One particularly dynamic category of astronomical objects is the supernovae.
Supernovae occur primarly within two main categories of progenitors.
- Core Collapse in a Massive Star (Type IIb/c)- This is perhaps the most widely explained cause for a supernova, and, in fact, about 3/4 of all supernovae fall into this category. The progenitor for such an event is a very massive (> 10 x solar mass) star, which has evolved off the hydrogen fusion driven "main sequence." I'll take some time now to explain the classic "onion skin" model for the cores of very massive evolved stars. As explained last time ("All Stars Equal?"), as the star begins to run out of hydrogen fuel for nuclear burning, helium settles to the center of the core, increasing the heat and density in the center. Hydrogen begins to burn in a shell around the extremely hot helium core, like water on a hot stove. Eventually the core is hot enough for helium to fuse in the "helium flash," and the entire core detonates, then settles down and begins to fuse helium regularly in a sort of second main sequence, called the "horizontal branch," or "red clump." In stars like the sun, this is about it, and after 100 million years or so, the helium burning starts to die down, and all that's left is the remanant carbon/oxygen core, now called a "white dwarf." In very massive stars, however, the carbon and oxygen core becomes hot enough to fuse yet again, so there's a "carbon flash," and this process repeats with flashes of various elements descending down the periodic table, until finally the core is burning iron. The iron (56) nucleus, unfortunately for the star, has the least energy per nucleon of any nucleus, and so fusing iron atoms actually spends energy rather than producing it. Suddenly, the core is dumping a large amount of energy into producing higher elements, with no heat output. With no heat, there is no gas pressure to resist gravity. The only thing holding up the core is the electron shells of the atoms which are stacked like bricks, each touching the another, staving off collapse as long as possible. Gravity, however, will win this battle through a process called inverse beta decay, where gravity forces the nuclei to eat their own electrons (and burp out neutrinos, one per electron). Now the number of electrons consumed is basically the mass of the core divided by the mass of a proton, approximately the number of electrons in the sun, which is about 1057. These neutrinos have a very large amount of energy each, so when 1057 are released within seconds, an
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