1999

Chandra X-ray Observatory

In 1895 the German physicist Wilhelm Röntgen discovered a mysterious form of radiation created in high-voltage cathode-ray-tube experiments. He dubbed the unknown type of radiation X-rays. Twentieth-century physicists eventually learned that X-rays can be created by electrons accelerated to high velocities in laboratory experiments or in high-energy astrophysical events, such as supernova explosions. The astronomical study of X-ray sources was severely limited, however, by the fact that the Earth’s atmosphere absorbs most X-rays generated by cosmic events. A space-based platform was needed.

In 1978 NASA launched the Einstein X-ray imaging satellite to conduct the first space-based observations of high-energy cosmic X-ray sources. For nearly three years Einstein surveyed the sky, studying the details of supernova explosions and identifying new X-ray sources. The success of Einstein compelled astronomers to propose a more sensitive, higher-resolution X-ray space telescope mission as part of NASA’s Great Observatories program—four space telescopes designed to allow astronomers to make measurements that are impossible to make from Earth-based telescopes.

After more than 20 years of development effort, NASA’s Advanced X-ray Astrophysics Facility space telescope, renamed Chandra after the Indian-American astrophysicist Subrahmanyan Chandrasekhar, was launched in 1999. Expected to last only five years, Chandra has now operated for more than a dozen years, taking data on supernovae, pulsars, gamma-ray bursts, supermassive black holes, brown dwarfs, and dark matter.

Artist’s rendering of the Chandra X-ray Observatory.

Like its Great Observatory cousins the Hubble Space Telescope, Compton Gamma Ray Observatory, and the Spitzer Space Telescope, Chandra has completely revolutionized an entire subfield of astronomy and astrophysics, opening an orbital telescopic window into violent, high-energy environments in the cosmos that would otherwise have been impossible to study.

SEE ALSO “Daytime Star” Observed (1054), Brahe’s “Nova Stella” (1572), White Dwarfs (1862), Dark Matter (1933), Black Holes (1965), Pulsars (1967), Hubble Space Telescope (1990), Spitzer Space Telescope (2003).

A composite Hubble Space Telescope (pink) and Chandra X-ray Observatory (green and blue) image of supernova remnant 0509-67.5, from a stellar explosion 160,000 light-years away in the Large Magellanic Cloud.