Inspired in part by this thread, I’m wondering how far must a star wander down the periodic path before it blows? I mean, must it get all the way to Manganese before Iron says, “No more fusion for you!” or can a huge red giant like Antares or Betelgeuse give it up once all the H is fused to He?
IANA a rocket surgeon but Wikipedia seems to suggest that it depends on the type of supernova. Type 1 supernovae originate from white dwarves with carbon-oxygen cores. Type 2 supernovae occur when the iron core of a large star exceeds a certain size. In both cases, the ensuing runaway fusion reaction can create much heavier elements, but it appears that smaller stars don’t necessarily fuse iron before exploding.
That’s a good article. I should’ve checked Wiki first, I guess.
This, though, might become one of my favorite sayings:
Especially considering the username.
Heavier stars are actually the ones which go furthest down the Periodic Table before dying. It’s just that, when they do eventually die, they do so much more dramatically. The lightest stars will never even burn helium, and when the hydrogen runs low (sometime trillions of years hence), they’ll just sort of fade out, not with a bang, but a whimper.
Iron is the limit for productive fusion. Once you get to that point, any further fusion reactions take up more energy than they release*. This creates an energy sink at the center of the star, which means there’s no longer enough heat being given off to support the star’s mass. Supernova time!
When a massive star collapses, the collapse can create a powerful shockwave that will fuse iron even further down the periodic table. This is where all the heavier elements come from. This high-mass fusion gives off energy, but not enough to prevent the star’s collapse.
*Iron is also the limit for fission reactions; any smaller atoms will give off less energy when splitting than it takes to get them to split.