Mystery burst from unusual pulsar or dying black hole in Galaxy
19 March 2014
Over the past few years, astronomers have been intrigued by a growing number of detections of very unusual bursts of radio waves of unknown origin. There are now six confirmed observations of these so-called "Fast Radio Bursts" (FRBs). These bursts are very bright and only last a few milliseconds. What makes them unusual is that each burst has only been detected once; they are unlike normal pulsars that emit repeated bursts of radio waves with clockwork precision. In addition, they are not associated with any known stars, galaxies or quasars.
A variety of explanations has been put forward to explain this strange phenomenon. FRBs may be the result of black holes or neutron stars annihilating one another. Or they could come from bizarre magnetic fields rearranging themselves near supernovae or highly magnetised stars. Another possibility is that they are from a rare type of pulsar. It is also thought that they may not even come from space but rather are produced by a strange weather phenomenon on Earth.
The main reason that we cannot identify their cause is that we have no measure of how far away they are. They could be anywhere from millions of light years to just tens of kiloparsecs distance. A detailed analysis of the signals suggests that the radio waves from the bursts traverse dense clouds of electrons before reaching our telescopes.
In a recent paper, CAASTRO members Dr Keith Bannister (CSIRO) and Dr Greg Madsen (University of Cambridge) have taken one step closer towards understanding FRBs. They analysed one burst that was observed at a low elevation above the horizon of the Galactic plane, near the Galactic plane. Using spectra from optical telescopes, they measured the amount of interstellar electrons in the direction of the burst and concluded that there is a 90% chance that the FRB resides inside our Galaxy. Its proximity rules out some of the explanations listed above. The researchers found that the only two viable interpretations are that this burst was either given off by an unusual pulsar or by an annihilating black hole in the Galaxy.
There currently are a number of vigorous, ongoing observational programs designed to find more FRBs for which we may be able to constrain the distance.
by G. Madsen