X-ray astronomy

The X-ray astronomy is a part of the field of astronomy, which uses light emitted by celestial objects x-rays. How many regions of the electromagnetic spectrum is used x-rays until the second half of the 20th century for astronomical observations.

Observation area

In astronomy, is among the most X-ray range of electromagnetic radiation between energies of about 0.1 to 500 keV, ie wavelengths between about 12 nm and 2.5 pm understood. Often radiation below about 2 keV is referred to as ' soft ', also as ' hard ' X-rays. Adjacent areas are the ultraviolet astronomy and gamma-ray astronomy.


Since the Earth's atmosphere is opaque to X-rays, X-ray astronomy became possible only after the Second World War with rockets and satellites. In the hard X-ray and high-flying balloons were partially used. Meanwhile, a large number of space telescopes has been started for the X-ray range, see the list of X-ray satellites.


Normal telescopes used for visible light are useless for X-rays, because their levels do not reflect the X-rays. In the range up to about 10 keV Wolter telescopes in use today. They are based on the total reflection of X-rays at very shallow, grazing incidence on a metal surface. A Wolter telescope used for astronomy is nowadays usually consist of several nested mirror shells. The effective collecting surface for X-ray photons is a function of the energy and significantly smaller than the entire entrance surface of the mirror assembly. At high energies Wolter telescopes are no longer usable. Mechanical collimators are used instead, absorb X-rays from outside the target direction, or complex " coded masks " from their shadows on the detector, the direction of the source can be reconstructed.


For the wide energy range of X-ray astronomy a plurality of detector principles were used, how they are used in a similar form in nuclear physics and particle physics. Today, the most common are CCD sensors. In shape are used as X-ray detector to produce not only a two dimensional image, but also measure the energy of the incoming X-ray photons, thus allowing a simple form of spectroscopy.

Objects of observation of X-ray astronomy

For a long time the X-ray astronomy has mainly focused on specific high-energy objects such as X-ray binaries and active galactic nuclei. Meanwhile, however, it contributes to many areas of astrophysics, and we know many different types of astronomical X-ray sources.


As the first cosmic X-ray source was identified in September 1949 on a flight with a converted V-2 rocket, the corona of the sun. A surprising breakthrough Riccardo Giacconi and employees on 18 June 1962 with an experiment on an Aerobee rocket, which was to search for reflected from the lunar surface X-ray radiation from the sun. Instead of the moon they found the first bright X-ray binary star in our Milky Way, Scorpius X- 1, as well as the cosmic X-ray background. This result marked the beginning of a stormy development, first with another rocket and balloon experiments and later with X-ray satellites. 1971 were detected in the first survey of the entire sky with the Uhuru satellite 339 sources. HEAO -2 ( "Einstein Observatory " ) was the first large X-ray telescope with good spatial resolution. With over 100,000 ROSAT X-ray sources were found in the entire sky in the 1990s. The most important currently active X-ray telescopes are Chandra and XMM -Newton.