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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 • 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 • • • • • 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 • • • • 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 • • • • • • • • 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 ! • • • • • 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 • • • • 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? • • • • • 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? • • • • 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 • • • • • 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 fmjk GK Persi • • • • 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 • • • • • 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 • • • • 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