Black-body radiation:

Planck distribution(Rayleigh-Jeans, Wiendistributions)

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 :// www.star.ucl.ac.uk/~idh/1B23

Neutrinos: different flavours have different masses

Sum of masses: <1eV (?)

Differences: O(0.1eV) (?)

The Hertzsprung-Russell Diagram is a plot ofTemperature (colour, spectral type) vsLuminosity (brightness)

Most (90%) of stars lie on the Main Sequence, where starsburning hydrogen to helium (proton-proton or CNO cycles)are in hydrostatic equilbrium

Sun shines through proton-proton reactions, which emitelectron neutrinos ‘Solar Neutrino Problem’ discovery of ‘neutrino oscillations, neutrino mass

How do stars get on to the main sequence, and what happensafterwards? – stellar evolution

Giant Molecular Clouds:

Radii 50 pcMasses 100,000+ solar massesTemp few 10s of KDensities of order 10 molecules per cubic cm (10**20 smaller than the core of a star…)

Collapse to from stars, ca. 0.1-100x solar mass

Main-sequence lifetime can be estimated

For 1 solar mass:

Main Sequence lifetime: 1010 years (ZAMSTAMS)

As 4H 1 He, number of particles falls,pressure dropscore contractscore 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 about10% of MS lifetime fora solar-mass star)

giants (III)main sequence (V)

supergiants (I)

white dwarfs

Hydrogen “ash” falls onto core, which contracts, temperature rises; at 108 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 hydrogenburning) on the ‘horizontal branch’ (core expands, star contracts), for about 1% of the MS lifetime for a solar-massstar (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 exhaustedOverlying hydrogen shell falls back & reignites feeds helium shell, compressed, heated helium shell flash (for degeneratecores) ‘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 burningSecond: during shell hydrogen burning(Further dredge-ups possible)

Of some personal significance…

As the outer layers disperse the carbon-oxygen core (leftfrom 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 burningon 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 burningof 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 furtherheating & burning occurs:

Carbon burning O, Ne, Na, Mg

>8 solar masses, neon burning (109K),

then oxygen burning, silicon burning, oxygen burning,silicon burningvarious 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)

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??