Supernova Cosmology

Bruno LeibundgutEuropean Southern

Observatory

Supernovae

Walter Baade (1893-1960) Fritz Zwicky (1898-1974)

SN 1937C: Baade and Minkowski

SN 1994D

Supernova

11. March

13. March

16. March

29. March

5. AprilSN 1997asz=0.51

Supernova light curve

SN 1987ASN 1987A

© R. Fosbury/ESA/NASA/ESO

Supernova Remnant (SN 1054)

Suntzeff

Observing

supernovae

SINS

Supernova classification

Based on spectroscopy

core collapse in massive stars

SN II (H)SN Ib/c (no H/He)Hypernovae/GRBs thermonuclear

explosions

SN Ia (no H)

Supernova models

Si

OC

He

H

Onion-like structureof a massive presupernova star several millionyears after its birth:

mass: 10 ... 102 Msun

radius: 50 ... 103 Rsun

- shells of different composition are separated by active thermonuclear burning shells - core Si-burning leads to formation of central iron core

Note: figure not drawn to scale!

Core-collapse supernovae

Thermonuclear Supernovae

White dwarf in a binary system

Growing to the Chandrasekhar mass (MChand=1.4 M) by mass transfer from a nearby star

The “standard model”

© ESA

White dwarfs as Ia progenitors

White Dwarfs are the most likely progenitor stars for Type Ia SupernovaeNuclear burning phase finishedGravity provides the energy for emissionDegenerate electron gas

Extremely compact starsSun will be the size of the earth as a

white dwarf

Gamow (1970)

The "standard model"

He (+H)from binarycompanion

Explosion energy:

Fusion ofC+C, C+O, O+O "Fe“Density ~ 109 - 1010 g/cm

Temperature: a few 109 K

Radii: a few 1000 km

C+O,C+O,

M ≈ MM ≈ Mchch

Supernova types

thermonuclear SNe• from low-mass

stars (<8M)• highly evolved

stars (white dwarfs)

• explosive C and O burning

• binary systems required

• complete disruption

core-collapse SNe• high mass stars

(>8M)• large envelopes

(still burning)• burning due to

compression• single stars

(binaries for SNe Ib/c)

• neutron star

Energy sources

gravity →Type II supernovae• collapse of a solar mass or more

to a neutron star release of 1053 erg

− mostly νe

− 1051 erg in kinetic energy (expansion of the ejecta)− 1049 erg in radiation

nuclear (binding) energy → Type Ia• explosive C and O burning of about

one solar massrelease of 1049 erg

Isotopes of Ni and other elements• conversion

of -rays and positrons into heat and optical photons

Diehl and Timmes (1998)

Radioactivity

Contardo (2001)

The expansion of the universe

Luminosity distance in an isotropic, homogeneous universe as a Taylor expansion

)(31

6

1)1(

2

11 32

220

2

02000

0

zOzRH

cjqqzq

H

czDL

a

aH

0

200 H

a

aq

300 H

a

aj

Hubble’s Law acceleration jerk/equation of state

The nearby SN Ia sample and Hubble’s

law

Evidence for gooddistances

Determining H0 from explosion models

Hubble’s law

Luminosity distance

Ni-Co decay

00 H

cz

H

vD

F

LDL 4

0,1 Nit

Cot

CoCo

NiNi

CoNi

CoNiNi NeQeQQE CoNi

H0 from the nickel mass

NiNi Mt

Fcz

E

Fcz

L

Fcz

D

czH

)(

4440

Hubble lawLuminosity distance

Arnett’s rule Ni-Co decayand rise time

Need bolometric flux at maximum F and the redshift z as observables Stritzinger & Leibundgut 2005

α: conversion of nickel energy into radiation (L=αENi)ε(t): energy deposited in the supernova ejecta

Comparison with models

MPA

W7

Different Ni masses for SNe Ia have been inferred

•no unique mass applicable

•only lower limit for H0 can be derived

Stritzinger & Leibundgut 2005

Comparison with models

Stritzinger & Leibundgut 2005

Acceleration

Originally thought of as deceleration due to the action of gravity in a matter dominated universe

zq

H

czD )1(

2

11 0

0

200 H

a

aq

Friedmann cosmologyAssumption:homogeneous and isotropic universe

Null geodesic in a Friedmann-Robertson-Walker metric:

zdzzSH

czD

z

ML

21

0

32

0

)1()1()1(

MM H

G 203

8

20

2

2

HR

kck

20

2

3H

c

Riess et al. 2004

Measure acceleration

acceleration

Cosmological implication

ΩΛ

ΩM

No

Big

Ban

g

Empty UniversumEinstein – de SitterLambda-dominated

UniverseConcordance

Cosmology

What is Dark Energy?

New Fundamental Physics!

Two philosophically distinct possibilities:

● Gravitational effect, e.g. Cosmological Constant, or gravity “leaking” into extra dimensions

● A “Vacuum energy” effect, decaying scalar field

G + f(g) = 8G [ T(matter) + T(new) ]

????

General luminosity distance

• with and

M= 0 (matter)

R= ⅓ (radiation)

= -1 (cosmological constant)

zdzzS

H

czD

z

iiL

i

21

0

)1(32

0

)1()1()1(

i

i1 2c

p

i

ii

The equation of state parameter

Dark Energy Equation of State

Current Limit on Dark Energy: w < -0.7

2dF prior

Tonry et. al. 2003

Spergel et. al. 20032003

Dark Energy Descriptions

w > -1 Quintessence

Gravitational, e.g. R-n with n>0 (Carroll et. al. 2004)

Cosmological Constant

Exotic! (Carroll et. al. 2003)In general unstablePair of scalars: “crossing” from

w>-1 to w<-1Physical issues

w = -1

w < -1

ESSENCEWorld-wide collaboration to find and characterise SNe Ia with 0.2 < z < 0.8Search with CTIO 4m Blanco telescopeSpectroscopy with VLT, Gemini, Keck, MagellanGoal: Measure distances to 200 SNe Ia with an overall accuracy of 5% determine ω to 10% overall

SNLS – The SuperNova Legacy Survey

World-wide collaboration to find and characterise SNe Ia with 0.2 < z < 0.8Search with CFHT 4m telescopeSpectroscopy with VLT, Gemini, Keck, MagellanGoal: Measure distances to 1000 SNe Ia with an overall accuracy of 5% determine ω to 7% overall

ESSENCE spectroscopy

Matheson et al. 2005

First two years of ESSENCE spectra

Matheson et al. 2005

SNLS 1st year results

Astier et al.

For a flat CDM cosmology :

Combined with BAO (Eisenstein, 2005) :

ΩM=0.264±0.042 (stat) ± 0.032 (sys)

ΩM = 0.271± 0.021 (stat) ± 0.007 (sys) w = -1.02 ± 0.09 (stat) ± 0.054 (sys)

Based on 71 distant SNe Ia:

Spectroscopic study

Blondin et al. 2005

Comparing the line velocity evolution of nearby and distant SNe Ia should allow us to check for systematic differences, i.e. evolution

Line velocitiesBlondin et al. 2005

Line velocities

No significant differences in the line velocity evolution observed• implies similar density structure and

element distribution• explosion and burning physics similar

Peculiarities observed in nearby SNe Ia also observed in the some distant objects• detached lines

The properties of distant SNe Ia are indistinguishable from the nearby ones with current observations

And on to a variable ω

Ansatz:

ω(z)= ω 0+ ω’z

Riess et al. 2004

Time-dependent w(z)

Maor, Brustein & Steinhardt 2001

Luminosity Distance vs redshift can be degenerate for time-varying ω(z)

Caveat

Warning to the theorists:

Claims for a measurement of a change of the equation of state parameter ω are exaggerated. Current data accuracy is inadequate for too many free parameters in the analysis.

Nature of the Dark Energy?

Currently four proposals:• cosmological constant

Nature of the Dark Energy?

Currently four proposals:• cosmological constant• quintessence

– decaying particle field– signature:

– equation of state parameter with

• leaking of gravity into a higher dimension

• phantom energy leads to the Big Rip

2c

p

1

The SN Ia Hubble diagram

• powerful tool to• measure the absolute scale of the

universeH0

• measure the expansion history (q0)

• determine the amount of dark energy

• measure the equation of state parameter of dark energy

Summary

H0 > 40 km s-1 Mpc-1 (3σ), if the thermonuclear model of Type Ia supernovae is correct• Explosion models still under-predict the 56Ni

mass

Nearby SNe Ia are the source of our understanding of the distance indicator

No evolutionary effects observed so far for the distant SNe Ia

All redshifts need to be covered• distant SNe Ia alone are useless

Summary

The determination of the (integrated) ω will become available in about two years • CFHT Supernova Legacy Survey (SNLS)

– Goal: 700 SNe Ia ⇒ Δω=7%– First result (one year of data) indicate ω=-1 to within

almost 10%Finished in 2007

• ESSENCE– Goal: 200 SNe Ia ⇒ Δω=10%– Lot of work to investigate the systematics

(spectroscopy)Finished in 2006