Scientists search for source of mysterious cosmic radio bursts

The origins of cosmic "fast radio bursts," a phenomenon detected in 2007 and still a mystery to science, may be closer than we think, U.S. astrophysicists say. The characteristics of these cosmic chirps, lasting for only 0.001 second, had suggested the radio pulses came from galaxies billions of light-years away, but new research points to a much closer origin, they said -- flaring stars in the Milky Way. "We propose that fast radio bursts aren't as exotic as astronomers first thought," study lead author Avi Loeb of the Harvard-Smithsonian Center for Astrophysics said. Only six of these fast radio bursts -- brief and bright, packing a lot of energy into a short time -- have been discovered to date, all of them in archival data, the researchers said. Each was detected only once, making follow-up studies difficult. If their origin was billions of light years away, as first thought, they would have to come from extremely energetic events like the collapse of a neutron star into a black hole. However, Loeb and his colleagues reasoned, if the bursts came from a closer location, within the Milky Way galaxy, then they wouldn't require as much energy and could have a less exotic explanation. Stellar flares would fit the bill, they said, and two types of stars are known to create radio bursts: young, low mass stars and solar-mass "contact" binaries that orbit so close, they share their outer, gaseous envelopes. Loeb and his colleagues used telescopes to search the locations of three of the discovered fast radio bursts to look for such variable stars. They discovered a contact binary system in one location, and said statistics of stars across the observed field of view show there is less than a 5 percent chance the binary star is in the right place by coincidence. "Whenever we find a new class of sources, we debate whether they are close or far away," Loeb said. In the case of fast radio bursts, it seems, closer seems more likely than farther, the researchers said.