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A stellar core is the extremely hot, dense region at the center of a star. For an ordinary main sequence star, the core region is the volume where the temperature and pressure conditions allow for energy production through thermonuclear fusion of hydrogen into helium.
There are other highly evolved hot stars not generally referred to as blue giants: Wolf–Rayet stars, highly luminous and distinguished by their extreme temperatures and prominent helium and nitrogen emission lines; post-AGB stars forming planetary nebulae, similar to Wolf–Rayet stars but smaller and less massive; blue stragglers, uncommon ...
After a star has consumed the helium at the core, hydrogen and helium fusion continues in shells around a hot core of carbon and oxygen. The star follows the asymptotic giant branch on the Hertzsprung–Russell diagram, paralleling the original red-giant evolution, but with even faster energy generation (which lasts for a shorter time). [18]
Because they are so massive, O-type stars have very hot cores and burn through their hydrogen fuel very quickly, so they are the first stars to leave the main sequence. When the MKK classification scheme was first described in 1943, the only subtypes of class O used were O5 to O9.5. [72]
Cooler stars with higher tidal dissipation damps the obliquity (explaining why hot Jupiters orbiting cooler stars are well aligned) while hotter stars do not damp the obliquity (explaining the observed misalignment). [5] Another hypothesis is that the host star sometimes changes rotation early in its evolution, rather than the orbit changing. [40]
A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant.They are usually considered to be those with luminosity class I and spectral class B9 or earlier, [1] although sometimes A-class supergiants are also deemed blue supergiants.
If the mass of a main-sequence star is between 0.5 and 8 M ☉, [131] [138] its core will become sufficiently hot to fuse helium into carbon and oxygen via the triple-alpha process, but it will never become sufficiently hot to fuse carbon into neon. Near the end of the period in which it undergoes fusion reactions, such a star will have a ...
In the most massive stars, the convection zone may reach all the way from the core to the surface. [2] In main sequence stars of less than about 1.3 solar masses, the outer envelope of the star contains a region where partial ionization of hydrogen and helium raises the heat capacity.