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Originally Posted by nekokami
HarryT, do you have a particular edition of Plato's "Phaedo" to recommend?
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You could try my "complete works of Plato" right here on MR
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And I hadn't realized that only binary stars can nova-- I knew our sun wasn't big enough for a supernova, and that yellow G stars don't go nova (according to Larry Niven, anyway), but only binaries? Really? Wow. This has been an interesting day.
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The way that a nova happens is that you have a white dwarf star and a "giant" star in close orbit around one another. The outer atmosphere of the giant star "accretes" on the surface of the white dwarf. After a few million years, the density of the accreted matter reaches a critical density and it "blows off" in a huge nuclear explosion. The entire process then starts all over again.
If the dwarf star is rather more massive, then the build-up of matter on its surface can push the density of the entire star over a critical limit, and the star blows itself to bits in a hugely more energetic
supernova explosion - technically, what's called a "Type 1a supernova". These are very important to astronomers, since they happen when the star reaches a very specific, fixed mass, and hence the resulting explosion is of a fixed "brightness". They are so enormously bright that they can be seen in extremely distant galaxies, and the fact that we know how bright they "really" are, and we can measure how bright they seem to be, this gives us a very accurate way of measuring how far away that galaxy is from us.