COMPTON followed the Hubble into space via a space shuttle ride in 1991.
The Compton Gamma Ray Observatory followed the Hubble into orbit in 1991. Weighing in at 17 tons, it was then the heaviest payload lofted by a space shuttle. Compton's mission was to see the cosmos in the mysterious light of very high-energy photons, which make up gamma rays. So far, Compton has probed the nature of solar flares, gamma ray bursts, black holes and quasars.

Named for Arthur Holly Compton, who won the 1927 Nobel Prize in physics for research that is the underpinning of gamma-ray detectors, this observatory carries four different instruments that span the far end of the electromagnetic spectrum. Astronomers working with each device have made important, and often surprising, discoveries.

MILKY WAY. Our home galaxy glows with gamma radiation in this image made by Compton's Energetic Gamma Ray Experiment Telescope (EGRET).

BATSE, the Burst and Transient Source Experiment, is to study the brief but extremely powerful bursts of gamma rays that flash throughout the universe. Measurements made by BATSE have demonstrated that these gamma bursters are not localized but seem to come from all parts of the cosmos. Moreover, no two have ever been the same. Researchers speculate that seemingly more powerful bursts are simply from closer regions.

A detector known as EGRET (Energetic Gamma Ray Experiment Telescope) has produced an all-sky map showing emissions of gamma radiation through the Milky Way. Three of the six gamma ray pulsars identified so far were discovered with Compton. EGRET also found a new class of cosmic denizens, which astronomers call gamma-ray blazers. They appear to be very distant; unlike the rapidly varying pulsars, their peaks of energy occur on a time scale of days.

Another map, made by COMPTEL (Imaging Compton Telescope), scans the Milky Way in the very narrow band of gamma radiation emitted by radioactive aluminum 26; it shows curiously high concentrations of this isotope in small areas of the galaxy. COMPTEL images have also revealed two pulsars, a blazer and a possible black hole.

Meanwhile, OSSE (Oriented Scintillation Spectrometer Experiment) can detect the gamma rays produced when positrons and electrons collide and annihilate each other in the interstellar medium. It has found direct evidence of high energy particles smashing into the Sun and exciting nuclei, which then emit gamma radiation.

Images: NASA