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Stars discovered flashing


By Christopher Williams, 15 Feb 2006

Astronomers at the the University of Manchester's Jodrell Bank Observatory have led an international team to discovering a new type of star, Rotating Radio Transients (RRATs). They are set to publish their findings in this week's edition of Nature.

A survey of the Milky Way for pulsars, using the Parkes Radio Telescope in Australia, revealed 11 sources of very short radio flashes, each around one hundredth of a second long and typically separated by three or four hours.

The time a RRAT may be visible to telescopes is tiny; a total of a tenth of a second per day. Once they realised they had something, a 14-strong team worked on the new phenomena for three years. Co-author of the paper Dr Maura McLaughlin explained: “It was difficult to believe that the flashes we saw came from outer space, because they looked very much like man-made interference.”

It is thought that RRATs, like pulsars, are a form of rotating neutron star.

Manchester professor Andrew Lyne told El Reg that while radio signals from pulsars (stellar lighthouses) have a regular period concurrent with their rotation, the RRATs at first seemed to pulse at random. Further investigation showed the long silences were always multiples of a shorter time, which the researchers believe is the period of the RRAT's rotation.

The period of more than half the known RRATs is over four seconds, Professor Lyne told us, much longer than for the vast majority of known pulsars. He said: “It's as if, following a flash, a RRAT has to gather its strength during perhaps a thousand rotations before it can do it again.”

However, the four second period is similar to that of Magnetars, which emit only X-rays or gamma radiation. The astronomers speculate that RRATs may represent an evolutionary stage of neutron stars to or from magnetars.

The Anglo-Australian team, which also included astronomers from the US, Canada and Italy, estimates that the new stellar class probably outnumber pulsars. Dr Richard Manchester of the Australia Telescope National Facility said: “Because of their ephemeral nature, RRATs are extremely difficult to find and so we believe that there are about four RRATs for every pulsar”. The number of 'normal' radio pulsars in our Galaxy is estimated to be about 100,000.

Professor Lyne framed the discovery: “In my 40-year career as an astronomer, I have had perhaps two other findings which approach this in interest.” ®

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