BB 1,2 H 3,4 He 7 Li Intergalactic medium Interstellar medium Galaxy formation inflowGal. winds,...
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Transcript of BB 1,2 H 3,4 He 7 Li Intergalactic medium Interstellar medium Galaxy formation inflowGal. winds,...
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BB1,2H 3,4He 7Li
Intergalactic medium
Interstellar medium
Galaxy formation inflow Gal. winds, stripping, mergers
Cosmic rays
Small stars D, Li
Middling stars
Big stars
Star formation
Spallation 6Li, Be, B
WD NS BH
SN
Explosive r-process
Winds, PN, Novae He, 7Li, C, N
D, Li, Be, B
?
Nucleosynthesis Flowchart
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Lecture 9: Supernova RatesStar-Formation Efficiency, Yield
How many supernovae per year for each galaxy type ?
Use power-law IMF, Salpeter slope -7/3 = -2.33
.
.Limits of validity, not well known
20 M0.1 M8 M
slope = -7/3 = -2.33
Supernova limit
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“Universal” IMF (Kroupa 2002)
log( M / M )
MW MC GC local
log( M / M)
M42 M35 Pleiades local ~ - 7/3 M > 1 M
- 4/3 0.1 - 1 M
- 1/3 M < 0.1 M
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Number of stars :
Fraction of stars with M > 8 M ( for B = -7/3 )
500 stars --> 1 supernova!
Most stars at low-mass end!
Integrating a Power-Law IMF
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Supernovae are rare, but each is very massive.
What fraction of the mass goes into SNe?
Most of mass is in low-mass stars.
SN Mass Fraction
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Median mass:
Mean mass:
.
“Typical” SN Mass
.
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Spiral Galaxy: SFR: ~ 8 M yr-1. 7.2% have M > 8 M .
(8 M yr-1) x 0.072 ~ 0.6 M yr-1 go into SNe
SN rate:
(fewer seen due to dust)
Irregular Galaxy: ~10x this rate during bursts (1 SN per 2 yr)!
No SNe between bursts.
.
.
SN Rates vs Galaxy Type
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SN Rates: Ellipticalst* = 1 Gyr e-folding time
t = 10 Gyr age= 0.95 efficiencyM0 = 1011 M total mass = initial gas massGas consumption:
Star formation:
SN rate:
3 SN per 105 yr. Negligible!
..
..
gas
stars
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What Star Formation Efficiency and Yields of H, He and Metals ?
X = 0.75Y = 0.25Z = 0.00
X = ?Y = ?Z = ?
MG = M0
MS = 0
MG = 0MS = M0
MG = (1-) M0
MS = M0
= ?
KABOOM!
KABOOM!
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Estimates for efficiency , yield in X, Y, Z
Assume:
1. Type-II SNe enrich the ISM. (Neglect: Type-I SNe, stellar winds, PNe, ....)
2. Closed Box Model: (Neglect: Infall from the IGM, outflow to the IGM)
3. SN 1987A is typical Type-II SN.
Better models include these effects.
What do we know about SN 1987A?
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SN 1987A23 Feb 1987 in LMC
Brightest SN since 1604!
First SN detected in neutrinos.
Visible (14 --> 4.2 mag) to naked eye, in southern sky.
Progenitor star visible: ~20 Msun blue supergiant.
3- ring structure (pre-SN wind)
UV flash reached inner ring in 80 d. Fastest ejecta reached inner ring in ~6 yr. Fast ejection velocity v~c/30~11,000 km/s. Slower (metal-enriched) ejecta asymmetric.
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SN 1987A23 Feb 1987 in LMC
Brightest SN since 1604!
First SN detected in neutrinos.
Visible (14 --> 4.2 mag) to naked eye, in southern sky.
Progenitor star visible:~20 Msun blue supergiant.
3- ring structure (pre-SN wind)
Shockwave reaches inner ring 2003.
20032010
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Use SN 1987A to calculate and yield.
SN 1987A: progenitor star mass = 20 M remnant neutron star mass = 1.6 Mmass returned to the ISM = 18.4 M
From IMF, 7.2% of MS is in stars with M > 8 M
= Fraction of MS returned to ISM:
Star Formation Efficiency = fraction of MS retained in stars:
Star Formation Efficiency
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SN 1987A Lightcurve
56Ni => 56 Co 6d half-life 56Co => 56 Fe 78d half-life
Powered by radioactive decay of r-process nuclei. Use to measure metal abundances in ejected gas.
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X, Y, Z of ejecta from SN1987A
Initial mass ~ 20 M
NS mass ~ 1.6 M
Mass ejected ~ 18.4 M
in H 9.0 M
He 7.0 M = 18.4 M
Z 2.4 M
}
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Q1: What changes to the particle content of the expanding Universe occur at the epochs of:
• Annihilation: – pair soup -> quark soup (109 photons/quark)
• Baryogenesis:– quarks bound (by strong force) into baryons.– UUD = proton DDU = neutron
• Nucleosynthesis:– Atomic nuclei: 75% H, 25% He, traces of Li, Be
• Recombination: – Neutral atoms form as free electrons recombine– photons fly free
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Q2: Given present-day density parameters M = 0.3 for matter and R = 5x10-5 for radiation, at what redshift z were the energy densities equal ?
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Q3 a) Evaluate the neutron/proton ratio in thermodynamic equilibrium at high and low T.
b) Evaluate the n/p ratio and Yp if mn = mp.
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Q4 Alien’s CMB-meter reads 5.1K and 4.9K in the fore and aft directions. Evaluate the velocity.
Are humans present on Earth at this time?
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Assume a Universe filled with uniform density fluid. [ OK on large scales > 100 Mpc ]
Density: Energy density:
Critical density: 3 components: 1. Radiation 2. Matter “Dark Matter” baryons 3. “Dark Energy”
Total
Cosmological Models
Only ~4% is matter as we know it!
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Cold Matter: ( m > 0, p << mc )
Radiation: ( m = 0 ) Hot Matter: ( m > 0, p >> mc )
Energy Density of expanding box
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3 Eras: radiation…matter…vacuum
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• Q1: Given the density parameters =0.3 for matter and =0.7 for Dark Energy, evaluate the redshift z at which the energy densities of matter and Dark Energy are equal.
= crit ~ R-3 1 + z = R0 / R= crit ~ R0
whenz
• 1+z = ( / )1/3 = ( / )1/3 = 1.326• z = 0.326
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• Q2: What changes to the particle content of the expanding Universe occur at the following epochs:
• Annihilation: particles and anti-particles annihilate, producing photons. Small excess of particles (~1 per 109 photons)
• Baryogenesis: free quarks confined by strong force in (colourless) groups of 3 producing neutrons (ddu) and protons (uud).
• Nucleosynthesis: protons and neutrons bind to form 2D, then 4He. Yp set by p/n ratio, as virtually all n go into 4He leaving residual p as H.
• Recombination: H and He nuclei capture free electrons. Universe now transparent to photons.
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• Q3: If the neutron decay time were 1 s, rather than 900s, what primordial helium abundance Yp would emerge from Big Bang Nucleosynthesis?
• n(t) = n(0) exp(- t / )• p(t) = p(0)+(n(0)-n(t))• t~300s = 900s => 1s• Yp = 2n/(p+n) => 0 since virtually all
neutrons decay.
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• Q4: Name and describe three effects that give rise to anisotropy in the Cosmic Microwave Background, indicating which are most important on angular scales of 10, 1 and 0.1 degrees.
• 10o Sachs-Wolf effect - photons last scattered from higher-density regions lose energy climbing out of the potential well.
• 1o Doppler effect - velocity of gas on last-scattering surface shifts photon wavelengths.
• 0.1o Sunyaev-Zeldovich effect - re-ionised gas (e.g. X-ray gas in galaxy clusters) scatters CMB photons passing thru, changing photon direction and energy.
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= fraction of M0 in gas
= fraction of M0 that has beenturned into stars
In dimensionless form
slope = -
OK, since some gas is recycled.