Lives of Low Mass Stars
The battle against the inexorable force of gravity ... lost. Part I.
Low mass stars: less than 2 solar masses. Convective zone + radiative
Intermediate: 2-8 solar masses. Radiative structure
High mass stars: more than 8 solar masses. Convective core + radiative
Where's the bottom of the main sequence?
0.076 solar masses.
Below this mass the core never gets hot enough to fuse H stably.
Why doesn't it collapse?
Degenerate pressure (see White Dwarfs below)
- Slight wobble in motion noted by Bessel, 1834-1844
- Sirius B viewed by Alvan Clark, 1862
- Sirius B hotter than Sirius A but about 10 magnitudes fainter
- Radius of Sirius B is about the same as the Earth
- Mass of Sirius B is about that of the Sun
- Density of Sirius B is about 106
Main Sequence Evolution: Low Mass Stars
- H-burning reduces the number of particles in core, reducing pressure
- temperature increases to compensate
- nuclear reaction rates proportional to temperature, and increase
- luminosity increases with time
- the Faint Young Sun problem
- the real Global warming
When the Sun runs out of fuel
- core contracts and heats up
- H-shell burning
- triple-alpha reaction
- red giants
- Helium flash
- Horizontal Branch
- Planetary nebulae