Cosmic Space

Fast radio bursts linked to a prime suspect

For years, astronomers have puzzled over the origins of phenomena known as fast radio bursts — cosmic emissions that last only a fraction of a second but blast out more than 100 million times more power than our sun. Some even wondered whether the bursts, known as FRBs, might serve as signals from extraterrestrial civilizations.

Now they’ve tracked down the source of the first fast radio burst detected in our own Milky Way galaxy — and it’s not aliens. Instead, it’s a magnetar, a type of neutron star with a powerful magnetic field.

Scientists have long suspected that fast radio bursts had something to do with magnetars. But the newly reported case, described in three studies published today by the journal Nature, serves as the astronomical equivalent of a smoking gun.

“There’s this great mystery as to what would produce these great outbursts of energy, which until now we’ve seen coming from halfway across the universe,” Kiyoshi Masui, a physicist at the Massachusetts Institute of Technology, said today in a news release. “This is the first time we’ve been able to tie one of these exotic fast radio bursts to a single astrophysical object.”

Masui is part of the team that picked up the first clues to the source, a magnetar 30,000 light-years from Earth that’s known as SGR 1935+2154. The team includes researchers from MIT, the University of British Columbia, McGill University, the University of Toronto and the Perimeter Institute for Theoretical Physics.

They made use of a radio telescope array called the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, which began science operations in 2018 at the Dominion Radio Astrophysical Observatory in British Columbia’s Okanagan Valley.

In April, astronomers detected bursts of X-ray and gamma-ray activity from SGR 1935 — which led the CHIME team to turn their attention to that part of the sky, around the center of the Milky Way. Shortly after an X-ray burst on April 28, CHIME registered two sharp peaks in radio emissions, within a few milliseconds of each other.

That fit the pattern for a fast radio burst, emanating from a point in the vicinity of SGR 1935. “If it was coming from any other object close to the magnetar, it would be a very big coincidence,” Masui said.

The source was near the edge of CHIME’s field of view, which made it difficult to determine the radio burst’s brightness. So the team put out the word for other astronomers to check their records.

By a stroke of luck, another radio astronomy project —  known as the Survey for Transient Astronomical Radio Emission 2, or STARE2 — had a wide-field view of the same blast.

“When I saw the data, I was basically paralyzed,” Caltech graduate student Christopher Bochenek said in a news release. “At the radio frequencies we observe with STARE2, the signal was much stronger than what CHIME reported. We had caught the FRB head-on.”

STARE2 isn’t your typical radio telescope array: The heart of the Caltech-led, NASA-funded project is a handmade radio receiver that’s about the size of a large bucket. “It’s a piece of 6-inch metal pipe with two literal cake pans around it,” Bochenek told The Associated Press.

Three of the receivers are placed at widely separated locations in California and Utah, which makes it possible to triangulate on the source of cosmic radio emissions. They’re not as sensitive as the more traditional big-dish telescopes, but they can take in the whole sky.

The readings from STARE2, combined with data from other instruments, suggested that the April 28 burst was 3,000 times brighter than any previously observed magnetar radio signal.

Among the other instruments participating in the observational campaign was China’s Five-Hundred-Meter Aperture Spherical Radio Telescope, also known as FAST. Astronomers on the FAST team missed out on detecting FRB 200428, but they kept an eye on SGR 1935 as it emitted a series of 29 gamma-ray bursts. None of those bursts coincided with a blast of high-energy radio waves.

“The weak correlation could be explained by special geometry and/or limited bandwidth of FRBs,” study co-author Zhang Bing of the University of Nevada at Las Vegas said in a news release. “The observations of SGR J1935 start to reveal the magnetar origin of FRBs, although other possibilities still exist.”

Astrophysicists haven’t yet figured out the mechanism for producing fast radio bursts, but one hypothesis is that they can occur when a magnetar throws off a flare of charged particles that interact with debris surrounding the star. The resulting shock wave could set electrons gyrating wildly, throwing off radio waves as well as X-rays.

To unravel that part of the mystery, the CHIME team and other astronomers are keeping a close watch on SGR 1935.

“We’ve got our eyes open for other magnetars,” Masui said, “but the big thing now is to study this one source and really drill down to see what it tells us about how FRBs are made.”

The CHIME/FRB Collaboration’s study, described in a Nature paper titled “A Bright Millisecond-Duration Radio Burst From a Galactic Magnetar,” was funded by the Canada Foundation for Innovation and other supporting institutions. The second Nature study, “A Fast Radio Burst Associated With a Galactic Magnetar” counts Bochenek as well as V. Ravi, K.V. Belov, G. Hallinan, J. Kocz, S.R. Kulkarni and D.L. McKenna among its authors. Zhang is among 48 authors of the third Nature paper, titled “No Pulsed Radio Emission During a Bursting Phase of a Galactic Magnetar.”


Search for fast radio bursts enters a new era

CHIME antenna
One of the radio antennas of the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, spreads out beneath the night sky near Penticton, B.C. (CHIME Photo)

A new radio telescope in British Columbia’s Okanagan Valley has detected 13 new sources of mysterious extragalactic phenomena known as fast radio bursts, including the second known source of repeated bursts.

And the experiment is just barely getting started.

The Canadian Hydrogen Intensity Mapping Experiment, or CHIME, picked up the radio signatures of the bursts over the course of three weeks in July and August, while the telescope was in its pre-commissioning phase and running at only a fraction of its design capacity.

Fast radio bursts, also known as FRBs, are powerful spikes of radio emissions that emanate from galaxies beyond our own Milky Way and last for mere milliseconds. Only 60 FRB sources have been detected, including the 13 announced today.

“Their origin is still unknown,” said the University of British Columbia astronomer Deborah Good, one of the co-authors of two papers about the detections published today by the journal Nature.

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AI helps SETI sleuths find more radio bursts

AI seeking ET
Researchers used artificial intelligence to search through data from a radio source, capturing many more fast radio bursts than humans could. (Breakthrough Listen Illustration / Danielle Futselaar)

Researchers at Breakthrough Listen, a multimillion-dollar campaign to seek out signals from alien civilizations, still don’t know exactly what’s causing repeated bursts of radio waves from an distant galaxy — but thanks to artificial intelligence, they’re keeping closer tabs on the source, whatever it turns out to be.

A team led by Gerry Zhang, a graduate student at the University of California at Berkeley, developed a new type of machine-learning algorithm to comb through data collected a year ago during an observing campaign that used the Green Bank Telescope in West Virginia.

The campaign focused on a radio source known as FRB 121102, located in a dwarf galaxy sitting 3 billion light-years away in the constellation Auriga. Astronomers have observed plenty of fast radio bursts over the past decade, each lasting only a few milliseconds. Only FRB 121102 has been found to send out repeated bursts, however.

A number of theories have been proposed to explain the bursts, ranging from interactions involving magnetized neutron stars and black holes to deliberate signaling by advanced civilizations.

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Alien hunters track strange radio bursts

Green Bank Telescope
Intriguing signals have been picked up via West Virginia’s Green Bank Telescope. (NRAO Photo)

Breakthrough Listen, a $100 million initiative aimed at stepping up the search for alien signals, says it’s picked up an intriguing series of 15 fast radio bursts emanating from a dwarf galaxy 3 billion light-years away.

It’s way too early to claim that the signals from the galaxy, which hosts a radio source known as FRB 121102, constitute the kind of evidence sought for decades by researchers specializing in the search for extraterrestrial intelligence, or SETI.

But Breakthrough Listen’s researchers say that possibility can’t yet be ruled out.

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