phenomena in the universe.

CSIRO / Alex Cherney

They never would have found it if Tony hadn’t gotten sick.

In September, astronomers were scanning the night sky with a radio telescope in Australia. They were looking for mysterious, powerful signals that originate well beyond the Milky Way and deep in space. Thousands of these signals, known as fast radio bursts, or FRBs, reach the planet each day, but they’re not easy to detect. The signals arrive without warning, flash for a few milliseconds, and then vanish.

The astronomers had anticipated catching at least a few bursts. Two weeks into the effort, they hadn’t detected anything, and it was time to turn the telescope over to other researchers. Disappointed, the team prepared to hand the reins back to Tony Maher, one of the telescope managers. But Maher, they were told, was out with a cold.

“So I said, ‘Why don’t I just take it for another 24 hours until Tony gets back?’” says Keith Bannister, a research engineer at the Australia Telescope National Facility who led the team. “And then 2 a.m. that morning, all hell broke loose.”

They got one.

The discovery, published today in Science, brings the tally of known FRBs to more than 80. A second team is working on a similar discovery, too—an enticing prospect for a burgeoning field with more questions than answers. Despite the growing catalog, astronomers are missing a crucial piece of information: what, exactly, produces these things.

The first known FRBs, detected about a decade ago, were so unusual that astronomers suspected the signals were noise from telescope instruments. By the time the bursts approach Earth, they have traveled for billions of years across the cosmic expanse, and yet they arrive not as faint whispers, but as screeching howls. The energy in these momentary bursts can outshine the entire sun. A leading theory on their origins suggests that the pulses erupt from magnetars, star remnants with tremendously powerful magnetic fields.

The astronomers were thrilled about detecting another FRB, a rare enough triumph. But even more exciting was what they were able to discover about its origins.

The telescope they used is actually a collection of 36 individual dish-shaped antennae spread out across a patch of desert in Australia. The antennae jut out of the scarlet-colored terrain like mushrooms, rotating their tops toward different parts of the sky. When an FRB washes over Earth, the signal hits every dish at a slightly different time. “We can measure those times very accurately, down to a fraction of a billionth of a second,” Bannister says. His team stitched these measurements together to triangulate the source of the burst.

With the cosmic coordinates in hand, the researchers wrangled other telescopes around the world to check out that spot. Sure enough, they found something: a galaxy, slightly smaller than our own, about 4 billion light-years away. This particular FRB, named 180924, for the date of its discovery, erupted from this distant place long, long before a curious civilization built the technology to find it.

Bannister explains the precision of the discovery this way: “It’s like looking at the Earth from the moon and not only knowing what house a person lived in, but what chair they were sitting in at the dining-room table.”

This is only the second time astronomers have managed to pinpoint the source of one of these signals. The other FRB, known as 121102, is regarded as quite special in the field; it’s the rare signal that has been known to appear more than once, always from the same bit of sky—sometimes several times in less than a minute. Astronomers traced its source to a galaxy about 3 billion light-years away last year.

Most FRBs, though, are one-off events, and identifying their source right away is a significant achievement. “This is a very big leap,” says Sarah Burke Spolaor, an astronomer at West Virginia University who studies FRBs and was not involved in the research.

The finding stands to shake up current theories. The earlier, 121102 burst originated in a small galaxy that seemed to be churning out stars. Massive stars exploded in dazzling supernovas, a process that gave rise to new stars and left behind magnetars. That kind of environment seemed like the perfect place to manufacture energetic mysteries such as FRBs. But the home galaxy of 180924 is larger and sleepier. “It’s not really doing that much, and yet it can produce FRBs,” Bannister says. The bursts might be coming from two different types of cosmic objects, each cataclysmic enough to send radio waves streaking across the universe.

Even as the most fundamental properties of FRBs remain hidden, more detections could bring astronomers closer to answering an entirely different cosmic conundrum: what the universe is made of. To telescopes, FRBs appear smudged across a range of frequencies, a distortion that suggests something slowed them down between galaxies. They seem to bear the marks of intergalactic matter, something astronomers know little about.

“The interstellar medium between stars in our galaxy is a better vacuum than the vacuums we have in labs, and the intergalactic medium is orders of magnitude emptier than even that,” says Shami Chatterjee, an astrophysicist at Cornell University who studies FRBs and was not involved in the new research. “But there is some material there, and there’s so much intergalactic space that it adds up.”

It adds up quite a bit: Even with all the planets, stars, and galaxies, most of the composition of the universe remains unknown. FRBs could serve as beacons, studded with clues, to illuminate the depths.