Space

Strange Radio Signals Mystify Astronomers

July 11, 2014 | by Stephen Luntz

Photo credit: Rogelio Bernal Andreo (DeepSkyColors.com). The area of the sky in which the Arecibo Fast Radio Burst was detected is circled. The nearby supernova remnant and star formation region are coincidental, with the burst coming from much greater distances

One of the world's great radio telescopes isn't hearing voices – for the first time another giant dish has picked up one of the mysterious “fast radio bursts” (FRBs) that have been puzzling astronomers at the Parkes Radio Telescope. The find confirms these bursts indeed come from outer space, but beyond that their source is still wide open.

Last year the astronomers reported four bursts picked up by the celebrated Australian telescope. As each FRB lasted around a millisecond there was no time to have other telescopes check the same location, and the fact that no other telescope had picked up anything similar raised the possibility that something local was interfering with the Parkes telescope.

Now, however The Astrophysical Journal reports that the 305m Arecibo Telescope has picked up a similar burst while searching for pulsars. The burst occurred in 2012, but not noticed at the time. “FRB 121102's brightness, duration, and the inferred event rate are all consistent with the properties of the previously detected Parkes bursts,” the authors report.

"Our result is important because it eliminates any doubt that these radio bursts are truly of cosmic origin," says McGill's Professor Victoria Kaspi.

Despite the short nature of the FRBs, some things about their nature have been inferred. Those detected at Parkes were all more than 40° from the Galactic Plane, suggesting they almost certainly come from outside the Milky Way. Moreover, different frequencies arrive at slightly different times. This suggests the radio waves have traveled extensively through an ionized medium, in which any electromagnetic radiation will be slowed down. Shorter wavelengths are slowed by more, just as blue light is delayed more in glass, and therefore more bent by a prism than longer wavelength red.

The Parkes FRBs were estimated as having come from distances as great as 9 billion light years, suggesting a very powerful source. Theories so far include evaporating black holes, magnetar flares and the mergers of neutron stars. However, the FRBs do not seem to be associated with the more famous Gamma Ray Bursts, for which the same explanations have been proposed.

With only a handful of observations from all the world's telescopes it might be expected that FRBs are very rare, but by calculating the area of the sky studied with sufficient sensitivity to pick such events up, the authors conclude 10,000 occur each day.