sess12 - 12. Blast waves and supernova remnants Reading:...

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12. Blast waves and supernova remnants Reading: Shu, Vol.II, Ch.17 12.1 Self-similarity and scales In galaxies one fnds a many sources oF shock waves and the interstellar medium is signifcantly in±uenced by the shocks. These shocks can arise From strong stellar winds and From stellar explosions, supernova. Supernovae are caused by run-away thermonuclear reactions that occur when stellar cores collapse. A type I supernova involves a white dwarF that exceeds the Chandrasekhar mass limit on account oF accretion From another star in close orbit. A type II supernova happens For massive stars when the iron core, For which no more energy gain by Fusion is possible, exceeds the Chandrasekhar limit. A typical kinetic explosion energy is 10 51 ergs or 10 - 3 M ¯ c 2 . In both cases the outer layers oF the star are expelled or ejected with high velocity, which creates a strong shock when the ejecta meet the circumstellar medium. The latter may be dilute gas For a type I supernova or hot, dense, and magnetized stellar wind material For a type II supernova. Much oF the astrophysics modeling oF supernova explosions and their remnants derives From the nuclear bomb research programs in the East and West. The problem is essentially one oF a point release oF an enormous amount oF energy, E , into a static homogeneous medium oF mass density ρ u . In the initial phase oF the expansion the impact oF the external medium will be small, For the mass oF the ambient medium, that is overrun and taken along, is still small compared with the ejecta mass. The supernova remnant is said to expand adiabatically. AFter some time the mass swept up by the outwardly moving shock wave will signifcantly exceed the mass oF the initial ejecta. The ram pressure, ρ u U 2 sh oF the matter that enters the shock wave may still be much larger than the thermal pressure oF the upstream medium, P u . Let us assume that the radiative energy loss is much smaller than the initial available energy
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This note was uploaded on 02/29/2012 for the course PHYS 227 taught by Professor Rabe during the Fall '08 term at Rutgers.

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sess12 - 12. Blast waves and supernova remnants Reading:...

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