Article Posted on : - Oct 10, 2011

An artist's conception shows the Crab Nebula pulsar. Photo: David A. Aguilar (CfA).

CAMBRIDGE, MASSACHUSETTS (BNS): Researchers have detected pulses of gamma rays with energies exceeding 100 billion electron-volts (100 GeV) -- a million times more energetic than medical X-rays and 100 billion times more than visible light.

An international team of scientists who reported the discovery said, the gamma rays come from an extreme object at the Crab Nebula's center known as a pulsar.

A pulsar is a spinning neutron star -- the collapsed core of a massive star. Although only a few miles across, a neutron star is so dense that it weighs more than the Sun.

Rotating about 30 times a second, the Crab pulsar generates beams of radiation from its spinning magnetic field, the CfA said in a release.

The beams sweep around like a lighthouse beacon because they're not aligned with the star's rotation axis. So although the beams are steady, they're detected on Earth as rapid pulses of radiation.

The gamma-ray pulses were detected by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) -- the most powerful very-high-energy gamma-ray observatory in the Northern Hemisphere.

Astronomers observe very-high-energy gamma rays with ground-based Cherenkov telescopes. These gamma rays, coming from cosmic "particle accelerators," are absorbed in Earth's atmosphere, where they create a short-lived shower of subatomic particles.

The Cherenkov telescopes detect the faint, extremely short flashes of blue light that these particles emit (named Cherenkov light) using extremely sensitive cameras.

The images can be used to infer the arrival direction and initial energy of the gamma rays.