bb 1,2 h 3,4 he 7 li intergalactic medium interstellar medium galaxy formation inflowgal. winds,...
TRANSCRIPT
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
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
“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
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
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
Median mass:
Mean mass:
.
“Typical” SN Mass
.
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
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
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!
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?
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.
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
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
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.
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
}
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
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 ?
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.
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?
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!
Cold Matter: ( m > 0, p << mc )
Radiation: ( m = 0 ) Hot Matter: ( m > 0, p >> mc )
Energy Density of expanding box
3 Eras: radiation…matter…vacuum
• 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
• 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.
• 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.
• 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.
= fraction of M0 in gas
= fraction of M0 that has beenturned into stars
In dimensionless form
slope = -
OK, since some gas is recycled.