In 2007, astrophysicists at West Virginia University stumbled upon something strange as they reviewed archival data at the Parkes radio telescope in Australia. They found the telescope had detected a powerful flash of radio waves that lasted less than five milliseconds. The signal appeared smeared across a range of frequencies, a sign that the burst had traveled a huge distance—about 3 billion light-years—to Earth. It must have originated from outside the Milky Way, in a distant corner of the universe.
“We’re confused and excited, but it could open up a whole new research field,” Duncan Lorimer, the astrophysicist who co-discovered the signal, said back then. The signal was dubbed a fast radio burst, or FRB.
Lorimer’s prediction was correct. Since that first discovery, scientists have detected about 30 FRBs, coming from all kinds of directions, mined from old data and observed in real time. A decade of careful research has proven these mysterious, high-energy pulses to be real astrophysical phenomena from beyond the galaxy, and not just instrument noise from telescopes, as many first thought. Scientists estimate the bursts occur about 10,000 times a day across the entire sky.
All known FRBs are tantalizing targets, but there’s one in particular astrophysicists love to study: FRB 121102, first detected in 2012. After that, FRB 121102 flashed again—and then again and again and again, eventually racking up more than 150 detected bursts. Before its detection, FRBs were assumed to be one-time events, the products of cataclysmic eruptions or collisions that destroyed their progenitors. The repeating nature of FRB 121102 changed all that. Scientists went after it with hours of observations. Last January, they pinpointed its location to a small galaxy about 2.5 billion light-years from Earth.
“This source has really been a gold mine,” said Jason Hessels, an astronomer at the University of Amsterdam and ASTRON, the Netherlands Institute for Radio Astronomy.
Now, another gem about FRB 121102 has been unearthed. On Wednesday, Hessels and other members of an international team of astronomers announced new results from their observations of the FRB by two of the most powerful radio telescopes in the world, the Arecibo Observatory in Puerto Rico and the Green Bank Telescope in West Virginia. The GBT studied the source in high radio frequencies using a powerful backend built by Breakthrough Listen, a project to fund efforts in the search for extraterrestrial life. Their findings are published in Nature.
The team detected and studied 16 pulses from FRB 121102. They found the radio waves were highly polarized, a property that describes the nature of the vibrations as they travel through space. When they arrived at Earth, the polarized radio waves exhibited something known as the Faraday rotation, a phenomenon in which waves become twisted as they propagate through strong magnetic fields.
“When [radio waves] pass through material, they get distorted in complicated ways,” Hessels said. “Looking at all the ways the radio waves have been distorted can tell us about the material the radio waves passed through.”
The more powerful the magnetic field is, the more severe the twisting becomes as radio waves move through it. And the twisting in this case was dramatic. Scientists have only seen an effect of this magnitude in one other place—at the center of our galaxy, where a supermassive black hole lurks. The researchers say the extreme effect suggests FRB 121102 originates from a similar, extreme environment, made up of dense plasma, which is hot, ionized gas.
The findings support the leading hypotheses for the origins of FRBs, like black holes, the light-devouring beasts of the cosmos, and neutron stars, the leftover cores of stars that died in spectacular explosions called supernovae. Both kinds of objects are surrounded by extreme environments with strong magnetic fields and high temperatures.
The mystery of FRBs is far from solved. Despite this glimpse into one burst’s potential environment, scientists still don’t know exactly where these pulses come from, how they erupt, and why. But every data point is crucial in a burgeoning research area. “Because the field is so new, because we know so little about the phenomenon, almost everything we see is an important sign and an important step forward,” Hessels said.
It’s unclear whether FRB 121102 is a good representation of the population of known FRBs. Because it’s the only pulse of the batch to repeat, 121102 may have a different origin story than the others. This burst came came from a dwarf galaxy, but that doesn’t mean that all FRBs come from dwarf galaxies, for example. “At the moment, every FRB is atypical,” said Andrew Siemion, the director of the Berkeley SETI Research Center and one of the paper’s authors.
Scientists hope to determine the locations of other FRBs—and not just for the sake of learning more about these bizarre pulses. The study of FRBs has important implications for cosmology, the study of the origins and evolution of the universe. While fleeting, FRBs are very bright events that can, for a very short time, highlight hidden parts of the cosmos, like the material that lies between galaxies
“FRBs are exciting because they’re explosive and that’s all great, but if you think about it, that’s not really the reason we’re excited about them,” said Sarah Burke-Spolaor, an astronomer at West Virginia University who studies FRBs. “The ultimate reason we want to detect and study them is they’re so good at telling us about the fluff between them and us. Any time they propagate and travel through the fluff between galaxies, that fluff affects the radio bursts, and we can detect the effect down here.”
Perhaps someday, FRBs could serve a similar purpose as other illuminating astrophysical objects, like Type Ia supernovae, which have helped astronomers estimate for the rate of the expansion of the universe. Scientists study the brightness of these exploding stars to calculate the distances of other galaxies, and then use that information to measure the expansion of the cosmos.
Until then, scientists remain, as Lorimer put it a decade ago, “confused and excited.” Members of the FRB community say it has certainly been on a roll of important findings in the last few years, but the discoveries have only raised more questions.
“The more information you get, the more complex the story becomes,” Burke-Spolaor said.
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