Lecture 16: Overview of Stellar Evolution

"Begin at the beginning. Proceed straight to the end, and then stop."
Louis Carroll

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Date: March 28, 1995
Reading Assignment: pp. 433-519 (review)

Description : review of Stellar Evolution, including binary stars and clusters

Objectives

be able to describe the basic steps in the formation of stars

be able to describe the evolution of a one solar mass star from the Main Sequence to the White Dwarf Stage

be able to describe the evolution of a 10 solar mass star from the main sequence to the formation of a Neutron Star

be able to describe the formation of a Black Hole

be able to describe what happens to White Dwarfs, Neutron Stars, and Black Holes when they are in binary systems

be able to describe the differences between White Dwarfs, Neutron Stars, and Black Holes

be able to describe how binary stars can change the course of stellar evolution

be able to distinguish between Open Clusters and Globular clusters

Lecture Outline

Slide # 1: Overview of Stellar Evolution Slide # 2: The HR Diagram (GRAPHICS)

10 Million Years

Slide # 3: The HR Diagram (GRAPHICS)

10 Million Years

Slide # 4: The HR Diagram (GRAPHICS)

100 Million Years

Slide # 5: The HR Diagram (GRAPHICS)

100 Million Years

Slide # 6: The HR Diagram (GRAPHICS)

1 Billion Years

Slide # 7: The HR Diagram (GRAPHICS)

1 Billion Years

Slide # 8: The HR Diagram (GRAPHICS)

10 Billion Years

Slide # 9: The HR Diagram (GRAPHICS)

10 Billion Years

Slide # 10: The HR Diagram (GRAPHICS)

10 Billion Years

Slide # 11: Blue Stragglers

Stars which are too young to be an normal part of the star cluster

Slide # 12: Binary Star Evolution

stars in binary systems can evolve differently than isolated stars

mass can be transferred between stars in close binary systems

Slide # 13: Binary Star Types (GRAPHICS)

resolved binary system

Slide # 14: Binary Star Types (GRAPHICS)

spectroscopic binary

Slide # 15: Binary Star Types (GRAPHICS)

spectroscopic binary

Slide # 16: Spectroscopic Binaries

found by examining spectrum

two different stellar spectra observed

Doppler shifts from orbital motion can be detected in many causes

Slide # 17: Eclipsing Binary

binary stars can eclipse each other

orbits aligned so one star passes in front of the other

the total amount of light from the stars varies because of the eclipses

Slide # 18: Binary Star Types (GRAPHICS)

Eclipsing Binary Stars

Slide # 19: Eclipsing Binary (GRAPHICS)

Light Curve

Slide # 20: Mass Transfer

mass can be transferred between stars in binary systems

Slide # 21: Evolution of Stars (GRAPHICS)

binary stars system - main sequence

Star A - blue star = 4 solar masses

Star B- red star = 0.5 solar masses

Slide # 22: Binary Star Evolution (GRAPHICS)

Star A becomes a red giant

very low surface gravity and density

massive stars evolve more rapidly

some mass is captured by the 0.5 solar mass star

Slide # 23: Binary Star Evolution (GRAPHICS)

Star A remains a red giant, but has a lower mass

Star B gains lots of hydrogen rich material

spectral class changes to a bluer star

Slide # 24: Binary Star Evolution (GRAPHICS)

Star A - current mass = 1.0 solar masses

red giant

Star B - current mass = 3.5 solar masses

hot, main sequence star

Slide # 25: The Result

it appears as though a massive star is less evolved than a low mass star

binary stars have much more complex evolution than isolated stars

isolated stars depend only on their initial mass

Slide # 26: Algol

binary star system

star 1 = 3.7 solar mass B8V (main sequence)

star 2 = 0.8 solar mass K8IV (subgiant)

eclipsing binary star system

short orbital period and very close orbits

Slide # 27: Constellation Corner (GRAPHICS)

Constellation De Jour

Slide # 28: Constellations on Test #2

Gemini - Castor and Pollux

Auriga - Capella

Perseus - Algol

Lyra - Vega

Cygnus - Deneb

Aquilla - Altair

Slide # 29: Lyra and Cygnus (GRAPHICS)

Fairfax - May 1 - West - 1am - 4.0

Slide # 30: Lyra and Cygnus (GRAPHICS)

Fairfax - May 1 - East - 1am - 4.0

Slide # 31: Lyra and Cygnus (GRAPHICS)

Fairfax - May 1 - East - 1am - 4.0

Slide # 32: Winter Constellations (GRAPHICS)

Fairfax - 8pm - S - 4.0 - March 5

Slide # 33: Winter Constellations (GRAPHICS)

Fairfax - 8pm - S - 4.0 - March 5

Slide # 34: Looking North (GRAPHICS)

March 6 - 8pm - NW - 4.0 - Fairfax

Slide # 35: Looking North (GRAPHICS)

March 6 - 8pm - NW - 4.0 - Fairfax

Slide # 36: More Binary Star Evolution

White Dwarfs

Neutron Stars

Black Holes

Slide # 37: White Dwarfs in Binary Systems

accretion disks

nova explosions

type I supernova

Slide # 38: Accretion Disks

material forms disk as it is transferred to a compact star

disk emits energy from collisions and compression

possibly more energy than the two stars

Slide # 39: Accretion Disks (GRAPHICS)

mass transferred to a compact star

Slide # 40: Nova (GRAPHICS)

hydrogen rich material compresses and then ignites (nuclear fusion) on the sur

Slide # 41: Type I Supernova

white dwarf mass exceeds Chandarsekhar limit

star collapses and carbon detonation occurs

MUST OCCUR IN A BINARY SYSTEM

does not produce a neutron star

Slide # 42: Type II Supernova

core collapse of SINGLE MASSIVE STAR

core made of degenerate iron

mass of core exceeds Chandrasekhar mass

electrons absorbed into nuclei

no pressure from electrons, so core collapses

very luminous

Slide # 43: Neutron Stars (GRAPHICS)

size comparison

Slide # 44: Neutron Stars

rapid rotation

angular momentum is conserved

rotation rate increases with small size

rotation rate approximate once per second

very high magnetic field

compression increases magnetic field

trillions of times stronger than Earth's

very strong surface gravity

escape velocity close to the speed of light

Slide # 45: Pulsars

magnetic fields only allow EM energy to escape in certain directions

charged particles are trapped by magnetic fields

the rotation causes the magnetic field to rotate

the magnetic field is not aligned with the rotation axis

EM energy appears to pulse because of the rotation

1 pulse approximately every second

Slide # 46: Pulsars (GRAPHICS)

the lighthouse effect

Slide # 47: Binary Pulsars

accretion disks

millisecond pulsars

tests of relativity

discovery of planets?

Slide # 48: Accretion Disks

neutron star have accretion disks

because the surface gravity is stronger, accretion disks are brighter and more

X-ray and gamma ray emission occurs

Slide # 49: Millisecond Pulsars

the accretion disk around a pulsar speeds up its rotation rate

angular momentum added to the pulsar

rotation period is smaller

few milliseconds

nearly fast enough to break up the pulsar

Slide # 50: Tests of Relativity

binary pulsars can have very small orbits

very strong gravity field

accurate clocks (pulsars)

GREAT TESTS OF GENERAL RELATIVITY!

NOBEL PRIZE 1993 in PHYSICS

Slide # 51: Planets around Pulsars

changes in the arrival time of pulses can result from orbits

very small orbital changes can be measured

Slide # 52: Detecting Black Holes

binary star systems

if one star is a black hole and the other is a normal star, you might be able

Cygnus X-1 is a good candidate for a black hole

Slide # 53: Spectroscopy

binary star system with an invisible companion

star #1 = Blue supergiant = 30 solar masses

orbital period = 5.6 days

orbital velocity measured by Doppler shift

gas apparently is flowing to the invisible companion

Slide # 54: Orbital Information

invisible companion must have a mass between 5 and 10 solar masses

too large for a neutron star

Slide # 55: X-ray Observations

X-ray observations require several million degree gas to be near Cygnus X-1

hot gas is creates the X-rays

X-ray variations indicated that size of the object must be less than 300 km

too small to be a normal star

Slide # 56: Are there really black holes?

Yes...

Wallin's odds of black holes being real = 98%

Slide # 57: The HR Diagram (GRAPHICS)

one solar mass star over 8 billion years

Slide # 58: The Helium Flash (GRAPHICS)

two energy sources!

Slide # 59: Core Helium Burning

two energy sources!

Slide # 60: The Steps

gas cloud

fragmentation

protostar

Helmholtz contraction

Hayashi track

ignition

adjustment to the Main Sequence

Slide # 61: The HR Diagram (GRAPHICS)

pre-main sequence

Slide # 62: Post Main Sequence- Internal Changes

core depletion of hydrogen

hydrogen shell burning

helium flash and helium core burning

helium depletion

helium shell burning

helium shell flashes

planetary nebula - white dwarf

Slide # 63: Helium Shell Burning (GRAPHICS)

4 layers in the star

Slide # 64: Post-Main Sequence HR Diagram

subgiant branch

giant branch

horizontal branch

asymptotic giant branch

planetary nebula

white dwarf

Slide # 65: The HR Diagram (GRAPHICS)

one solar mass star over 8 billion years

Slide # 66: The HR Diagram (GRAPHICS)

Why?