Stellar EvolutionChapter 12

Think, Pair, ShareOur sun started out as a:

1. Protostar 2. Class G star3. Neutron star4. 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

10,000 times the sun’s radius100 times

the sun’s radius

As large as the sun

Rigel Betelgeuse

Sun

Polaris

A Census of the Stars• Faint, _____ dwarfs

(low mass) are the most __________stars.

• _______and __________are extremely ____.

• Bright, hot, ______main-sequence stars (high-mass) are very _________

Heating By ContractionAs a _______contracts, it heats up:

Free-fall contraction→ Heating

Think, Pair, ShareThe defining factor that determines its end path

(black hole, neutron, white dwarf) a star will take is:1. Temperature2. Size3. Mass4. 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

________________equilibrium:

Radiation energy produced at ______creates an ___________force against the ____________force which pushes ___

Two forces balance each other: Pressure = Gravity

Four Laws of Stellar Structure

1. Hydrostatic equilibrium2. Energy transport—Energy moves from ____to

_____by radiation, convection or conduction3. Conservation of mass—Total mass of star

_______the sum of the __________of gases4. Conservation of energy—Total luminosity

________the sum of energy ___________from each layer of gas.

The End of a Star’s Life• 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• Stars with

less than ~ 0.4 solar masses are completely __________.

• Hydrogen and helium remain well __________throughout the __________star.

• No phase of shell “___________” with expansion to ________.

• Not _______enough to __________He burning.

Mass

Sun-like Stars

• Sunlike stars (~ 0.4 – 4 solar masses) develop a ___________core.

• Expansion to _____giant during Hydrogen __________shell phase

• Ignition of He _____________in the He core• Formation of a _____________C,O core

Mass

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: _____________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• ____________________stellar remnant (C,O core)• Extremely dense:

__teaspoon of WD material: mass ≈ ____tons!!!

White Dwarfs:Mass ~ Msun

Temp. ~ 25,000 KLuminosity ~ 0.01

Lsun

• Chunk of WD material the size of a ______ball would outweigh an ________liner!

Think, Pair ShareThe most massive end to a star’s life would be:

1. A black hole2. A neutron star3. A white dwarf

Formation of Neutron Stars

Black HolesJust like ________dwarfs (Chandrasekhar limit:

1.4 Msun), there is a mass _______for _________stars:

_________stars can not exist with masses > 3

MsunWe know of no mechanism to halt the

____________of a ____________object with > 3 Msun.

It will collapse into a _____________point – a ____________:

=> A Black Hole!