Gamma Ray Telescope Finds First "Invisible" Pulsar

October 16, 2008

A pulsar that had previously been invisible to orbiting and ground-based observatories has been discovered thanks to one of astronomy's newest pairs of "glasses," the Fermi Gamma-ray Space Telescope.

A pulsar is a type of neutron star, the small, dense remnant of a massive star that exploded as a supernova.

Unlike ordinary neutron stars, pulsars send out jets of radiation from their magnetic poles that sweep across Earth's line of sight as the star spins on its axis.

The newfound pulsar, which sits 4,600 light-years away in the constellation Cepheus, rotates at about a million miles an hour, and its beam of gamma rays reaches Earth about three times a second.

Fermi, a collaboration between NASA, the U.S. Department of Energy, and international partners, was launched in June to scan the skies for gamma rays, the most energetic wavelengths in the electromagnetic spectrum.

Pulsars have been spotted before based on radio waves and x-rays, but the new pulsar is the first object ever found solely based on gamma rays, according to Fermi scientists.

"We're learning that the Fermi telescope is the perfect instrument for finding young pulsars that were hidden from us before," said Alice Harding, a co-author on the study and a scientist at NASA's Goddard Space Flight Center in Maryland.

Harding said the mission could discover a new class of previously invisible pulsars, identify the mysterious sources of so-called gamma ray bursts, and expand estimates of the number of supernovae in our galaxy.

Higher Sensitivity

Radio beams from the first pulsar were discovered in 1968, and astronomers have counted 1,800 pulsars since then.

From 1991 through 2000, NASA's Energetic Gamma Ray Experiment Telescope (EGRET) cataloged hundreds of gamma ray sources, some of which turned out to be pulsars.

But many of EGRET's gamma ray sources remain unidentified, Harding said.

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