Added 1 new A* page:Dead stars 'can re-ignite' and explode (BBC) talks about how thanks to the study of a Type Ia supernova whose gamma rays were detected reaching Earth from nearby galaxy M82 starting on January 21st of this year, scientists finally obtained proof, by spectrographic analysis of the elements in the explosion, that a white dwarf star, usually kind of the end of a star's evolution, can, if it somehow collects enough mass to pass the Chandrasekhar limit of ~1.39 solar masses, begin nuclear fusion of the carbon at its core, starting a reaction that suddenly tears the star apart. These Type Ia supernovae, because they occur specifically at that ~1.39 solar masses star size, are quite handy for determining distances to neighboring galaxies or star clusters, because, since the mass of the exploding star is always the same, and brightness diminishes with a simple formula based on distance, measuring the brightness of the explosion tells you precisely how far away the supernova and its neighboring stars must be.
Type Ia supernovae are also the sources of the iron we have here on Earth: in the reaction, the white dwarf's carbon and oxygen fuse into radioactive nickel, which decays into radioactive cobalt, which decays into iron. And that's why our blood is red! Sorta.
One interesting note from the observations of that Jan. 21st supernova was that by 50 to 100 days after the explosion, "the white dwarf has already expanded to a size larger than our solar system."
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