de 1 Stellar Evolution 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 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 r f Neutron Star OR Black Hole M A I N S E Q U E N C E R E D G I A N W H I T E D W A R F R O W N D W A R F M is mass of the star in units of mass of the Sun
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Slide 1 Stellar Evolution M ~4 P R O T O S T A R M a i n S e q u e n c 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 r f.
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Slide 1
Stellar EvolutionStellar 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
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 r f Neutron Star OR
Black Hole
M A I N S E Q U E N C ER 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
M is mass of the star in units of mass of the Sun M
Slide 2
Protostar
• Gravitational contraction of space matter.
• Source of energy is gravity.
• Starts typically with a size of several light years. (1 ly ~ 1013 km.)
• Many gravitational contraction points
• When protostar core gets hot enough to start nuclear fusion, a normal star is born.
Slide 3
Main Sequence Stars
• Source of energy is nuclear fusion
• 4 H He + energy as helium mass is less than 4H by 0.7%.
• Star very stable with gravity pulling in and heat energy pushing out.
• The more massive the star, the faster it uses hydrogen.
Slide 4
Red Giant Stars
• After core hydrogen is depleted, core contracts, heats up more and when temperature reaches 100,000,000ºK, 3He C + energy fusion starts.
• Outside of the core the temperature is now over 1,000,000ºK and there is plenty of hydrogen and 4HHe + energy production starts.
• Now more energy is produced, so star expands to about 100 times original size.
• Sun will become a red giant in about 5 billion years, swell about 100 times in diameter and absorb Mercury, Venus and Earth.
Slide 5
Red Giant stars
Slide 6 Fig. 13-8a, p.265
Betelgeuse in Orion
Slide 7 Fig. 13-8b, p.265
Betelgeuse
Slide 8
Death of Stars
• Depends on mass.
• For stars < 4M after all nuclear fusion has stopped, the star collapses into white dwarf, the size of Earth.
• If mass > 1.4 M during collapse the outer layers are expelled and become planetary nebula (nothing to do with planets).
Slide 9 p.260
Ring Nebula in Lyra
Slide 10 Fig. 13-1, p.261
Helix planetary nebula
Knots areabout 100 AUtails 1,000 AU
Slide 11 Fig. 13-3, p.262
Dumbbellplanetarynebula
Slide 12
Egg nebulaplanetary nebula
Slide 13 Fig. 13-5, p.263
Slide 14 Fig. 13-6a, p.264
Sirius B is a white dwarf
Slide 15
Supernova
• For Red Giants with mass > 4 M becomes iron. Iron cannot fuse to higher mass elements and fusion stops and star starts collapsing.
• During the collapse all the outer layers become extremely hot and nuclear fusion starts everywhere except in the core.
• The star explodes into a supernova and the core squeezes into a neutron star or black hole.
• During supernova the star brightens 1010 to 1011 times. Often outshines the whole galaxy.
Slide 16
AST1605.swf
Slide 17
AST1608.swf
Slide 18
Supernova
Supernova
Slide 19 Fig. 13-13, p.268
Tarantula Nebula in Large Magellanic Cloud (a neighboring galaxy)and 1987A supernova
Before and after February 24, 1987
Slide 20
Supernova• Rise in brightness very rapid ~ 1 day.• Drop in intensity ~ 1 year.• On the average 2 supernova per century per galaxy.• Last supernova observes in our galaxy was about 400
years ago.• Last supernova observed in “naked eye” was in 1987
in Large Magellanic Cloud galaxy.• Many supernovae are observed each year in far away
galaxies.
Slide 21
AST1609.swf
Slide 22 Fig. 13-9, p.266
Slide 23
Supernova remnants
• 80% to 90% of the star blows out.• Core squeezes into a neutron star or black
hole.• Neutron star is the size of a city, spins very
rapidly and emits pulses that gave the original name of pulsars.
• If the mass of neutron star is too large, it becomes a black hole.
Slide 24 Fig. 13-11a, p.267
Crab nebularemnant ofSupernova 1054.Has a pulsarin it.
Slide 25 Fig. 13-11b, p.267
Veil nebulasupernovaexploded20,000 yearsago
Slide 26 Fig. 13-12a, p.267
Tycho’sSupernovaexpandingsince 1604
Slide 27 Fig. 13-12b, p.267
Cassiopeia supernova remnant
Slide 28 Fig. 13-18, p.271
Size ofneutronstar
Slide 29 Fig. 13-20a, p.272
Slide 30 Fig. 13-21, p.272
Location of pulsars (neutron stars)
Slide 31 Fig. 13-22, p.273
Slide 32 Fig. 13-23, p.274
CrabNebula Pulsarin Xrayat maximumand minimum
Slide 33 Fig. 13-26, p.275
Binary pulsarperihelionshift due togravity wavesas predictedby Einsteingeneral theoryof gravity