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Shock waves are common in astrophysical environments[1]. Several examples of astrophysical shock waves are: Supernova remnants driving a shock through the interstellar medium (ISM). The Earth's bow shock. Shocks traveling through a massive star as it explodes in a core collapse supernova.[2] Shocks in interstellar gas, cased by a collision between molecular clouds or by a gravitational collapse of a cloud. Accretion shocks at the edge of galaxy clusters. Because of its low density, most shocks in the interstellar medium are collisionless. This means that the shocks are not formed by two body Coulomb collisions, since the mean free path for these collisions is too large. It is widely accepted that the mechanism driving these shocks consists of plasma instabilities, that operate on the scale of plasma skin depth, which is typically much shorter than the mean free path. It is known that shocks in astrophysical systems have extremely high energy particles in them, though the evidence has not yet well established a definite answer about whether the particles emitting high energy photons are protons, electrons or both. The common picture of how these particles accelerate is called Fermi acceleration. It is usually agreed that shocks caused by supernova remnants expanding in the interstellar medium accelerate the cosmic rays measured above the Earth's atmosphere.[3] Shock waves in stellar environments, such as shocks inside a core collapse supernova explosion often become radiation mediated shocks. Such shocks are formed by photons colliding with the electrons of the matter, and the downstream of these shocks is dominated by radiation energy density rather than thermal energy of matter. An important type of astrophysical shock is the relativistic shock. These shocks are unique to astrophysical environments, and can be either collisionless or radiation mediated. Relativistic shocks are theoretically expected in gamma ray bursts, active galactic nucleus jets and in some types of supernova explosions. References ^ ZELDOVICH, Y.B., PHYSICS SHOCK WAVES 1,2 ^ The structure of supernova shock waves, T.A. Weaver, 1976ApJS...32..233W ^ M. S. Longair, High Energy Astrophysics Vol 1,2, Cambridge University Press This physics-related article is a stub. You can help Wikipedia by expanding it. v • d • e