Supernova cosmology. The quest to measure the equation of state of dark energy. Bruno Leibundgut European Southern Observatory

Transcription

1 Supernova cosmology The quest to measure the equation of state of dark energy Bruno Leibundgut European Southern Observatory

2 Outline Cosmological background Supernovae One-stop shopping for the Hubble constant Acceleration and Dark energy The equation of state parameter of dark energy

3 The expansion of the universe Luminosity distance in an isotropic, homogeneous universe as a Taylor expansion + ± + + = ) ( ) ( O z z R H c j q q z q H cz D L a a H & = = H a a q & & = H a a j &&& Hubble s Law acceleration jerk/equation of state

4 Connecting expansion to physics Hubble law: D = cz H 0 Acceleration: cz 1 D = 1 + (1 q ) z 0 H 2 0 Equation of state: D = O( z 3 )

5 Supernova light curve

6 Supernova classification Based on spectroscopy core collapse in massive stars SN II (H) SN Ib/c (no H/He) Hypernovae/GRBs SN Ia (no H) thermonuclear explosions

7 Classification

8 Observing supernovae SINS Suntzeff

9 Observing supernovae Suntzeff 28 Virgo distance 33

10 Observing supernovae Suntzeff gap z=

11 SN 1994D

12 The nearby SNe Ia excellent coverage for a few objects fairly complete picture allows detailed comparisons with models Krisciunas et al. (2003) SN 2003du European Supernova Collaboration

13 Pignata et al. (2004) Comparison with models

14 The nearby SN Ia sample and Hubble s law Evidence for good distances Germany et al. 2004

15 Determining H 0 from models Hubble s law Luminosity distance Ni-Co decay v D = = H D L = cz 0 H 0 L 4πF E Ni = λ λ Ni Ni λ λ Co Co Q Ni λ λ Ni Co λnit λcot 1 QCo e + QCoe N Ni,0

16 H 0 from the nickel mass H 0 = cz D = cz 4πF L = cz 4πF 4πF = cz αe αε ( t) M Ni Ni Hubble Luminosity law distance Arnett s rule Ni-Co decay and rise time a: conversion of nickel energy into radiation (L=aE Ni ) e(t): energy deposited in the supernova ejecta Need bolometric flux at maximum F and the redshift z as observables Stritzinger & Leibundgut (2005)

17 Assumptions Rise time (15-25 days) about 10% uncertainty Arnett s rule energy input at maximum equals radiated energy (i.e. a 1, e(t max ) 1) Nickel mass from models uniquely defines the bolometric peak luminosity

18 Comparison with models MPA W7 1M

19 Acceleration Originally thought of as deceleration due to the action of gravity in a matter dominated universe cz 1 D = 1 + (1 q ) z 0 H 2 0 q 0 a&& = H a 2 0

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21 Friedmann cosmology Assumption: homogeneous and isotropic universe Null geodesic in a Friedmann-Robertson-Walker metric: D L = (1 + H 0 z) c Ω κ S Ω κ z 0 [ Ω + z + Ω + z + Ω ] 2 3 (1 ) (1 ) κ M Λ 1 2 dz 8πG ρ Ω 2 2 M = 2 M Ωk = Ω 2 3H 2 Λ = 2 0 R H0 3H0 kc Λc

22 Measure acceleration relative distance distance (Mpc) acceleration redshift

23 Cosmological implication O? No Big Bang Empty Universum Einstein de Sitter Lambda-dominated Universe Concordance Cosmology O M

24 Riess et al Evidence for the O?

25 Adding jerk Riess et al. 2004

26 Measure deceleration acceleration Tonry et Riess al et al. 2004

27 What is Dark Energy? G µν + f(g µν ) = 8πG [ T µν (matter) + T µν (new) ]???? Two philosophically distinct possibilities:? Gravitational effect, e.g. Cosmological Constant, or gravity leaking into extra dimensions? A Vacuum energy effect, decaying scalar field New Fundamental Physics!

28 The equation of state parameter w D L General luminosity distance = 1 z 2 ( 1 + z) c Ω 2 Ω + + 3(1+ ωi ) S z Ω + z dz κ κ (1 ) i(1 ) H0 Ωκ 0 i with Ω = 1 Ω and ω = i κ i i 2 i ρic w M = 0 (matter) w R =? (radiation) w L = -1 (cosmological constant) p

29 Dark Energy Equation of State Current Limit on Dark Energy: w < dF prior Spergel et. al Tonry et. al. 2003

30 Dark Energy Models w > -1 w = -1 w < -1 Quintessence Gravitational, e.g. R -n with n>0 (Carroll et. al. 2004) Cosmological Constant Exotic! (Carroll et. al. 2003) In general unstable Pair of scalars: crossing from w>-1 to w<-1 Physical issues

31 ESSENCE World-wide collaboration to find and characterise SNe Ia with 0.2<z<0.8 Search with CTIO 4m Blanco telescope Spectroscopy with VLT, Gemini, Keck, Magellan Goal: Measure distances to 200 SNe Ia with an overall accuracy of 5% determine? to 10% overall

32 ESSENCE spectroscopy Matheson et al. 2005

33 ESSENCE spectroscopy (cont.)

34 First two years of ESSENCE spectra Matheson et al. 2005

35 Spectroscopic study Blondin et al. 2005

36 w < 0.73(95%) Tonry et al. 2003

37 SN Ia and 2dF constraints Use constraints from 2dF and 2dF: WMAP W M h = 0.2 ± 0.03 KP: h = 0.72 ± 0.08 Cosmic strings Quintessence Cosmological constant Tonry et al Knop et al. 2003

38 And on to a variable? Ansatz:? (z)=? 0 +? z Riess et al. 2004

39 Time-dependent w(z) Luminosity Distance vs redshift can be degenerate for timevarying? (z) Maor, Brustein & Steinhardt 2001

40 SN Projects SN Factory Carnegie SN Project ESSENCE CFHT Legacy Survey Higher-z SN Search (GOODS) SNAP

41 Four redshift regimes z<0.05 Define the characteristics of Type Ia supernovae Understand the explosion and radiation physics Determination of H 0 z<0.3 Explore the systematics of SNe Ia Establish distance indicator

42 Four redshift regimes (cont.) 0.2<z<0.8 Measure the strength of the cosmic acceleration (dark energy) z>0.8 break the degeneracy measure matter density All redshifts Measure details of dark energy

43 The SN Ia Hubble diagram powerful tool to measure the absolute scale of the universe H 0 measure the expansion history (q 0 ) determine the amount of dark energy measure the equation of state parameter of dark energy

44 Caveats Warning to the theorists: Claims for a measurement of a change of the equation of state parameter? are exaggerated. Current data accuracy is inadequate for too many free parameters in the analysis.

45 Summary Type Ia supernovae appear currently the most promising route to provide a possible answer to what the Dark Energy is. All redshifts need to be covered distant SNe Ia alone are useless nearby SNe Ia are the source of our understanding of the distance indicator