Jueves 6 de Noviembre de 2008, Ip nš 253

New kind of pulsar discovered
SYDNEY: About three times a second, a 10,000-year-old stellar corpse sweeps a beam of gamma-rays toward Earth. Discovered by NASA's Fermi Gamma-ray Space Telescope, this pulsar is the first known to blink in pure gamma rays.

"This is the first example of a new class of pulsars that will give us fundamental insights into how stars work," says Stanford University's Peter Michelson, principle investigator for the Large Area Telescope, one of the instruments aboard the orbiting observatory.

1,000 times the energy of our Sun

The new pulsar - detailed this week in the U.S. journal Science - lies within a supernova remnant known as CTA 1, located about 4,600 light-years away in the constellation Cepheus.

Its lighthouse-like beam sweeps Earth's way every 316.86 milliseconds. The pulsar, which formed in a supernova explosion about 10,000 years ago, emits 1,000 times the energy of our Sun.

Pulsars were first discovered in 1967 by a student radio astronomer. The radio pulses recorded were uncannily steady - so much so that some astronomers wondered if they were picking up signals from extraterrestrial civilisations.

The correct explanation was even stranger: Pulsars are spinning neutron stars packing the mass of the Sun into a sphere about 20 km across. Whirling around thousands of times each hour, they beam radio pulses into the cosmos in the style of a rapid-fire lighthouse.

Since then, about 1,800 pulsars have been discovered mainly via their radio emission. A fraction of pulsars go beyond radio; they also emit pulses of visible light, X-rays, and even high-energy gamma-rays.

Population of previously unsuspected pulsars

The Fermi observatory's discovery is different because it is a purely gamma-ray pulsar. The star is silent across parts of electromagnetic spectrum where pulsars are normally found and hints at a whole population of previously unsuspected pulsars waiting to be picked out of the heavens.

The pulsar in CTA 1 is not located at the centre of the supernova's expanding gaseous shell. Supernova explosions can be asymmetrical, often imparting a "kick" that sends the neutron star careening through space.

Based on the remnant's age and the pulsar's distance from its centre, astronomers believe the neutron star is moving at about a million miles per hour - a typical speed for neutron stars.

Fermi's Large Area Telescope scans the entire sky every three hours and detects photons with energies ranging from 20 million to more than 300 billion times the energy of visible light.

"The Large Area Telescope provides us with a unique probe of the galaxy's pulsar population, revealing objects we would not otherwise even know exist," said Fermi project scientist Steve Ritz of NASA's Goddard Space Flight Centre in Alabama, USA.

"This observation shows the power of the Large Area Telescope," Michelson adds. "It is so sensitive that we can now discover new types of objects just by observing their gamma-ray emissions."

  18/10/2008. Cosmos Magazine.