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Stellar Evolution

M<0.08 .08<M<0.4 0.4<M<1.4 1.4<M<~4 M>~4 P R O T O S T A R | M a i n S e q u e n c e

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Stellar Evolution

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  1. M<0.08 .08<M<0.4 0.4<M<1.4 1.4<M<~4 M>~4 P R O T O S T A R | M a i n S e q u e n c e | R E D G I A N T | | | Planetary Supernova | | | Nebula | | W h i t e D w a r f | B r o w n D w a rf Neutron Star OR Black Hole Stellar Evolution M A I N S E Q U E N C E R E D G I A N T W H I T E D W A R F B R O W N D W A R F

  2. Hubble image of gas and dust around a cluster of young, hot stars Fig. 12-1, p.248

  3. Protostar – contracting gas due to gravity. Size ~ 1 ly ~ 1013 km, energy source -- gravity. Main Sequence – normal star. Size ~ 106 km to 107 km, Energy – nuclear fusion 4H  He + energy. 0.7% of mass converted to energy, E = mc². Energy source – nuclear fusion. Next stage – red giant. Size ~100 times Main Sequence. If not enough mass then Brown Dwarf. Energy source – nuclear fusion. Stellar Evolution

  4. Fig. 12-2a, p.248

  5. Main sequence stars Protostar Fig. 12-2b, p.248

  6. Fig. 12-4, p.250

  7. HST Protostar with two jets Fig. 12-5a, p.251

  8. Protostar with Jet Jet Fig. 12-5b, p.251

  9. Protostar with two jets Fig. 12-5c, p.251

  10. Mass of He is less than 4 H. Difference gets converted to energy E = mc². Fig. 12-6, p.252

  11. Fig. 12-8, p.253

  12. Proton - proton chain fusion in main Sequence stars. Does not occur in one step. Also emit photon (γ) and neutrino (ν). Fig. 12-10, p.255

  13. Main Sequence stars. • The star is very stable and continues to produce energy until the • hydrogen in the core gets depleted and hydrogen to helium • fusion stops. • Energy source – Fusion of 4HHe + Energy • The energy production is directly proportional to the mass to the • power ~4 (M4). • Since the supply of energy is proportional to the mass, • then the lifetime of the star in the main sequence mode is • proportional to M (fuel supply)/M4 (fuel use) = 1/M³. • The lifetime of a one solar mass star is 10 billion years (1010 yrs). • Other main sequence star lifetime in main is T = 1010/M³ years, • where M is in units of solar mass. • Since massive stars live a shorter lifetime, it is not surprising that • most of the main sequence star are low mass ones.

  14. Hydrostatic equilibrium in a main sequence star. Gravity is balanced by outflow energy pressure

  15. Brown dwarf If protostar does not have enough mass to start nuclear fusion star contracts to Brown dwarf Brown dwarf Fig. 12-11b, p.256

  16. ν hardly interacts, so it escapes and reaches Earth with the velocity of light or in about 8 minutes. Since ν hardly interacts, ν detectors need to be extremely large. Solar neutrino problem pre 2000 – there are not enough neutrinos to account for the energy of the Sun. Problem solved, ν has a very small mass. Solar Neutrinos (ν)

  17. Homestake Solar neutrino Telescope South Dakota Fig. 12-12, p.256

  18. Water detector for neutrinos (ν) in Japan. Kamiokande Fig. 12-13, p.257

  19. Sudbury Neutrino Observatory in Canada. Fig. 12-14, p.258

  20. Note: Planetary nebula are NOT related to planets. Fig. 12-15, p.258

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