Nasa has launched a space observatory with a mission to investigate sources of high-energy gamma rays.

The Gamma ray Large Area Space Telescope, or Glast, can see about 20 per cent of the sky at any given time and will scan the whole sky every three hours.

Glast can detect bursts of gamma rays and swing the telescope to receive them.

Gamma rays are short-wavelength high-energy electromagnetic radiation. Sources include pulsars, quasars and the black holes and exploding stars at the centre of galaxies.

It has also been postulated that gamma rays are emitted by short-lived dark matter particles annihilating one another.

Gamma rays cannot penetrate Earth's atmosphere, so Glast will orbit at 350 miles above the surface.

The last gamma ray survey of space revealed over 270 new sources, two thirds of which have never been identified.