X-ray astronomy

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The X-ray astronomy is a part of astronomy , that of celestial objects emitted X-rays uses. Like many areas of the electromagnetic spectrum , X-rays have only been used for astronomical observations since the second half of the 20th century.

Observation area

In astronomy, X-ray radiation usually refers to the range of electromagnetic radiation between energies of about 0.1 to 500  keV , i.e. H. Understand wavelengths between about 12  nm and 2.5  pm . Radiation below about 2 keV is often referred to as 'soft' and above that as 'hard' X-ray radiation. Adjacent areas are ultraviolet astronomy and gamma astronomy .


Since the earth's atmosphere is impermeable to X-rays, X-ray astronomy only became possible with research rockets and satellites after the Second World War. In the hard X-ray area, soaring balloons were sometimes used. In the meantime a large number of space telescopes for the X-ray sector have been launched, see also the list of X- ray satellites .


Quadruple nested wolf telescope of the Chandra space telescope (Illustration: NASA)

Normal telescopes used for visible light are unusable for X-rays because their mirrors do not reflect the X-ray light. Wolt telescopes are used today in the range up to about 10 keV . They are based on the total reflection of X-ray light at very flat, grazing incidence on a metal surface. A Wolter telescope used for astronomy today usually consists of several nested mirror shells. The effective collecting area for X-ray photons depends on the energy and is significantly smaller than the entire entrance area of ​​the mirror arrangement. Wolt telescopes can no longer be used at high energies. Instead, mechanical collimators are used that absorb X-rays from outside the target direction, or complex “coded masks”, from whose shadows cast on the detector, the direction of the sources can be reconstructed.


A large number of detector principles were used for the wide energy range of X-ray astronomy, as they are used in a similar form in nuclear physics and particle physics . The most common today are CCD sensors . In their form, used as an X-ray detector, they not only generate a two-dimensional image, but also measure the energy of the incoming X-ray photons, thus allowing a simple form of spectroscopy .

Observation objects in X-ray astronomy

For a long time, X-ray astronomy has mainly focused on certain high-energy objects such as X-ray binary stars and active galactic nuclei . However, it now contributes to wide areas of astrophysics, and many different types of astronomical X-ray sources are known .


The corona of the sun was identified as the first cosmic X-ray source in September 1949 during a flight with a converted V2 rocket. Riccardo Giacconi and co-workers achieved a surprising breakthrough on June 18, 1962 in an experiment on an Aerobee rocket that was supposed to search for X-rays from the sun reflected from the lunar surface. Instead of the moon, they found the first bright X-ray binary star in our Milky Way, Scorpius-X-1 , and the cosmic X-ray background. This result was at the beginning of a stormy development, first with further rocket and balloon experiments and later with X-ray satellites . In 1971, the first Uhuru satellite survey of the entire sky discovered 339 sources. HEAO-2 (“Einstein Observatory”) was the first large X-ray telescope with good spatial resolution. With ROSAT , over 100,000 X-ray sources were found all over the sky in the 1990s. The most important currently active X-ray telescopes are Chandra and XMM-Newton .


  • Lars L. Christensen, (et al.): Hidden Universe. WILEY-VCH, Weinheim 2009, ISBN 978-3-527-40868-9 .
  • Simone Jüngling: X-ray astronomy in Germany - history of origin, institutionalization and instrumental developments. Kovač, Hamburg 2007, ISBN 978-3-8300-2977-9 .
  • JA Bleeker: X-ray and gamma-ray astronomy. Pergamon Pr., Oxford 1989, ISBN 0-08-040158-9 .
  • Nicholas E. White: X-ray astronomy. American Inst. Of Physics, Melville 2001, ISBN 0-7354-0043-1 .
  • Keith Arnaud, et al .: Handbook of X-ray Astronomy. Cambridge University Press, Cambridge 2011, ISBN 978-0-521-88373-3 .


Web links

Individual evidence

  1. Keith Arnaud, et al .: Handbook of X-ray Astronomy. Cambridge University Press, Cambridge 2011, ISBN 978-0-521-88373-3 , p. 1.