Astronomers Find Mysterious Radio Burst
A visible-light image of the Small Magellanic Cloud, combined with radio observation data (contoured lines). The blue circle marks where a strange 5-millisecond radio burst originated.
Credit: Lorimer et al., NRAO, AUI, NSF

A new and intense type of radio burst has been discovered in archived views of the cosmos, astronomers revealed today.

The single, short-lived blast of radio waves likely occurred some 3 billion light-years from Earth, and it may signal a cosmic car crash of two neutron stars, the death throes of a black hole—or something else.

"This is something that's completely unprecedented," said Duncan Lorimer, an astrophysicist at West Virginia University in Morgantown and the National Radio Astronomy Observatory who led the discovery-making team. He noted that radio-emitting pulsars send out similar emissions, but repeat them every few hours.

"We're confused and excited, but it could open up a whole new research field," Lorimer told of the 5-millisecond blip on the cosmic radar screen. "If we really go after these things, we expect to find out that a couple hundred of them occur each day."

The discovery is detailed in the Sept. 27 issue of the online journal Science Express.

Blast from beyond

The previously undetected radio burst was found in data from a 2001 radio survey of the Small Magellanic Cloud, a nearby dwarf galaxy. Based on its location, however, Lorimer said the burst almost certainly did not come from the galaxy.

Lorimer said the emission's offset location and wide dispersion made it "completely inconsistent" with that of a nearby object, whether in our own galaxy or the Small Magellanic Cloud.

Astronomers originally created the 480-hour-long observation over 20 days to look for repetitive radio emissions from pulsars, which are thought to be fast-rotating neutron stars, but the event remained hidden in the data because no one had set out to find single bursts.

"We've looked at it for about 90 hours, and it definitely seems to be a singular event," he said.

Blip on the screen

Lorimer cautioned that it's impossible to say for certain what the radio burst might indicate at this point, as it is the only one that has been detected so far.

"We're keeping very open minds about this thing," Lorimer said, adding that their uncertainty stems from the inability to pinpoint it to a galaxy or other celestial object that could reveal some clues to its identity. "We're putting a lot of effort into poring through other radio data to find more of these things."

So far, the search has left the researchers empty-handed, but it may be an issue of sensitivity. Lorimer emphasized that the records are several years old and few radio observatories have the sensitivity to detect such short bursts.

"Based on the area we looked at, we think this type of burst may occur at a rate of a couple hundred each day," Lorimer said. He thinks that whole-sky surveys using next-generation radio observatories would be needed to detect most of them.

Leg-up for LIGO?

If the bursts are as frequent as Lorimer's team thinks, and they indicate the death of black holes or two super-dense neutron stars violently smacking together, a step toward closure of the universe's great mystery of gravity may soon come.

The dramatic cosmic events are predicted to let loose gravity waves that Einstein's theory of relativity predicts, but the phenomenon has never been directly observed. LIGO—the Laser Interferometer Gravitational Wave Observatory based in both Louisiana and Washington state—has been searching for such waves since it went online in 2002.

Lorimer thinks the singular radio bursts could give gravitational wave researchers some help filtering LIGO data, which contains noise from Earth-based activities such as logging and highway traffic.

"This finding is definitely something LIGO will be interested in," said Xavier Siemens, a gravitational theorist at the University of Wisconsin Milwaukee and LIGO who was not involved in Lorimer's study. He said the burst occurred about one year before the observatory began its scientific observations, so researchers can't look for it in old data.

"It's an exciting result, and if they eventually find that the bursts occur at rates as high as they expect, then it's even more exciting to us," Siemens said, "because we should be able to measure them at LIGO."