Glossary term: X-ray
Description: X-rays are electromagnetic waves that are less energetic than gamma radiation, but have higher energies than ultraviolet radiation. The X-ray part of the spectrum is commonly defined as the wavelength range between 10 picometers and 10 nanometers. This corresponds to frequencies between about 30 petahertz and 30 exahertz. The energies of the resulting photons (light particles) are in the range between about 100 eV and 100 keV, using the unit "electron volt" that is common in particle physics.
In astronomy, significant X-ray emission typically reaches us from regions containing gas or plasma at very high temperatures, higher than a million kelvins. Examples include the corona of our Sun and the coronae of other stars, and also the accretion disks around compact objects: gas falling towards a neutron star or black hole, and swirling around in an extremely hot disk before falling onto or into the central object. Supernova remnants are another common class of astronomical X-ray source: when a massive star explodes as a supernova at the end of its life, the star's outer layers are flung into space. Where that flung-out gas encounters the surrounding interstellar medium, shock effects will heat up matter in the collision region to high temperatures, resulting in the production of X-rays.
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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher
The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".
