venerdì 11 luglio 2014

Aricebo Observatory Picks Up Mysterious Radio Burst From Beyond The Milky Way

John P. Millis, Ph.D.
Over the last few years the Parkes radio telescope in Australia has detected a handful of short radio bursts emanating from deep space. This was an amazing discovery, except for the fact that no other radio facilities had seen such pulses, leading some to suggest that the instrument was detecting terrestrial signals. But now, the Arecibo radio telescope has made a similar detection that has the astronomical community talking.
The largest and most sensitive single dish radio telescope in the world, the Arecibo telescope is built into 20 acres of Puerto Rican countryside.
“Our result is important because it eliminates any doubt that these radio bursts are truly of cosmic origin,” said Victoria Kaspi, an astrophysics professor at McGill University in Montreal and Principal Investigator on the pulsar-survey project that detected the event. “The radio waves show every sign of having come from far outside our galaxy – a really exciting prospect.”
However, questions remain as to the actual origin of these radio bursts. Some astrophysicists believe that the source could be mergers or eruptions from exotic objects, such as black holes or pulsars. “Another possibility is that they are bursts much brighter than the giant pulses seen from some pulsars,” notes James Cordes, a professor of astronomy at Cornell University and co-author of the new study.
Only a few of these events have ever been definitively detected, and only lasting a tiny fraction of a second; however, astronomers estimate that these bursts occur about 10,000 times per day. The reason that they have not been detected more frequently is that the telescope can only cover a small part of the sky at once, so there are limited chances that the telescope is pointing at just the right position at just the right time.
Also, the short bursts are difficult to isolate from the background, because of their short time interval. But the team of scientists was lucky in that they were searching specifically for high frequency events associated with pulsars and gravitational wave events.
“The brightness and duration of this event, and the inferred rate at which these bursts occur, are all consistent with the properties of the bursts previously detected by the Parkes telescope in Australia,” said Laura Spitler, now a postdoctoral researcher at the Max Planck Institute for Radio Astronomy in Bonn, Germany.
Astronomers are certain that the bursts originate beyond the Milky Way because of the radio dispersion measurements. When radio waves travel through space they interact with free electrons, causing them to slow inversely proportional to their frequency. The observed dispersion is three times the maximum that would be expected if the radio signal originated from our own galaxy.
Attention is now being turned to observing large portions of the sky at once to detect more of these events, with the hopes of determining their exact origin. New instruments currently being developed will also aid in this search by covering more of the sky, increasing the chances of detection.
Findings from this study were published in the July 10 issue of The Astrophysics Journal.


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