The European Space Agency (ESA) plans to launch the satellite in April 2001 and use it to study hard X-ray and gamma-ray sources in the energy range 15 keV to 10 MeV. A full-scale structural and thermal model of the telescope has just been completed ready for testing.
There will be two main instruments on board. A spectrometer made of high-purity germanium will measure gamma-ray energies extremely precisely whilst an imager will record their position in the sky.
With a resolution of 12 arc-minutes it is the imager that excites astronomers the most. Current telescopes, such as NASA's Compton Gamma Ray Observatory, have difficulty pinpointing the source of gamma-ray emissions sufficiently to match them up with objects seen at other wavelengths.
A breakthrough came last year when the Italian Bepposax X-ray satellite identified the origin of a gamma ray burst. The observations showed the burst came from a galaxy towards the edge of the visible universe and must therefore be incredibly energetic way over 1050 ergs, more than the energy released by all the 1011 stars in our Galaxy over several days! The mechanism fuelling gamma-ray bursts remains a mystery that astronomers hope Integral will help to solve.
Astronomers will also use Integral to study active galaxies and, nearer to home, to see close up to the accretion discs surrounding black holes.
Meanwhile, Integral's spectrometer will be used to measure the emission lines of heavy elements ejected into space by the supernova explosion at the end of a heavy star's lifetime.