black-body radiation: planck distribution (rayleigh-jeans, wien distributions) wien’s law
DESCRIPTION
Black-body radiation: Planck distribution (Rayleigh-Jeans, Wien distributions) Wien’s Law Stefan(-Boltzmann) Law. supergiants (I). giants (III). main sequence (V). white dwarfs. Observational HRD may use colour in place of temperature, and magnitude (brightness) in place of luminosity. - PowerPoint PPT PresentationTRANSCRIPT
Black-body radiation:
Planck distribution(Rayleigh-Jeans, Wiendistributions)
Wien’s Law
Stefan(-Boltzmann) Law
Observational HRD may use colour in place of temperature, and magnitude (brightness) in place of luminosity
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
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
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)
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)
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
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??