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Supernova Cosmology Bruno Leibundgut European Southern Observatory

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Supernovae Walter Baade ( ) Fritz Zwicky ( ) SN 1937C: Baade and Minkowski

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SN 1994D

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Supernova 11. March 13. March 16. March 29. March 5. April SN 1997as z=0.51 Supernova light curve

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© R. Fosbury/ESA/NASA/ESO Supernova Remnant (SN 1054)

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Suntzeff Observing supernovae SINS

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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)

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Supernova models

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1 Si O C He H Onion-like structure of a massive presupernova star several million years after its birth: mass: M sun radius: R sun - 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

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Thermonuclear Supernovae White dwarf in a binary system Growing to the Chandrasekhar mass (M Chand =1.4 M ) by mass transfer from a nearby star The “standard model” © ESA

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White dwarfs as Ia progenitors White Dwarfs are the most likely progenitor stars for Type Ia Supernovae Nuclear burning phase finished Gravity provides the energy for emission Degenerate electron gas Extremely compact stars Sun will be the size of the earth as a white dwarf Gamow (1970)

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The "standard model" He (+H) from binary companion Explosion energy: Fusion of C+C, C+O, O+O "Fe“ Density ~ g/cm Temperature: a few 10 9 K Radii: a few 1000 km C+O, M ≈ M ch

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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

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Energy sources gravity →Type II supernovae collapse of a solar mass or more to a neutron star release of erg − mostly ν e − erg in kinetic energy (expansion of the ejecta) − erg in radiation nuclear (binding) energy → Type Ia explosive C and O burning of about one solar mass release of erg

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Isotopes of Ni and other elements conversion of - rays and positrons into heat and optical photons Diehl and Timmes (1998) Radioactivity Contardo (2001)

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The expansion of the universe Luminosity distance in an isotropic, homogeneous universe as a Taylor expansion Hubble’s Lawaccelerationjerk/equation of state

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The nearby SN Ia sample and Hubble’s law Evidence for good distances

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Determining H 0 from explosion models Hubble’s law Luminosity distance Ni-Co decay

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H 0 from the nickel mass Hubble law Luminosity distance Arnett’s ruleNi-Co decay and 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=αE Ni ) ε(t): energy deposited in the supernova ejecta

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Comparison with models MPA W7 Different Ni masses for SNe Ia have been inferred no unique mass applicable only lower limit for H 0 can be derived Stritzinger & Leibundgut 2005

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Comparison with models Stritzinger & Leibundgut 2005

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

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Friedmann cosmology Assumption: homogeneous and isotropic universe Null geodesic in a Friedmann-Robertson-Walker metric:

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Riess et al Measure acceleration acceleration

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Cosmological implication ΩΛΩΛ ΩMΩM No Big Bang Empty Universum Einstein – de Sitter Lambda-dominated Universe Concordance Cosmology

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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 ) = 8 G [ T (matter) + T (new) ] ????

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General luminosity distance with and M = 0 (matter) R = ⅓ (radiation) = -1 (cosmological constant) The equation of state parameter

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

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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 unstable Pair of scalars: “crossing” from w>-1 to w<-1 Physical issues w = -1 w < -1

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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 ω to 10% overall

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SNLS – The SuperNova Legacy Survey World-wide collaboration to find and characterise SNe Ia with 0.2 < z < 0.8 Search with CFHT 4m telescope Spectroscopy with VLT, Gemini, Keck, Magellan Goal: Measure distances to 1000 SNe Ia with an overall accuracy of 5% determine ω to 7% overall

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ESSENCE spectroscopy Matheson et al. 2005

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First two years of ESSENCE spectra Matheson et al. 2005

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SNLS 1 st year results Astier et al. For a flat CDM cosmology : Combined with BAO (Eisenstein, 2005) : Ω M =0.264±0.042 (stat) ± (sys) Ω M = 0.271± (stat) ± (sys) w = ± 0.09 (stat) ± (sys) Based on 71 distant SNe Ia:

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

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Line velocities Blondin et al. 2005

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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

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

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Time-dependent w(z) Maor, Brustein & Steinhardt 2001 Luminosity Distance vs redshift can be degenerate for time- varying ω(z)

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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.

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Nature of the Dark Energy? Currently four proposals: cosmological constant

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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

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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

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Summary H 0 > 40 km s -1 Mpc -1 (3σ), if the thermonuclear model of Type Ia supernovae is correct Explosion models still under-predict the 56 Ni 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

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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

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