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30.2 Stellar Evolution Stellar Evolution Section 30.2 Hertzsprung-Russell Diagram · Hertzsprung & Russell noticed that the higher a star's temperature, the more energy it gave off per second (luminosity) · developed a graph to show the relationship · most stars fit in a diagonal band that runs from the upper left (hot, blue, bright stars) to the lower right (cool, red, dim stars) called the main sequence 90% of all stars are main sequence stars Hertzsprung-Russell Diagram · white dwarfs small, hot, dim · red giants large, cool · red supergiants largest, cool stars 2 According to the diagram, what are the characteristics of Sirius B? A bright, hot B bright, cool C dim, hot D dim, cool 1 Use the H-R Diagram to determine which star is the hottest and brightest. A Sirius B B Spica C Sirius D Proxima Centauri Star Formation · nebula - beginning of a star cloud of gas and dust that was once in other stars gravity pulls particles closer together and the nebula condenses · protostar - star fetus temperature increases · nuclear fusion makes the birth of a star 30.2 Stellar Evolution Stellar Equilibrium · gravity pushes in · fusion produces heat and pressure that push out · in = out and stars are able to maintain a stable size not true in later life 3 What event marks the birth of a star? A stellar equilibrium B nuclear fusion ends C supernova explosion D nuclear fusion begins Giant vs. Supergiant · 3rd stage · almost all hydrogen has been turned into helium · stars starts to collapse increases the core temperature hydrogen fusion causes the star to expand rapidly stars begin to cool · sun-like stars become red giants · stars bigger than the sun become red supergiants Main-Sequence Stage · 2nd and longest stage · nuclear fusion of hydrogen into helium produces energy · when fusion slows or stops, stars move off the main sequence · next stage is determined by a star's size 4 How do main sequence stars generate energy? A nuclear fusion; helium to hydrogen B nuclear fusion; carbon to hydrogen C nuclear fusion; hydrogen to carbon D nuclear fusion; hydrogen to helium Final Stages of Sun-like Stars · planetary nebula cloud of gas around a star that is dying · white dwarf small, hot, dim star that is the leftover center of an old star becomes a black dwarf when it stops emitting light end of many sun-like stars 30.2 Stellar Evolution · nova Nova vs. Supernova star that suddenly becomes brighter captures gases from a nearby red giant increasing the pressure inside a white dwarf and causes an explosion can be a nova several times Sun-like Star Evolution Summary · nebula protostar sun-like star planetary nebula white dwarf red giant some go through nova/supernova stage most become black dwarfs and disappear · supernova violent explosions that destroy the white dwarf and much of the red giant 5 A large, bright star whose hot core has used up most of its hydrogen is a A giant B nova C supernova D planetary nebula Final Stages of Massive Stars · massive = 8 or more times bigger than the sun · supernovas next step: neutron star or black hole · neutron star - very small but incredibly dense ball of neutrons pulsars - neutron stars that emit radio waves · black hole - an object so massive and dense that even light cannot escape its gravity 6 What is the lifecycle of a sun-like star? 1 - nebula 2 - planetary nebula 3 - protostar 4 - red giant 5 - sun-like star 6 - white dwarf Massive Star Evolution Summary · nebula protostar massive star red supergiant supernova neutron star or black hole 30.2 Stellar Evolution 7 MATA: After massive stars become supernovas they turn into A white dwarfs B neutron stars C black holes D black dwarfs