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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 D G I A N T
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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 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 M is mass of the star in units of mass of the Sun M
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. Protostar
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. Main Sequence 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. Red Giant Stars
Betelgeuse in Orion Diameter ~ 100 × of Sun Fig. 13-8a, p.265
Betelgeuse Fig. 13-8b, p.265
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). M is mass of the Sun. Death of Stars
Planetary nebula: Ring Nebula in Lyra p.260
Knots are about 100 AU tails 1,000 AU Helix planetary nebula Fig. 13-1, p.261
Dumbbell planetary nebula Fig. 13-3, p.262
Egg nebula planetary nebula
Size of White Dwarf about planet size. Fig. 13-5, p.263
Sirius B is a white dwarf Fig. 13-6a, p.264
For Red Giants with mass > 4 M core 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. this is where elements heavier than iron are formed. 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. Supernova
AST1608.swf Binding energy. How tightly the protons and neutrons are bound.
Supernova Supernova
Tarantula Nebula in Large Magellanic Cloud (a neighboring galaxy) and 1987A supernova Before and after February 24, 1987 Fig. 13-13, p.268
Rise in brightness very rapid ~ 1 day. Drop in intensity ~ 1 year. On the average 1 supernova per century per galaxy. Last supernova observes in our galaxy was about 400 years ago. Last supernova observed by “naked eye” was in 1987 in Large Magellanic Cloud galaxy. Many supernovae are observed each year in far away galaxies. Supernova
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. Supernova remnants
Crab nebula remnant of Supernova 1054. Has a pulsar in it. Fig. 13-11a, p.267
Veil nebula supernova exploded 20,000 years ago Fig. 13-11b, p.267
Tycho’s Supernova expanding since 1604 Fig. 13-12a, p.267
Cassiopeia supernova remnant Fig. 13-12b, p.267
Size of neutron star Fig. 13-18, p.271
Location of pulsars (neutron stars) Fig. 13-21, p.272
Crab Nebula Pulsar in Xray at maximum and minimum Fig. 13-23, p.274
Binary pulsar perihelion shift due to gravity waves as predicted by Einstein general theory of gravity 4º per year. Fig. 13-26, p.275
