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Repetitive patterns found in mysterious cosmic bursts of radio waves

With the help of the world's largest radio telescope, the Arecibo Observatory, astronomers have, for the first time, detected repeated bursts of radio waves from a source well beyond the edge of our Milky Way galaxy. The origin of these "fast radio bursts" (FRBs), lasting only one thousandths of a second, is a decade-old puzzle in astronomy.

Prior to this discovery, reported in Nature , all previously detected FRBs have appeared to be one-off events. Despite extensive efforts, astronomers until now have failed to detect repeated bursts. "Our discovery shows that at least some FRBs must originate from something like a super-high-powered rotating neutron star that can regularly emit extremely bright pulses," says Laura Spitler, postdoc at the Max Planck Institute for Radio Astronomy and lead author of the paper. "This is a crucial step in determining what causes these bursts, which appear to originate in galaxies far beyond our Milky Way."

"Without the Arecibo Observatory, most, if not all, of these events would have gone unseen," according to Andrew Seymour, a postdoc at the Arecibo Observatory in Puerto Rico. The Observatory houses the world's largest and most sensitive dish single dish telescope- 1000 feet in diameter.

Multiple events from the same location were confirmed by McGill University graduate student Paul Scholz with results from observations performed at Arecibo Observatory. The new data, gathered in May and June and run through a supercomputer in Montreal, Canada, showed bursts with properties consistent with a FRB detected two years earlier (in 2013) by the same team.

The repeat signals were surprising - and "very exciting," Scholz says. "I knew immediately that the discovery would be extremely important in the study of FRBs." As his office mates gathered around his computer screen, Scholz pored over the remaining output from specialized software used to search for pulsars and radio bursts. He found that there were a total of ten new bursts.

Scientists believe that these and other FRBs originate from distant galaxies, based on the measurement of an effect known as plasma dispersion. Pulses that travel through the cosmos are distinguished from man-made interference by the influence of interstellar electrons, which cause radio waves to travel more slowly at lower frequencies. The ten newly detected bursts, like the one discovered in 2013, have three times the maximum dispersion measure that would be expected from a source within the galaxy.

In future research, the team hopes to identify the galaxy where these radio bursts originated. Using a technique called interferometry, performed with radio telescopes spread over large geographical distances, astronomers will be able to achieve the needed resolution. "Once we have a precise location, we will be able to compare observations from optical and X-ray telescopes and see if there is a galaxy at that location; this will be the next breakthrough," says Jason Hessels, associate professor at the University of Amsterdam and ASTRON, the Netherlands Institute for Radio Astronomy as well as corresponding author of the Nature paper. "Finding the host galaxy of this source is the next step in understanding its properties", he adds.

"Now with multiple events from the same location, we can start to zero in on the actual cause and we won't be forced to speculate much longer", explained Seymour.

The Arecibo Observatory is operated by SRI International in partnership with Ana G. Méndez University System-Universidad Metropolitana and Universities Space Research Administration (USRA) under a cooperative agreement with the National Science Foundation. The research was supported by grants from the European Research Council, the National Science and Engineering Council of Canada, and the American National Science Foundation.

From space, a sequence of millisecond-duration radio flashes

Image: The 305-m Arecibo telescope and its suspended support platform of radio receivers is shown amid a starry night. From space, a sequence of millisecond-duration radio flashes are racing towards the dish, where they will be reflected and detected by the radio receivers. Such radio signals are called fast radio bursts, and Arecibo is the first telescope to see repeat bursts from the same source. Figure Credit: Danielle Futselaar

About USRA

Universities Space Research Association is an independent, nonprofit research corporation where the combined efforts of in-house talent and university-based expertise merge to advance space science and technology. USRA works across disciplines including biomedicine, planetary science, astrophysics, and engineering and integrates those competencies into applications ranging from fundamental research to facility management and operations. USRA engages the creativity and authoritative expertise of the research community to develop and deliver sophisticated, forward-looking solutions to Federal agencies and other government sponsors.