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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
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

slide2

Hubble image of gas and dust

around a cluster of young,

hot stars

Fig. 12-1, p.248

stellar evolution1
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
slide5

Main sequence stars

Protostar

Fig. 12-2b, p.248

slide8

Protostar with Jet

Jet

Fig. 12-5b, p.251

slide9

Protostar with two jets

Fig. 12-5c, p.251

slide10

Mass of He is

less than 4 H.

Difference gets

converted to

energy E = mc².

Fig. 12-6, p.252

slide12

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

slide13

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.
slide14

Hydrostatic

equilibrium

in a main

sequence star.

Gravity is

balanced by

outflow energy

pressure

slide15

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

solar neutrinos
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)
slide17

Homestake

Solar neutrino

Telescope

South Dakota

Fig. 12-12, p.256

slide18

Water detector for

neutrinos (ν) in

Japan.

Kamiokande

Fig. 12-13, p.257

slide19

Sudbury

Neutrino

Observatory

in Canada.

Fig. 12-14, p.258

slide20

Note: Planetary

nebula are NOT

related to

planets.

Fig. 12-15, p.258

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