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BB 1,2 H 3,4 He 7 Li Intergalactic medium Interstellar medium Galaxy formation inflowGal. winds, stripping, mergers Cosmic rays Small stars D, Li Middling.

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Presentation on theme: "BB 1,2 H 3,4 He 7 Li Intergalactic medium Interstellar medium Galaxy formation inflowGal. winds, stripping, mergers Cosmic rays Small stars D, Li Middling."— Presentation transcript:

1 BB 1,2 H 3,4 He 7 Li Intergalactic medium Interstellar medium Galaxy formation inflowGal. winds, stripping, mergers Cosmic rays Small stars D, Li Middling stars Big stars Star formation Spallation 6 Li, Be, B WD NS BH SN Explosive r-process Winds, PN, Novae He, 7 Li, C, N D, Li, Be, B ? Nucleosynthesis Flowchart

2 Lecture 9: Supernova Rates Star-Formation Efficiency, Yield How many supernovae per year for each galaxy type ? Use power-law IMF, Salpeter slope -7/3 = Limits of validity, not well known 20 M  0.1 M  8 M  slope = -7/3 = Supernova limit

3 “Universal” IMF (Kroupa 2002) log( M / M  )  MW MC GC local log( M / M  ) M42 M35 Pleiades local  ~ - 7/3 M > 1 M  - 4/ M  - 1/3 M < 0.1 M 

4 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

5 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

6 Median mass: Mean mass:. “Typical” SN Mass.

7 Spiral Galaxy: SFR: ~ 8 M  yr % have M > 8 M . (8 M  yr -1 ) x ~ 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

8 SN Rates: Ellipticals t * = 1 Gyr e-folding time t = 10 Gyr age  = 0.95 efficiency M 0 = M  total mass = initial gas mass Gas consumption: Star formation: SN rate: 3 SN per 10 5 yr. Negligible!.... gas stars

9 What Star Formation Efficiency  and Yields of H, He and Metals ? X = 0.75 Y = 0.25 Z = 0.00 X = ? Y = ? Z = ? M G = M 0 M S = 0 M G = 0 M S = M 0 M G = (1-  ) M 0 M S =  M 0  = ? KABOOM!

10 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?

11 SN 1987A 23 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.

12 SN 1987A 23 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

13 Use SN 1987A to calculate  and yield. SN 1987A: progenitor star mass = 20 M  remnant neutron star mass = 1.6 M  mass returned to the ISM = 18.4 M  From IMF, 7.2% of M S is in stars with M > 8 M   = Fraction of M S returned to ISM: Star Formation Efficiency  = fraction of M S retained in stars: Star Formation Efficiency

14 SN 1987A Lightcurve 56 Ni => 56 Co 6d half-life 56 Co => 56 Fe 78d half-life Powered by radioactive decay of r-process nuclei. Use to measure metal abundances in ejected gas.

15 X, Y, Z of ejecta from SN1987A Initial mass~ 20 M  NS mass~ 1.6 M  Mass ejected~ 18.4 M  in H9.0 M  He7.0 M  = 18.4 M  Z2.4 M  }

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17 Q1: What changes to the particle content of the expanding Universe occur at the epochs of: Annihilation: – pair soup -> quark soup (10 9 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

18 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 ?

19 Q3 a) Evaluate the neutron/proton ratio in thermodynamic equilibrium at high and low T. b) Evaluate the n/p ratio and Y p if m n = m p.

20 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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22 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!

23 Cold Matter: ( m > 0, p << mc ) Radiation: ( m = 0 ) Hot Matter: ( m > 0, p >> mc ) Energy Density of expanding box

24 3 Eras: radiation…matter…vacuum

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26 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 z = R 0 / R   =    crit ~ R 0     when     z       1+z = (   /   ) 1/3 = (  /  ) 1/3 = z = 0.326

27 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 10 9 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 2 D, then 4 He. Y p set by p/n ratio, as virtually all n go into 4 He leaving residual p as H. Recombination: H and He nuclei capture free electrons. Universe now transparent to photons.

28 Q3: If the neutron decay time were 1 s, rather than 900s, what primordial helium abundance Y p would emerge from Big Bang Nucleosynthesis? n(t) = n(0) exp(- t /  ) p(t) = p(0)+(n(0)-n(t)) t~300s  = 900s => 1s Y p = 2n/(p+n) => 0 since virtually all neutrons decay.

29 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. 10 o Sachs-Wolf effect - photons last scattered from higher-density regions lose energy climbing out of the potential well. 1 o Doppler effect - velocity of gas on last-scattering surface shifts photon wavelengths. 0.1 o 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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31 = fraction of M 0 in gas = fraction of M 0 that has been turned into stars In dimensionless form slope = -  OK, since some gas is recycled.


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