Gamma-ray Astronomy

• see also:
  • astronomy index and links
  • infra-red astronomy

Introduction:

• the field of gamma-ray astronomy slowly emerged during the 1960's
• because earth's atmosphere blocked gamma-rays from reaching the ground, it took the 1st rudimentary expts on balloons and satellites to unveil the high-energy universe.
• gamma-ray detection:
  • highest energy gamma-rays (trillion electron volts) penetrating deep into earth's atmosphere, collide with air molecules & create showers of secondary particles and radiation producing Cherenkov light. Ground based detectors called Cherenkov telescopes actually detect these secondary effects.
  • high energy rays of 30million to 30 billion eV interact with detectors, each producing an electron and positron that reveal the direction & energy of the photon.
  • medium energy rays of 1-30million eV interact with detectors via Compton scattering in which the gamma-ray collides with an electron in the detector and imparts energy to it
  • lower energy rays 30,000 to 1million eV are measured via photoelectric effect.
• Explorer 11 was the original gamma-ray satellite
• the Compton Gamma-Ray Observatory (CGRO) - a sister to the Hubble Space Telescope that orbited 1991-2000- raised the count of gamma-ray sources from 40 to 400 and detected more than 2,700 gamma-ray bursts, establishing the latter as the most powerful explosions in the universe. Soon other scientists came to understand what gamma-ray astronomers had known all along: gamma rays offer unique insights to lingering mysteries such as the history of star formation, the fate of matter around black holes, the creation of relativistic jets, and the nature of fundamental physical forces.
• in the early 21stC, gamma-ray astronomy is entering its golden age with launch of:
  • European Space Agency's International Gamma-Ray Astrophysics Laboratory (Integral) in Oct 2002
  • several more in the next few years

Gamma-Ray Bursts:

• Gamma ray bursts (or GRBs) are the most powerful known explosions in the Universe.
• Although astronomers aren't exactly sure what causes them, they're somehow linked to supernovae explosions - it could be the formation of a black hole after the supernova explodes.
• When a GRB goes off, it funnels a tremendous amount of energy into two lighthouse-like beams that would probably vaporize anything out to 200 light-years away.
• Fortunately there aren't any stars in our galactic neighborhood that has the potential to explode as a supernova, so we're probably safe from such an event, but astronomers will keep looking… just to be sure.