SN 1994D in NGC 4526 Supernovae Type Ia Brightest Objects in Normal Galaxies
9 MB ≈−19.5mag about 5 × 10 L⊙ Remarkable Standard Candles Baade 1938
∆MB ≈±0.5mag or ± 60% in L
Cosmology Projects A correlation between peak L and light curve shape
reduces MB to ±0.15mag or 15% in L Phillips A) SN 1998M z =0.63 B) SN 1998J z =0.83 C) SN 1997cj z =0.50 D) SN 1998I z =0.89 Type Ia Supernovae
Perlmutter, Physics Today (2003) 0.0001 26 Supernova Cosmology Project 24 High-Z Supernova Search 0.001 22 fainter Calan/Tololo 25 empty 0.01 Supernova Survey 0 20 mass 0.20.4 0.6 1.0 1 density 18 24 0.1 with vacuum energy Relative brightness 16 1 23 without vacuum energy 14 0.01 0.02 0.04 0.1
22 Accelerating Universe magnitude
21 Decelerating Universe
20 0.2 0.4 0.6 1.0 redshift
0.8 0.7 0.6 0.5 Scale of the Universe [relative to today's scale] Perlmutter et al. and Riess et al.
The Universe is accelerating – ΩΛ at z =1 SNe Ia are 30% fainter than if ΩΛ =0
(a factor of 2 fainter if ΩM =1, ΩΛ =0)
Nucleosynthesis SNe Ia are a major source of Fe – Fe is lost in neutron stars
Binary Star Evolution Progenitor evolution is convoluted Supernova Types Main Classification-spectral Type II – hydrogen lines (most common) Type I – no hydrogen lines Ib–noSilines Ic–noSiorHe Ia – prominent Si lines
Type II – deaths of massive stars M ≥ 8 M⊙
Degenerate processed core exceeds MCh – collapse to a neutron star
46 13 EB ≈ 3 × 10 J ≈ 10 L⊙ × 3 months – mostly in neutrinos – H-envelope is ejected
Type Ib/c – deaths of very massive stars M ≥ 40 M⊙ Core collapse after mass loss – Wolf–Rayet or binary stars Type Ia – thermonuclear explosions of CO white dwarfs Available nuclear energy can exceed the WD binding energy most reaches nuclear statistical equilibrium 56 and about 0.8 M⊙ of Ni is expelled 56Ni → 56Co → 56Fe observed 12 16 56 44 Energy – 1 M⊙ of 20% C + 80% O → Fe releases 1.8 × 10 J 56 56 43 Decay of 1 M⊙ of Ni → Fe releases 2 × 10 J of this 9 enough for 80days at 5 × 10 L⊙ White Dwarfs and the Cores of Giants Objects supported entirely by electron degeneracy pressure Heisenberg Uncertainty ∆x∆p ≥ ¯h/2 All available low-energy electron states occupied Reducing the volume squeezes electrons to higher momentum states Work must be done and a pressure is exerted
Maximum mass – Chandrasekhar – MCh =1.44 M⊙ Reached when electrons become relativistic
Nuclear ash accumulates in the cores of stars When all fuel is exhausted the core shrinks The star expands – erythrogigantism Energy per Nucleon Detonation by Mass Accretion
As MWD increases towards MCh collapse and heating can ignite fusion
CO WDs explode at about 1.38 M⊙ – Enuc >Ebind full processing to 56Ni
ONe WDs ignite too late – Ebind is not exceeded collapses to a NS – energy lost in neutrinos
He WDs ignite early when MWD ≈ 0.7M⊙ – Enuc ≫ Ebind degeneracy raised – no explosion? Mass Accretion requires a binary companion Central Ignition Ignition at the Outside Carbon Ignition Slow accretion Rapid accretion
Central cold fusion ignition Edge hot fusion ignition Type Ia supernova Burns to an ONe white dwarf How can the Companion get Close Enough?
The White Dwarf was the core of a Red Giant
Unstable Mass Transfer and Common Envelope Evolution Common Envelope Evolution