The Chandra X-ray Observatory is a space telescope designed to detect x-ray sources in outer space. It is part of NASA's Great Observatories program, which includes the Hubble Space Telescope, Spitzer Space Telescope, and the Compton Gamma Ray Observatory. The Chandra X-ray Observatory is named after the Indian-American physicist Subrahmanyan Chandrasekhar, who worked out the mass limit for white dwarfs to become neutron stars.
The concept of a space telescope was first articulated in the 1940s, shortly after the end of WWII. It was not until the launch of the Hubble Space Telescope in 1990 that this was finally realized. Chandra was launched in 1999, the third of the Great Observatories to be put into operation. Because the atmosphere absorbs the majority of x-rays, Chandra is in a unique position to do x-ray astronomy.
X-rays are produced in abundance by energetic astronomical objects and phenomena, such as black holes, neutron stars, and supernovae. Chandra has looked into the centers of numerous supernova relics (planetary nebulae) and discovered the compact objects that remain, which are black holes or neutron stars. It has observed x-ray emissions from Sagittarius A*, a supermassive black hole at the center of the Milky Way galaxy.
Chandra may have even observed stars even more compact and dense than neutron stars (which are only as large as a city but contain the mass of an entire star) — quark stars — although this is still in debate. By observing collisions between galactic superclusters, Chandra has helped verify the existence of so-called "dark matter" — invisible matter that is only observed indirectly, through its gravitational influence on visible matter. It has observed x-ray emissions from material in protoplanetary discs orbiting far-away stars, observations that give us insight into how our solar system formed.
The Chandra satellite, in a highly eccentric orbit averaging 10,000 km above the surface, has a mass of 4,800 kg (10,600 lb), and makes a complete circle around the Earth every 64.3 hours. The diameter of the craft is 1.2 meters (3.9 ft).