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The part keeping a star together is its gravitational pull to all of its pieces. The part keeping it from collapsing is the outward push of its fusion (and also

The part keeping a star together is its gravitational pull to all of its pieces. The part keeping it from collapsing is the outward push of its fusion (and also the electrons pushing against each other since they can't all occupy the same space). This is usually balanced and you have a nice star. When the fusion slows as the star exhausts fuel, gravitational pull dominates and everything falls inward in a collapse. That presses the inner bits together nice and tight, and then the outer bits bounce off it. So you have a collapse inward with an explosion as everything bounces off. Wikipedia has a nice picture.

dredmorbius 3y ago
The first time I came to understand this was in Isaac Asimov's The Collapsing Universe, which described how stars form, function, and die, with the ultimate fate of the very largest being black holes. <https://archive.org/details/collapsinguniver0000asim https://archive.org/details/collapsinguniver0000asim> Stars are a contest between gravity and the nuclear strong force, with stellar fusion creating the heat and pressure required to resist, at least for a time, the pull of gravity. The larger a star, the faster it burns through its hydrogen fuel. While brown dwarf stars may have liftimes in the trillions of years, our Sun will expend all its fuel in about 11-12 billion years (it's about half-way through that process now), and will gradually grow hotter and brighter as it does so (it's already about 25% brighter than it was when the Earth was formed). The largest stars have lifespans of only a few million years, roughly dating to when the proto-hominids diverged from their last common ancestor with chimpanzees, and far more recently than the dinosaurs died out. It's a useful lesson to recall that bigger and more energy-hungry does not necessarily mean longer-lived, and quite often means precisely the opposite. <http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/startime.html http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/startime.ht...> <https://en.wikipedia.org/wiki/Stellar_evolution https://en.wikipedia.org/wiki/Stellar_evolution>

dredmorbius 3y ago

The first time I came to understand this was in Isaac Asimov's The Collapsing Universe, which described how stars form, function, and die, with the ultimate fate of the very largest being black holes. <https://archive.org/details/collapsinguniver0000asim https://archive.org/details/collapsinguniver0000asim> Stars are a contest between gravity and the nuclear strong force, with stellar fusion creating the heat and pressure required to resist, at least for a time, the pull of gravity. The larger a star, the faster it burns through its hydrogen fuel. While brown dwarf stars may have liftimes in the trillions of years, our Sun will expend all its fuel in about 11-12 billion years (it's about half-way through that process now), and will gradually grow hotter and brighter as it does so (it's already about 25% brighter than it was when the Earth was formed). The largest stars have lifespans of only a few million years, roughly dating to when the proto-hominids diverged from their last common ancestor with chimpanzees, and far more recently than the dinosaurs died out. It's a useful lesson to recall that bigger and more energy-hungry does not necessarily mean longer-lived, and quite often means precisely the opposite. <http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/startime.html http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/startime.ht...> <https://en.wikipedia.org/wiki/Stellar_evolution https://en.wikipedia.org/wiki/Stellar_evolution>