Download HR Diagram of One Solar Mass Evolution

Review – Stellar Evolution
• Main Sequence - star burns hydrogen to helium ion core
• Red Giant – hydrogen burns in shell leaving helium
• Horizontal Branch – helium burns in core leaving carbon
One Solar Mass Star’s Evolution
AGB
HB
Red Giant Branch
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Interior of
Asymptotic Giant •
Branch Star •
All Helium in core burns
to carbon-oxygen
Core contracts beginning
shell Helium fusion
Star becomes a Red Giant
again but this time it is
called Asymptotic Giant
Branch star
• Core spins faster than
envelope from Kepler
asteroseismology data
Asymptotic Giant Branch
• Horizontal Branch (10) to end of Asymptotic Giant (11)
takes 50 million years
• Convection goes deep into star & dredges up Carbon etc.
• Kepler asteroseismology data can now distinguish AGB
from red giant stars
Thermal Pulses
• Helium shell flashes
surrounding the inert carbon
core eject the envelope
• Star can lose half its mass
AGB Stars Enrich Interstellar Medium
• Diagram by, Marengo, M.
Planetary
Nebulae
• M57 the “Ring Nebula” is the
most famous of ~1000
• Originally named Planetary
by W. Herschel in 1790
because they resembled
Uranus which he discovered
Dumbell M27
• Gas ejected by “thermal pulses”
during Helium shell flash
• First planetary nebula discovered
by Messier 1764
Hourglass Nebula
• Emission lines indicate a
low density gas
• And a hot (>25000K)
central star
• Nitrogen red & Hydrogen
green & Oxygen blue
Planetary Nebula - NGC 7027
• Slow wind initially and fast wind later catches it and compresses
Planetary Nebula-NGC 6751
• From apparent size and proper motion the age is 1000’s years
• From expansion velocity of ~10 km/sec the distance is 1000 lightyears
• From distance and apparent size the linear size is ~a light year
Planetary Nebula
• Short lived phase of star’s life yet we see thousands so most stars
must produce planetary nebulae
NGC 2440: Cocoon of a New White Dwarf
• In center of frame is 200,000K temp white dwarf
• Mass loss from solar wind & esp. dust in atmosphere
• 8 Solar masses can become 5 in 500,000 years
Core Becomes White Dwarf
• One Example is Sirius B
• Radius about the Earth’s
• Surface temperature is
25000K
• Mass is ~1 solar mass
• Gravity = 100,000 Earth’s
• Atmosphere very thin
White Dwarfs in M4
• Most stars become white dwarfs
• So there are billions in our galaxy, but they are faint
Cooling Curves
• After formation white dwarf continues to cool – no energy sources
• Coolest “black dwarf” is ~6000K – age of 12 billion years
Density of
Degenerate
Matter
White Dwarf’s density is
3,000kg/cm3
(teaspoon=semi)
Pressure resisting gravity
is given by degenerate
electrons
Compact Objects / Stars
• Small radius & Large mass =
• High density
Mass-Radius
Relation for
White Dwarf
Stars
Chandrasekhar Limit
• An electron degenerate star
can not be more massive than
1.4 solar masses
• Mass loss can be so large that
even 7 or 8 solar mass stars
may become this small
• But what about bigger stars?
Death of an OB Star
Massive Star Evolution
• Electrostatic repulsion (Coulomb barrier) larger for heavy elements
• Higher temperature & pressure is needed to fuse heavy elements
Supergiants
• No degenerate core
• Higher core temperatures burn heavy
elements into heavier elements
• Each element burns more quickly
giving less energy than the last
Nucleosynthesis
Up to Iron
• Other elements fuse/burn
producing energy/heat
• Up to IRON
• Heavier elements
produces less energy
• So burn for a shorter time
8 Solar Mass Star
• Lighter elements burn in cooler
shells farther from core
• Star larger than 8 Msun can’t
lose enough mass to become
white dwarf
• We are all made of star dust
• We are ashes of nuclear
furnaces
• We are nuclear waste
Type II Supernova
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When iron core reaches a few solar masses – dense core collapses
Innermost 500km in a few millisconds (0.25c)
So hot photons photodisintegrate Iron - absorbing energy
Electron +Proton  Neutron + Neutrino & Neutrinos escape
99% of energy comes out as neutrinos, 1% shock wave, 0.01% light
Supernova Explodes
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Neutron degeneracy stops collapse => rebounds
Rebound forms shock wave but it stalls
Density ~1012 gm/cm3 so even neutrinos push shock
Plus turbulence and star explodes
Fritz Zwicky
• Bright as galaxy: TypeIa@6500ly=Venus
@500ly=Moon, @1 light year =Sun
Types of Supernovae
• Type I – No Hydrogen
• Type II – Have
Hydrogen
• Type III – SN 1961I
• Type IV – SN 1961F
Supernovae Classification
Spectra Comparison
• Type Ia – White dwarf
explodes destroying star
• Type II – core-collapse
of massive star leaving
neutron star or black hole
• Type Ib – core collapse
of stripped star
Historical Supernovae
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Year Date Con
1006 Apr 30 Lup
1054 Jul 4 Tau
1181
Cas
1203 ?
Sco
1572 Nov 6 Cas
1604 Oct 9 Oph
1680?1667? Cas
mag Remnant
-9
-6 M1 Crab
-1 3C 58
0 1230? Aql
–4 Tycho SNR
–3 Kepler SNR
? Cas A
Observed/Comments
Arabic; also Chinese, Japanese, European
Chinese, North American(?) Arab, Japan
Chinese and Japanese
Tycho Brahe's SN
Johannes Kepler's SN
Not seen ? Radio remnant 1950
1 supernova per galaxy per 100 years BUT
Not all observed !
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Crab
Guest star appeared 4 July 1054
Seen by Chinese in daytime; distance=6500ly
Red is emission nebula =supernova remnant
Blue is synchrotron emission
Powered by compact object
Nebula
Synchrotron
Radiation
• Electron Spirals in
Magnetic field
• Acceleration causes
emission of photon
• Polarized light
Supernova Remnants
• Expanding shell enriches interstellar
medium with heavy elements
• Debris from Crab=100tons, hits
Earth in 100,000years
Cosmic Elemental Abundances
• Peak at Iron
• Elements beyond iron formed rapidly
by neutron capture during collapse
SN1987A
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In LMC, by Ian Shelton
169,000 light years
Peculiar Type II
Decay of radioactive Nickel and
Cobalt kept it bright for months
Neutrino Detector
• 10 trillion/sec pass through you
• 20 Neutrinos from SN1987A
detected so theory is correct
• Neutrinos arrived hours before
light so neutrino’s speed~=light
• IceCube @ South Pole
Are Supernovae Dangerous?
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Type II=Spica, Rigel, Betelguese not close
IK Peg Type Ia progenitor
Initial burst of light, neutrinos, okay but
X-rays & Gamma-rays=ozone layer destruction
Dangerous within ~10 pc
Past
Extinctions
• Extinction every 100?
Million years
• Past extinctions? –
maybe evidence from
sea floor&ice caps
Earth-like Planet?
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GL 667C M2V: triple system: 22 light years distant
Planet is 5 Earth Masses
Orbits in 28days= Middle of habitable zone
So close there must be lots of similar planets
Lagrange 1736-1813
• One of the greatest mathematicians of
the 18th century
• Survived the French Revolution
• Newton solved two body problem
• Lagrange solved restricted three body
problem
Lagrange Points
• Lagrange Points are where gravitational forces of two stars balance
• L1, L2, L3 are unstable but L4&L5 are stable
• SOHO at L1 and at L2 is WMAP and maybe JWST
Roche Lobes
• Roche Lobes are the
regions of gravitational
influence of each star
• Close Binary stars have
a different evolution
• If the star fills Roche
Lobe then it will
overflow onto
companion
Mass Transfer
• Massive star makes big dent and small star makes small dent
• When more massive star becomes red giant
• It overflows its Roche lobe transfers mass through L1 point
Semidetached binary
• Can peel off outer layers of star and transfer them to the companion
• Algol paradox: 5Msun is on Main Sequence and 1Msun is a red giant
Contact Binary
• Two stars can touch
• Overflow = Overcontact
• Forming Blue Straggler Or Rapidly rotating giant
Accretion Disk
• Hydrogen gas flows through L1 but
• Due to angular momentum the gas forms
• Accretion disk first: then falls on star
Hot Spot
• Hot spot forms where
stream hits accretion disk
• Friction in accretion disk
heats gas up to ~million K
• Emitting X-rays
Binary Star Evolution
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Higher mass star evolves first
Forming white dwarf
Companion star becomes a red giant
Overflows its Roche Lobe
Dumping Hydrogen onto white dwarf
Nova
• What happens to the Hydrogen
which falls on a electron
degenerate white dwarf??
Nova 2
• Do not throw gasoline on hot coals!
This  fmjk  
GK Persi
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After ~100 earth masses, burns hydrogen to helium
Nebula ejected at ~600km/sec
0.001 solar mass ejected so white dwarf is not destroyed
We observe a few novae per year in galaxy
Recurrent Nova T Pyx
• Nova can happen again every few to thousands of years
Novae Light
Curves
• Distance Indicators
• Depending on rate
of decline absolute
magnitudes ~-4
Thermonuclear Supernova
• Mass transfer forces white dwarf to exceed (Chandrasekhar?)
limit & collapse triggers carbon deflagration=Type Ia
Debris Enrich Next Generation
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Tycho’s SNR 1572
High, medium and low energy x-rays are blue, green and red
Debris are red yellow green at~10Million K
Material ejected at ~15,000 km/sec creates shock wave
Spectra of light echo gives Type Ia
Animation of
Tycho’s Supernova
• “Runaway star” is found
moving away from center of
nebula at 3 times speed of
other stars ~ 140km/sec
Type Ia
Supernovae
Light Curves
• After correcting for the
stretch/width
• All Type Ia supernovae
have the same intrinsic
brightness
• Same absolute magnitude
Most Distant Supernova
• Because they can become
as bright as a whole galaxy
of stars
• We can find their distance
• Even when they are on the
other side of the universe
Galactic Habitable Zone
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Red zone has too many supernovae
Blue has too few supernovae=heavy elements
Green is just right
Each time step is 600 million years from beginning
of Milky Way until today (12Billion years)
Type Ia
Supernova
• White dwarf in a
binary system
• Which is heated to
ignition by mass
transfer from
secondary
• Heat ignites
carbon
deflagration
• Producing Iron,
silicon etc.
Asymptotic Giant Branch Stars
• Envelope unstable and is ejected relatively gently
Death of a Sun-like Star 0.4-4 Msun
SN1993J in M81in Visible and Radio
• 11 Million ly distant Type IIb
• Reached V=10 so Absolute
Magnitude is ~-18
• Equals a galaxy of stars
• Expansion of nebula and size give
estimate of age ~1000’s years
• Velocity of expansion (10,000
km/sec) & proper motion gives
distance
Supernova Cosmology Project
Supernovae in Spirals and Ellipticals
• Supernova in M51 V=8
• Supernovae Type I found in
spiral and elliptical galaxies
• Supernovae Type II found
only in spiral galaxies near
young stars
Supernova Animation
Nova Herculis 1934
• Hydrogen accretes onto white dwarf = degenerate gas
• After ~100 earth masses
• PP then CNO cycles burn hydrogen to helium