1. ASIAANTUPHYS CosPA Seminar May 28, 2001 1 Supernovae and Acceleration of the Universe A journal club K. Y. Lo

2. ASIAANTUPHYS CosPA Seminar May 28, 2001 2 Papers reviewed: 1. Supernova explosions in the Universe –Adam Burrows, 2000, Nature, 403, 727 2. Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant –Reiss et al, 1998, AJ, 116, 1009. 3. Measurements of  and  from 42 High Redshift Supernovae – Perlmutter et al, 1999, ApJ, 517, 565

3. ASIAANTUPHYS CosPA Seminar May 28, 2001 3 Geometry and Dynamics of the Universe Robertson-Walker metric: d  2 = dt 2 – a(t) 2 [dr 2 /(1 – r 2 /R 2 ) + r 2( d  2 + sin 2  d  2 )] –Scale factor, a(t) and radius of curvature, R History and Fate of the Universe: a(t) = ? ä/a = – 4  G(3p +  )/3 +  /3 = H o 2 [   –  m (1+z) 3 /2], (å/a) 2 = 8  G  /3 – 1/R 2 a 2 +  /3 = H o 2 [   +  m (1+z) 3 +  R (1+z) 2 ] Accelerating Universe: ä > 0  [   –  m (1+z) 3 /2] > 0 Taylor-expansion of a(t) at t o, the present: a(t) = a(t o )[1 + H o (t – t o ) – ½q o H o 2 (t - t o ) 2 + …] H o = å(t o )/a(t o ), q o = – ä (t o )/[H o 2 a(t o )], a(t o )/a(t) = 1 + z

4. ASIAANTUPHYS CosPA Seminar May 28, 2001 4 Hubble diagram of Standard Candles at various z: F = L/4  d L 2 = L/4  (a o r z ) 2 (1+z) 2 –F = Observed flux (erg/s/cm 2, or apparent magnitude) –L = Intrinsic luminosity (erg/s, or absolute magnitude) –d L = Luminosity distance = f(z,  ,  m ) = f’(z, q o, H o ) = H o -1 |  k | -½ sinn{|  k | ½  z [(1+z) 2 (1+  m z) – z(2+z)   ] -½ dz} = H o -1 z [1 + (q o – 1)z + …] -½, z < 1 –If  =   +  m only, q o =  m /2 –   Hubble Diagram: Apparent magnitude vs z plot m = M + 5 log[H o d L (z,  ,  m )] – 5 log H o + 25 Need Standard Candles at large z (~1) !! How to measure q o ?

5. ASIAANTUPHYS CosPA Seminar May 28, 2001 5 Standard Candles at large z Bright: to be detectable –~25 mag detection limit; absolute magnitude ~ -20 mag Intrinsic luminosity known First ranked galaxies in distant clusters (cf. Sandage 1988) –Evolution of galaxies –Scott effect/Mahmquist bias –Extinction, k-correction, aperture,... Type I SNe (SCP, HSS projects) – Searches for high z SNe –Calibrate Intrinsic luminosity with nearby sample: Luminosity - light-curve shape correlation: empirical standards

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7. ASIAANTUPHYS CosPA Seminar May 28, 2001 7 Supernovae (cf Viewgraphs) Type II (no H in spectra) –Core collapse: > 11 M(solar) stars, burn through to Fe, succumb to gravity, collapse to neutron star, blows off mantle Type I (H in spectra) –Thermonuclear Incineration: Binary system with a white dwarf; mass transfer pushes WD to above Chandrasekhar limit; C,N,O burns explosively –10  less frequent; 10  brighter at peak; 10  more Fe produced –Energy release ~ burning 1.4M(solar) of C to Fe ~ standard candle ? 1 SN every second in the Universe –Galaxy: 1 SN every 30 to 50 years; one Type Ia every 300 years –SN search: ~ 10 SNe per night

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12. ASIAANTUPHYS CosPA Seminar May 28, 2001 12 Perlmutter et al 1999 ApJ, 483, 565

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19. ASIAANTUPHYS CosPA Seminar May 28, 2001 19 Perlmutter et al 1999 ApJ, 483, 565 Supernova Cosmology Project (>1988): LBL, Berkeley, Cambridge, Spain, Australia, STScI, Fermi Lab 42 SNe: 0.18 < z < 0.83 + Calan/Tololo nearby SNe: z < 0.1 –L fixed by light-curve width-luminosity correlation Hubble diagram fit by various models of d L –Inconsistent with =0, flat cosmology –0.8  m – 0.6   = 0.2 ± 0.1 –If  =1,   ~ 0.7 ± 0.1,  m ~ 0.3 ± 0.1 – t o ~ 14.9 ± 1.3 (0.63/h) Gyr

20. ASIAANTUPHYS CosPA Seminar May 28, 2001 20 Reiss et al 1998 AJ, 116, 1009 High z SN Search: Berkeley, Harvard, Chile, STScI, U. Wash, Mt. Stromlo, Michigan –CTIO 4m CCD; spectroscopy with Keck, MMT –10 + 16 high-z SNe: 0.16 < z < 0.97 –34 nearby SNe Hubble diagram constrains H o, q o, t o,  ,  m –   > 0 and q o < 0 at 3  confidence level –If  = 1,   > 0 at 7  –  m ruled out at 7  level –t o = 14.9 ± 1.7 Gyr

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27. ASIAANTUPHYS CosPA Seminar May 28, 2001 27 Uncertainties & the Future Intrinsic luminosity/Evolution of SNe Type Ia K-correction: emitted wavelength red-shifted by (1+z) Extinction (intrinsic and Galactic) Selection bias (Scott-Mahmquist) Local Void (in-homogeneity) Gravitational lensing (affects apparent magnitude) Contamination by non-Type Ia SN  SNe at z > 1; SN light red-shifted to IR: NGST etc

28. ASIAANTUPHYS CosPA Seminar May 28, 2001 28 SN at z = 1.7 Reiss et al, April 2001 HST: 1997 - 1995 Brighter than expected for steady state expansion: deceleration !?

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31. ASIAANTUPHYS CosPA Seminar May 28, 2001 31 Conclusion More observations needed ! More observations will come ! Theorists can go on theorizing, but there will be a day of reckoning, which is what makes physics real and fun !