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Stellar Evolution. Chapter 12. Think, Pair, Share. Our sun started out as a: Protostar Class G star Neutron star Red giant star. Which stars are the most prevalent in the universe? Which are the least? How do stars sustain their fusion?
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Stellar Evolution Chapter 12
Think, Pair, Share • Our sun started out as a: • Protostar • Class G star • Neutron star • Red giant star
Which stars are the most prevalent in the universe? Which are the least? • How do stars sustain their fusion? • What determines the path that a star takes with its life span?
The Radii of Stars in the Hertzsprung-Russell Diagram 0 Betelgeuse Rigel 10,000 times the sun’s radius Polaris 100 times the sun’s radius Sun As large as the sun
A Census of the Stars 0 • Faint, _____ dwarfs (low mass) are the most __________stars. • Bright, hot, ______main-sequence stars (high-mass) are very _________ • _______and __________are extremely ____.
Heating By Contraction 0 As a _______contracts, it heats up: Free-fall contraction → Heating
Think, Pair, Share • The defining factor that determines its end path (black hole, neutron, white dwarf) a star will take is: • Temperature • Size • Mass • Color
Role of Mass • A star’s ________determines its core ___________and __________. • High-_______stars with >8MSun have _______lives, eventually becoming hot enough to make _____, and end in _______________explosions • Low-______stars with <2MSun have ______lives, never become hot enough to fuse _______nuclei, and end as _______dwarfs • Intermediate ______stars can make elements heavier than ________but end as _________dwarfs
Two forces balance each other: Pressure = Gravity ________________equilibrium: Radiation energy produced at ______creates an ___________force against the ____________force which pushes ___
Four Laws of Stellar Structure • Hydrostatic equilibrium • Energy transport—Energy moves from ____to _____by radiation, convection or conduction • Conservation of mass—Total mass of star _______the sum of the __________of gases • Conservation of energy—Total luminosity ________the sum of energy ___________from each layer of gas.
The End of a Star’s Life 0 • When all the __________fuel in a star is used up, ________will win over __________and the star will _____. • High-mass stars will die _______, in a gigantic explosion, called a ___________. Less massive stars will die in a less _________event, called a _________
Red Dwarfs 0 • Stars with less than ~ 0.4 solar masses are completely __________. Mass • Hydrogen and helium remain well __________throughout the __________star. • No phase of shell “___________”with expansion to ________. • Not _______enough to __________He burning.
Sun-like Stars 0 • Sunlike stars (~ 0.4 – 4 solar masses) develop a ___________core. Mass • Expansion to _____giant during Hydrogen __________shell phase • Ignition of He _____________in the He core • Formation of a _____________C,O core
Degenerate Matter • Matter in the He _____has no _________source left. • Thermal ________is not enough to resist and balance __________ • Matter assumes a new ________, called ________________matter: • Pressure in ____________core has electrons that can _____be packed arbitrarily ___________together and have small ____________.
The Deaths of Massive Stars: _____________ 0 Final stages of ________in high-mass stars (> 8 Msun), leading to the formation of an ______core, happen extremely ___________: ______burning lasts only for ~ ___day. _________core ultimately ___________, triggering an explosion that destroys the star: A ________________
White Dwarfs 0 • ____________________stellar remnant (C,O core) • Extremely dense:__teaspoon of WD material: mass ≈ ____tons!!! • Chunk of WD material the size of a ______ball would outweigh an ________liner! White Dwarfs: Mass ~ Msun Temp. ~ 25,000 K Luminosity ~ 0.01 Lsun
Think, Pair Share • The most massive end to a star’s life would be: • A black hole • A neutron star • A white dwarf
Black Holes 0 Just like ________dwarfs (Chandrasekhar limit: 1.4 Msun), there is a mass _______for _________stars: _________stars can not exist with masses > 3 Msun We know of no mechanism to halt the ____________of a ____________object with > 3 Msun. It will collapse into a _____________point – a ____________: => A Black Hole!
