Stars III Stellar Evolution Three kinds of timescales

Three kinds of timescales • The nuclear timescale how long it takes the reservoir

Post-MS evolution The formation and subsequent collapse of condensations in the ISM, the contraction

Evolutionary paths in the HRD up to the point where He burning sets in.

The evolutionary end points of stars with different masses shown as a function of

Homework: Textbook of D. Maoz, P. 108, 1, 9, 10

Slides: 24

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Stars III. Stellar Evolution

Three kinds of timescales • The nuclear timescale how long it takes the reservoir of nuclear energy in the star to be released. (see last section) [main sequence] • Kelvin-Helmholtz timescale (or thermal timescale) how long it takes for thermal energy produced in the center of the star to work its way out via energy transport; or how long the energy release lasts from gravitational contraction. (see last section) • The free-fall timescale (or dynamical timescale) how quickly the star mechanically adjusts to changes.

In units of 10^6 years

Free-fall timescale Maoz p. 32

Post-MS evolution The formation and subsequent collapse of condensations in the ISM, the contraction of protostars towards the MS will be discussed in Section IV.

Evolutionary paths in the HRD up to the point where He burning sets in. The shade of the line segments indicates the time spent in the corresponding phases. MS (1 -3) life-times: 1. 0·MΘ: 9. 0 E 9 yrs 2. 2·MΘ: 5. 0 E 8 yrs 15·MΘ: 1 E 7 yrs GB (5 -6) life-times: 1. 0·MΘ: 1. 0 E 9 yrs 2. 2·MΘ: 3. 8 E 7 yrs 15·MΘ: 1. 5 E 6 yrs (6 -10) Iben 1967, ARAA

Schematically Overview