Main sequence (core hydrogen burning)

Assembled from 22 blocks · 2 evidence · 24 related

1. Story
2. The long stable phase in which a star fuses hydrogen to helium in its core and the outward pressure of that energy release exactly balances its own gravity. It occupies roughly ninety per cent of a star's luminous lifetime, which is why the main sequence is where most stars are found at any moment and why it appears as a diagonal band rather than a scatter on the Hertzsprung-Russell diagram. Position along the band is set almost entirely by mass: the hot, luminous, short-lived stars sit at the top left and the cool, faint, extremely long-lived ones at the bottom right. The phase is self-regulating - a core that runs slightly hot expands and cools, a core that cools contracts and reheats - and that negative feedback is why a star is stable for billions of years rather than oscillating or exploding. Not a place.
3. Knowledge
4. Main sequence (core hydrogen burning)
5. Red giant and asymptotic giant branch
6. Connections
7. Initial stellar mass
8. Protostar
9. Red giant and asymptotic giant branch
10. Hydrogen fusion: the proton-proton chain and the CNO cycle
11. The Sun
12. Hertzsprung-Russell diagram
13. The Sun forms and settles onto the main sequence
14. Hertzsprung and Russell independently plot luminosity against temperature
15. Main sequence (core hydrogen burning)
16. Betelgeuse (Alpha Orionis)
17. Planetary nebula
18. White dwarf
19. Betelgeuse fades by more than a magnitude
20. Evidence
21. Supports the description of the main sequence as a mass-ordered band and the 1911/1913 attribution and naming history of the Hertzsprung-Russell diagram. Institutional educational material, read via search summary rather than fetched; not a substitute for the original Hertzsprung and Russell publications.
22. Supports general stellar-physics statements in this pack: mass-luminosity scaling, main-sequence lifetimes, degeneracy support and the conventional 1.4 solar mass Chandrasekhar value. This is university-maintained educational reference material, not primary literature, and it was read via search summary rather than fetched. Primary citations should replace it for any figure a reader might quote.