Because of the low ambient density, most astronomical shocks 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, often exceeding the size of the system. Such shocks were first theorised by Frederic de Hoffmann and Edward Teller,[2] who studied shock waves in magnetized fluids with infinite conductivity. The precise mechanism for energy dissipation and entropy generation at such shocks is still under investigation, but it is widely accepted that the general mechanism driving these shocks consists of wave particle interaction and 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 collisionless shocks are associated with extremely high energy particles, although it has not been definitively established if the high energy photons observed are emitted by protons, electrons or both. The energetic particles are in general believed to be accelerated by the Fermi acceleration mechanism. 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, in which the shock velocity is a non-negligible fraction of the speed of light. 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 supernovae.
shock, waves, astrophysics, shock, waves, common, astrophysical, environments, examples, shock, waves, found, astrophysics, herbig, haro, object, left, supernova, remnants, right, because, ambient, density, most, astronomical, shocks, collisionless, this, mean. Shock waves are common in astrophysical environments 1 Examples of shock waves found in astrophysics Herbig Haro object left and supernova remnants right Because of the low ambient density most astronomical shocks 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 often exceeding the size of the system Such shocks were first theorised by Frederic de Hoffmann and Edward Teller 2 who studied shock waves in magnetized fluids with infinite conductivity The precise mechanism for energy dissipation and entropy generation at such shocks is still under investigation but it is widely accepted that the general mechanism driving these shocks consists of wave particle interaction and 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 collisionless shocks are associated with extremely high energy particles although it has not been definitively established if the high energy photons observed are emitted by protons electrons or both The energetic particles are in general believed to be accelerated by the Fermi acceleration mechanism 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 in which the shock velocity is a non negligible fraction of the speed of light 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 supernovae Examples editInterplanetary shock waves due to solar flares and coronal mass ejections and originally discovered via geomagnetic sudden commencements The bow shocks formed around planets in stellar winds and sometimes around stars themselves Supernova remnants driving a shock through the interstellar medium ISM Shocks traveling through a massive star as it explodes in a core collapse supernova 4 Shocks in interstellar gas caused by a collision between molecular clouds or by a gravitational collapse of a cloud Accretion shocks at the edge of galaxy clusters References edit ZELDOVICH Y B PHYSICS SHOCK WAVES 1 2 De Hoffmann F Teller E 1950 11 15 Magneto Hydrodynamic Shocks Physical Review 80 4 692 703 Bibcode 1950PhRv 80 692D doi 10 1103 PhysRev 80 692 M S Longair High Energy Astrophysics Vol 1 2 Cambridge University Press The structure of supernova shock waves T A Weaver 1976ApJS 32 233W nbsp This astrophysics related article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Shock waves in astrophysics amp oldid 1189239540, wikipedia, wiki, book, books, library,
