Swinburne University of Technology - Melbourne Australia

Giant energy burst reveals new cosmic horizons

Story by Julian Cribb

A cryptic blast of radio energy from deep space lasting just thousandths of a second has astonished astronomers - and, tantalisingly, may offer a new way to observe how the universe unfolded.

A team of researchers from Swinburne University of Technology and West Virginia University (WVU) is racing to find out more about the mysterious cosmological phenomenon, discovered by chance when an undergraduate student was reviewing results from a pulsar survey by Australia's Parkes Radio Telescope.

So powerful was the burst it had saturated the primary sensor tuned to it and had been excluded by the software that analysed the results as an improbability, recounts team member Professor Matthew Bailes, director of Swinburne's Centre for Astrophysics and Supercomputing.

Although it lasted only five milliseconds, the radio hyperburst outshone by many thousands of times the normal signals emitted by pulsars, which are the spinning embers of collapsed giant stars. Intriguingly too, it seemed to originate from a point outside the known local cluster of galaxies.

"It was just booming in. It was very, very bright," Professor Bailes says. "Normally, radio sources in our own galaxy look bright because they are so close, whereas those that are far away are very faint. This burst appears to have originated in the distant universe and yet was still extremely bright, suggesting it may have been produced by a rare, brief, but very violent event such as the collision of two neutron stars, the moment of crisis in a supernova, or the evaporation or formation of a black hole."

The discovery has galvanised the international cosmological community, less for the fact that it reveals a previously unseen event but more for potentially being a new method for observing the evolution of the universe itself.

The event was first noted by David Narkevic, a student of team leader Professor Duncan Lorimer, of WVU, among data recorded in a Parkes survey carried out seven years ago. The receiver that picked it up had 13 detectors, two of which recorded an extreme event while the other 11 showed nothing. "This was a bit of a mystery," Professor Bailes says, "so we ran the data through the Swinburne supercomputer and found the signal was so powerful that the original software had automatically clipped it out."

Most pulsars emit a signal of about one milliJansky. This signal was 30 Janskys - or 30,000 times more powerful. It had simply overwhelmed the primary receiver and fooled the analytic software into thinking it must be interference.

Despite the saturation level of the signal, the team was able to measure its flux - to see the signal brightening and fading over a period of about a third of a second. From this they have deduced the signal came from far away - perhaps a billion light years - and from a tiny source that may be no larger than 1500 kilometres across, suggesting a small but super-violent event, such as a pulsar collision or black hole formation as the primary cause.

However, as with the discovery of radio astronomy itself, or the more recent development of gamma ray observations, each new form of signal detected from the heavens offers humanity a fresh window for viewing the cosmos. In the case of these brief radio hyperbursts, the team considers that, although rare, such events may still occur from time to time and if we can pinpoint the source of one and measure its redshift, or distance from Earth, it will give us a new means to study the universe's evolution.

"Radio waves are slightly delayed by all the electrons they encounter on their way to us. If we knew where they originated and how far away they were, we could estimate the density of all the matter - including that which we cannot see - that lies between us and the source," Professor Bailes explains. "This would enable us to calculate the mass density of the universe at a particular time, and that is exciting. It would really tie down all the models we have for the evolution and expansion of the universe itself.

"Unfortunately, this particular hyperburst has faded, and we have not been able to pinpoint the galaxy or event it came from."

However, a renewed sense of urgency has now gripped the Swinburne and WVU team since its original discovery. The hunt is on to pinpoint other huge bursts of radio emissions and, if possible, to correlate them with a particular event in a galaxy lying at a known distance from us. The team is already churning radio data collected over recent years through the Swinburne supercomputer, trying to pick up similar events.

The next stage in the research will be to put as many radio and optical telescopes as possible around the world on standby, ready to follow up when a hyperburst is next detected and report the redshift of its source, Professor Bailes says. The proposed next-generation radio detector, the Square Kilometre Array (should Australia win the bid to build it), and Gravity Wave Observatory could also both be involved in the hunt.