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.
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 .
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 .
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- Keith Arnaud, et al .: Handbook of X-ray Astronomy. Cambridge University Press, Cambridge 2011, ISBN 978-0-521-88373-3 .
- Where does X-ray radiation come from in space? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Dec 5, 1999.
- The Multiwavelength Astronomy Gallery 
- Introduction to X-ray Astronomy at the Max Planck Institute for Extraterrestrial Physics
- Welcome to the World of X-ray Astronomy NASA Goddard Space Flight Center
- Keith Arnaud, et al .: Handbook of X-ray Astronomy. Cambridge University Press, Cambridge 2011, ISBN 978-0-521-88373-3 , p. 1.