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But they do leave. Stars not large enough to go supernova do still form planetary nebulas when the more gradually lose their outer layers to space. Only the c
by pfdietz 11mo ago
But they do leave. Stars not large enough to go supernova do still form planetary nebulas when the more gradually lose their outer layers to space. Only the core is left behind to form a white dwarf. This will be the Sun's eventual fate.
- MattPalmer1086 11mo agoWouldn't the heavier elements generally sink to the core and the outer layers be composed of the lighter ones?
- pfdietz 11mo agoNo, gravitational segregation like that is a very slow process and would be overwhelmed by any convection. In Earth's atmosphere, for example, it doesn't occur until very high altitude (80 km or so) where diffusion is fast enough to overcome mixing.
- pfdietz 11mo agoSee also "dredge-up". https://en.wikipedia.org/wiki/Dredge-up https://en.wikipedia.org/wiki/Dredge-up "By definition, during a dredge-up, a convection zone extends all the way from the star's surface down to the layers of material that have undergone fusion."
- MattPalmer1086 11mo agoThat seems to cover elements up to carbon. Not sure heavier elements would be convected?
- pfdietz 11mo ago"The third dredge-up brings helium, carbon, and the s-process products to the surface," (emphasis added) In the early universe, stars had so little in the way of "seeds" for the s-process to act on that the few seeds that were there absorbed large numbers of neutrons, eventually producing weird stars highly enriched in lead (the end point of the s-process). These stars have been detected from lead (and bismuth) in their spectra. https://en.wikipedia.org/wiki/Lead_star https://en.wikipedia.org/wiki/Lead_star
- pixl97 11mo agoI mean it's not hard to do spectrometry on said nebula, and I don't think there is near enough heavier matter detected there.
- pfdietz 11mo agos-process elements (including radioactive ones like technetium) are detected in the spectra of the stars where the process occurs, which means they are right out at the "surface".