A supernova is the cataclysmic explosion of a star which, for a time, may shine brighter than a galaxy whole made up of hundreds of billions of stars. There are essentially two main families of supernovae: the SN II and SN Ia.
Extract from the documentary From the Big Bang to the living. Jean-Pierre Luminet talks about the death of massive stars, their explosions in supernovae and the formation of pulsars. © ECP Productions, YouTube.
Two families of supernovae
SN II occurs when massive stars larger than about 8 to 10 masses solar cells have exhausted their combustible nuclear. This causes thecollapse gravitational heart whose force of gravity is no longer counterbalanced by the pressure of radiation released by thermonuclear reactions. According to a still poorly understood scenario, a large amount ofenergy is released and ejects the outer layers of the star to leave only one neutron star or, in extreme cases, a black hole.
SN Ia occur in a binary system which contains at least one white dwarf. It is probably fair to say that many textbooksastrophysics at least ten years old explain the origin of SN Ia supernovae with a white dwarf accreting matter until reaching the famous mass Chandrasekhar limit. We know that the stars of the Milky Way mainly evolve in pairs. Many are less massive than the Sun, and like him, they will end their life peacefully as a white dwarf. In theory at least, because if they are part of a binary system containing a star that has not yet reached the same stage of evolution, their fate can be much more spectacular. So if they are close enough to a red giant, or even a star still in the main sequence, the tidal forces of the white dwarf can be such that a transfer of matter from the star to the dwarf takes place. product, increasing its mass.
When this reaches 1.4 solar mass, the laws of Quantum mechanics and some Relativity inevitably make it unstable and it must collapse. The process triggers above all thermonuclear reactions of fusion from carbon andoxygen and then an explosion occurs, blowing the whole star.
As this explosion takes place at constant mass, its brightness intrinsic should vary slightly. This being very important, the SN Ia are therefore good indicators of distance to probe theuniverse observable and study its expansion to billions oflight years of the Milky Way. It is precisely these properties that have enabled Saul perlmutter and his colleagues to highlight the accelerated expansion of the observable cosmos.
It is now believed that many SN Ia would be collisions of white dwarfs.
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