Presentation on theme: "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."— Presentation transcript:
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 Neutron Star OR Black Hole 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
Slide 2 Protostar Gravitational contraction of space matter. Source of energy is gravity. Starts typically with a size of several light years. (1 ly ~ 10 13 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 4H He + 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 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 14Fig. 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 10 10 to 10 11 times. Often outshines the whole galaxy.
Slide 19Fig. 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 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 24Fig. 13-11a, p.267 Crab nebula remnant of Supernova 1054. Has a pulsar in it.
Slide 25Fig. 13-11b, p.267 Veil nebula supernova exploded 20,000 years ago
Slide 26Fig. 13-12a, p.267 Tycho’s Supernova expanding since 1604