X-ray Astronomy

X-ray radiation lies on the opposite side of the electromagnetic spectrum from Infrared radiation.  Thus, X-rays have much shorter wavelengths and much higher energies than visible light.  A typical X-ray photon has an energy 1000 times that of a visible photon.  Astronomers classify X-rays by their energy.  ‘Soft’ X-rays have energies between 0.1 and 1.0 keV, while ‘Hard’ X-rays have energies between 1.0 and 10.0 keV.  By definition, 1 eV (electronvolt) is the amount of energy gained (or lost) by the charge of an electron moved across an electric potential difference of one volt.  

X-ray astronomy is a fairly new field of study, because it can only be done from satellites.  Water absorbs radiation at these wavelengths, so our atmosphere is opaque to X-rays.  The diagram below gives a quick overview of what wavelengths of electromagnetic radiation are absorbed by our atmosphere.


Many exotic astrophysical objects emit X-ray radiation including black holes, active galactic nuclei (AGN), pulsars, galaxy clusters, and binary systems containing a white dwarf, neutron star, or black hole.  In supernova remnants, strong X-ray emission traces the strong shock wave and hot shocked gas.  After a supernova, material from the explosion races outwards and plows into the surrounding gas.  The hot gas and high-energy particles created at this shock front glow at a range of wavelengths (radio through X-ray) for thousands of years.  An image of Kepler’s supernova remnant at several wavelengths is shown below.  The green coloring indicates low energy X-rays while the blue indicates high energy X-rays.


At the moment, there are two major X-ray satellites that are currently operating and taking data.  XMM-Newton was launched by the European Space Agency (ESA) in 1999.  It has better spectral resolution and a larger field of view than Chandra.  The Chandra X-Ray Observatory was also launched in 1999 by NASA and is currently operated by the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA.  Chandra has much better spatial resolution than XMM-Newton.

If you are interested in learning more about X-ray astronomy, check out this overview from the University of Cambridge:

Introduction to X-ray Astronomy

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