Chris Alex wrote: ↑Tue May 30, 2023 5:38 pm
Chris Peterson wrote: ↑Tue May 30, 2023 1:21 pm
MarkEt wrote: ↑Tue May 30, 2023 7:58 am
Seems the outer layers are blown out by the initial collapse, then depending on the mass involved you either get the white dwarf or supernova and black hole following it
Stars that produce planetary nebulas are not massive enough to end in supernovas or to become either neutron stars or black holes. In the last few millennia of their fusing existence very high stellar winds blow off much of their mass, producing what we see as planetary nebulas, typically ionized by the very hot end stage of their fusion or their final stage as a white dwarf.
Planetary nebulae descriptions often leave something vague about the process, I find, namely that the star "sheds" its outer layers. What does shed mean? The layers just detach and float away? What is the actual process? So here you bring a much appreciated precision: stellar winds blow off the layers. So is that the process? While supernovae remnants are formed by a bounce-off of layers, planetary nebulae are formed by winds blowing away layers? (winds that are intensifying as the star contracts maybe?)
I think - think
, mind you, and I'm too lazy to google - that sunlike stars that are at the end of their lives have two fusion processes going. In their core, these stars fuse helium into oxygen and carbon. in a shell around their core, they fuse hydrogen into helium.
But here's the deal: I think that these fusion processes turn on and off, and when one fusion process is on, the other is on hold. This injects spurts of energy into the system instead of creating a "smooth flow of energy" as in the Sun. On-off, on-off, on-off, on-off!!!
this creates an imbalance in the star that causes the star to lose its outer layers. I think that sunlike stars typically lose their outer layers in several stages. Also, when the star has lost a great deal of its outer layers, the stellar wind will get stronger. The reason for this would be that there used to be a perfect balance between the outward-directed energy generated in the star's core and the inward-directed pressure caused by the entire mass of the star. But when the star has shrugged off a considerable amount of its mass, and the energy generated in the core is still the same (or actually greater), then there will be a pretty furious wind blowing from the star's core, and the mass loss will proceed even faster.
Do chime in here, Chris. Ding ding!