[quote=Ann post_id=298373 time=1577947186 user_id=129702]
[quote=BDanielMayfield post_id=298371 time=1577945199 user_id=139536]
[quote]Betelgeuse is also recognized as a nearby red supergiant star that will end its life in a core collapse supernova explosion sometime in the next 1,000 years, though that cosmic cataclysm will take place a safe 700 light-years or so from our fair planet.[/quote]
Is that 1,000 years figure a mistake? Yesterday's discussion indicated sometime in the next 100,000 years.[/quote]
The 1,000 years figure is definitely a mistake! Yes, Betelgeuse [b][i]could[/i][/b] go in 1,000 years. Heck, it could go tomorrow, for all we know.
But it might just as easily last for another 100,000 years, or maybe even longer. After all, it is the condition of the core of Betelgeuse that determines when it will explode. And the core of any star is hidden from us behind thick opaque gases. The reason why the gases are opaque is that the photons from the core keep scattering off electrons and atomic nuclei on their way to the surface of the star.[/quote]
[list]You are right about the 1,000 years figure, Ann.
However, red giants don't have much of a radiative zone
and core/burning shell changes may not take 171,000 years to signal us.[/list]
[quote=https://en.wikipedia.org/wiki/Radiation_zone]
<<A radiation zone, or radiative region is a layer of a star's interior where energy is primarily transported toward the exterior by means of radiative diffusion and thermal conduction, rather than by convection. Energy travels through the radiation zone in the form of electromagnetic radiation as photons. Matter in a radiation zone is so dense that photons can travel only a short distance before they are absorbed or scattered by another particle, gradually shifting to longer wavelength as they do so. For this reason, it takes an average of 171,000 years for gamma rays from the core of the Sun to leave the radiation zone. Over this range, the temperature of the plasma drops from 15 million K near the core down to 1.5 million K at the base of the convection zone.>>[/quote]
[quote=https://en.wikipedia.org/wiki/Convection_zone]
[float=left][img3=An illustration of the structure of the Sun and a red giant star, showing their convective zones. These are the granular zones in the outer layers of the stars.]https://upload.wikimedia.org/wikipedia/commons/thumb/c/c3/Structure_of_Stars_%28artist%E2%80%99s_impression%29.jpg/1280px-Structure_of_Stars_%28artist%E2%80%99s_impression%29.jpg[/img3][/float]
<<A convection zone, convective zone or convective region of a star is a layer which is unstable to convection. Energy is primarily or partially transported by convection in such a region. In a radiation zone, energy is transported by radiation and conduction.
Stellar convection consists of mass movement of plasma within the star which usually forms a circular convection current with the heated plasma ascending and the cooled plasma descending.
If the temperature gradient is steep enough (i. e. the temperature changes rapidly with distance from the center of the star), or if the gas has a very high heat capacity (i. e. its temperature changes relatively slowly as it expands) then the rising parcel of gas will remain warmer and less dense than its new surroundings even after expanding and cooling. Its buoyancy will then cause it to continue to rise. The region of the star in which this happens is the convection zone.
[b][color=#FF0000]In the most massive stars, the convection zone may reach all the way from the core to the surface.[/color] In red giant stars, and particularly during the asymptotic giant branch phase, the surface convection zone varies in depth during the phases of shell burning. This causes dredge-up events, short-lived very deep convection zones that transport fusion products to the surface of the star.[/b]>>[/quote]