Black-body radiation: Planck distribution (Rayleigh-Jeans, Wien distributions) Wien’s Law Stefan(-Boltzmann) Law

giants (III) main sequence (V) supergiants (I) white dwarfs

Observational HRD may use colour in place of temperature, and magnitude (brightness) in place of luminosity

The main proton-proton chain

So, what’s SNU?

Mid -1968: Davis, Bahcall, Homestake mine experiment - only 1/3 of expected high-energy (PP-II, III) neutrinos found 1989, Kamiokande - only 1/2 of expected high-energy neutrinos Early 1990s, GALLEX, SAGE confirmed absence of low-energy neutrinos (important because dominant) Late 1990s, SuperKamiokande precisely confirmed high-energy deficit of mainly electron neutrinos but with some senitivity to other flavours (muon, tau) 2001 June 18 - Sudbury Neutrino Observatory, bigger deficit the SuperKamiokande, for the same energy electron neutrinos (only) 2002, Davis gets Nobel Prize

The solar neutrino problem: neutrino oscillations [the Mikheyev-Smirnov-Wolfenstein (MSW) effect]

In 1967, two years before his epochal paper with Gribov on solar neutrino oscillations was published, Bruno Pontecorvo wrote: "Unfortunately, the weight of the various thermonuclear reactions in the sun, and the central temperature of the sun are insufficiently well known in order to allow a useful comparison of expected and observed solar neutrinos..." In other words, the uncertainties in the solar model are so large that they prevent a useful interpretation of solar neutrino measurements.

Bruno Pontecorvo's view was echoed more than two decades later when in 1990 Howard Georgi and Michael Luke wrote as the opening sentences in a paper on possible particle physics effects in solar neutrino experiments: "Most likely, the solar neutrino problem has nothing to do with particle physics. It is a great triumph that astrophysicists are able to predict the number of 8B neutrinos to within a factor of 2 or 3..." C. N. Yang stated on October 11, 2002, a few days after the awarding of the Nobel Prize in Physics to Ray Davis and Masatoshi Koshiba for the first cosmic detection of neutrinos, that: "I did not believe in neutrino oscillations even after Davis' painstaking work and Bahcall's careful analysis. The oscillations were, I believed, uncalled for."

Web page: http :// Neutrinos: different flavours have different masses Sum of masses: <1eV (?) Differences: O(0.1eV) (?)

The Hertzsprung-Russell Diagram is a plot of Temperature (colour, spectral type) vs Luminosity (brightness) Most (90%) of stars lie on the Main Sequence, where stars burning hydrogen to helium (proton-proton or CNO cycles) are in hydrostatic equilbrium Sun shines through proton-proton reactions, which emit electron neutrinos  ‘Solar Neutrino Problem’  discovery of ‘neutrino oscillations, neutrino mass How do stars get on to the main sequence, and what happens afterwards? – stellar evolution

Giant Molecular Clouds: Radii 50 pc Masses 100,000+ solar masses Temp few 10s of K Densities of order 10 molecules per cubic cm (10**20 smaller than the core of a star…) Collapse to from stars, ca x solar mass

Main-sequence lifetime can be estimated

For 1 solar mass: Main Sequence lifetime: years (ZAMS  TAMS) As 4H  1 He, number of particles falls, pressure drops core contracts core temperature rises  pressure rises  increased luminosity, increased radius (‘Mirror law: shrinking core  expanding envelope!) Temperature rise = 300K 6% increase in radius ZAMS NOW

End of core hydrogen burning  core cools, pressure decreases Cores shrinks  energy deposited in hydrogen burning shell (Kelvin-Helmholtz contraction; core temperature actually increases when fusion stops!) – CNO burning (thin) Luminosity increases, star expands, becomes a Red Giant: burning hydrogen to helium in a shell around a helium core (for about 10% of MS lifetime for a solar-mass star)

giants (III) main sequence (V) supergiants (I) white dwarfs

Hydrogen “ash” falls onto core, which contracts, temperature rises; at 10 8 K core helium burning (triple alpha) starts. Degenerate core: temperature increases but pressure does not!  Helium flash (raises degeneracy) New configuration, core helium burning (+shell hydrogen burning) on the ‘horizontal branch’ (core expands, star contracts), for about 1% of the MS lifetime for a solar-mass star (helium burning goes fast)!

After core helium exhaustion, shell helium burning starts; the star becomes a second type of ‘red giant’: Main Sequence Red Giant Branch Horizontal Branch *Asymptotic Giant Branch (AGB) Helium in shell becomes exhausted Overlying hydrogen shell falls back & reignites  feeds helium shell, compressed, heated  helium shell flash (for degenerate cores)  ‘thermal pulse’ Complicated! But result is an unstable star (a pulsating variable) which loses its outer layers

‘Dredge-up’ – convection brings processed material from core to surface on red-giant branches First: during shell hydrogen burning Second: during shell hydrogen burning (Further dredge-ups possible) Of some personal significance… As the outer layers disperse the carbon-oxygen core (left from core helium burning) is exposed  Planetary Nebula (lifetime ca. 10,000 years, from expansion) + remnant carbon-oxygen white dwarf (electron degenerate)

White dwarf mass-radius relation and the Chandrasekhar Limit

EVOLUTION OF MASSIVE STARS Initial stages (contraction onto MS, core hydrogen burning on MS) broadly similar (Radiation pressure prevents formation of very high masses, >100 solar masses) Higher masses  hotter cores; core H burning is through the CNO cycle AND later stages of `burning’ (beyond triple-alpha burning of helium) are possible at later stages of evolution

For stars > 4 solar masses, carbon-oxygen core is more massive than ‘Chandrasekhar limit’ Electron degeneracy can’t support core, so further heating & burning occurs: Carbon burning  O, Ne, Na, Mg >8 solar masses, neon burning (109K), then oxygen burning, silicon burning, oxygen burning, silicon burning  various products (sulfur—iron) Faster and faster!! (C: few hundred years; Si, a day)

No further fusion processes possible; core collapses; proton & electrons “squeezed” together to form neutrons, emitting neutrino pulse “bounceback”  shock wave through overlying layers (more neutrinos)  core collapse supernova

SN 1987A (LMC)

Review: Low & medium-mass stars: White dwarfs supported by electron degeneracy) 7-20 solar masses Neutron stars (densities of nuclear matter!) >20 solar masses Black holes Are these products observable??