History of X-Ray Astronomy
X-Ray Instruments Detect Neutron Stars and Black Holes
The first hint that cosmic X-rays exist came in 1949, when radiation detectors
aboard rockets were briefly carried above the atmosphere where they detected
X-rays coming from the Sun. It took more than a decade before a greatly improved
detector discovered X-rays coming from sources beyond the solar system.
Some of the major X-ray astronomy missions include:
In the early 1970's, NASA's Uhuru X-ray satellite, equipped with a
relatively simple instrument - a sensitive X-ray detector similar to a Geiger
counter attached to a viewing pipe to locate the source -- made some astounding
discoveries. Uhuru detected evidence of black holes and superdense neutron stars
pulling matter from companion stars, and vast expanses of hot gas in gigantic
systems containing thousands of galaxies.
The first large focussing X-ray telescope
was the Apollo Telescope Mount aboard Skylab in the early 1970's. This pioneering
telescope used two pairs of concentric mirrors to make stunning X-ray images of
the Sun. It set the stage for the development of the Einstein X-ray
NASA's Einstein Observatory, launched in 1978, was the first large X-ray
telescope with mirrors. It made the first X-ray images of shock waves from
exploded stars, and images of hot gas in galaxies and clusters of galaxies.
Einstein also located accurately over 7000 X-ray sources and made possible a new
way to study the mysterious dark matter that surrounds many galaxies.
The Roentgensatellite or ROSAT, a
joint venture between Germany, the United Kingdom and the United States, carried
an even larger X-ray telescope into orbit in 1990. It has expanded the number of
known X-ray sources to more than 60,000 and has proved to be especially valuable
for investigating the multi-million degree gas present in the upper atmospheres
of many stars.