Evolution, Death and Nucleosynthesisof the First Stars
Alexander HegerStan Woosley
Ken ChenPamela Vo
Bernhad MüllerThomas Janka
Candace Joggerst
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First Stars IV, Kyoto, Japan, May 24, 2012
Motivation:
A Brief History of the Universe
`
Cosmic Dark Age
(after recombination)
time
What WeFind Today
What theBig Bang
made…
(The primordial abundance pattern)Brian Fields (2002, priv. com.)
(The solar abundance pattern)Lodders (2003)
(Pop III star yields)Heger & Woosley (2010)
Frebel et al. (2005)
© Alexander Heger Hubble Deep Field
Setting the Stage:
Pre-SupernovaEvolution and
Nucleosynthesis(Recap)
Once formed, the evolution of a star is governed by gravity: continuing contraction
to higher central densities and temperatures
Evolution of central density and temperature of 15 MꙨ
and 25 MꙨ stars
Nuclear Burning Stages
net nuclear energy generation (burning + neutrino losses)
net nuclear energy loss (burning + neutrino losses)
convection semiconvectiontotal mass of star(reduces by mass loss)ra
dia
tiv
e e
nv
elo
pe
(blu
e g
ian
t)
convective envelope (red super giant)
H b
urn
ing
He
bu
rnin
g
C b
urn
ing
(rad
iati
ve)
C s
hel
lb
urn
ing
Ne O
burning
C shell burning
OO O O shell burning
Si
Si
Fuel MainProduct
SecondaryProduct
T(109 K)
Time(s)
Main Reaction
Innermostejecta
r-processνp-process
- >10? 1 (n,γ), β−
Si, O 56Ni iron group >4 0.1 (α,γ)
O Si, S Cl, Ar,K, Ca 3 - 4 1 16O + 16O
O, Ne O, Mg, Ne Na, Al, P 2 - 3 5 (γ,α)
p-process11B, 19F,
138La,180Ta2 - 3 5 (γ ,n)
ν-process 5 (ν, ν’), (ν, e-)
Explosive Nucleosynthesisin supernovae from massive stars
Eje
cted
“m
etal
s”
Naoki Yoshida:
● stars● massive stars● very massive stars● very very massive stars● very very very massive stars● very very very very massive stars● very very very very very massive stars● very very very very very very massive stars● very very very very very very very massive stars● very very very very very very very very massive stars
“Beers Scale”
adopted from Beers and Christlieb
+ stars that do not enter hydrostatic burning
Open Questions
?
?
Eta Car – a really big star in our galaxy today
Nathan Smith, 2007, First Stars III
Mass Loss due to Giant Eruptions?
How do the most massive stars evolve?
● Reduced mass loss on the main sequence followed by LBV & giant eruptions?
● What are these eruptions? (physics, number, recurrence)
● When do they occur? (internal evolution stage?)
● How do we model these eruptions?● Pulsational Pair-Instability Supernovae (PPSN)?
Initial Rotation of Massive Stars
Pop I/II
Pop III
Initial Rotation of Massive Stars
Pop I/II
Pop III
star disk
Mass Loss due to Critical Rotation
ANGULAR MOMENTUM
mass
● How important is mass loss due to critical (or fast) rotation? ● How do we quantify mass loss and angular momentum loss?● How does it effect our stellar models?
(Langer, Meynet, Maeder, Hirschi,...)
(Yoon et al. 2012)
Nucleosynthesis in Low-Mass
Core CollapseSupernovae
Low-Mass Pre-SN Structure
z9.6
u8.1
Mueller, Janka, Heger (2012, in prep.)
Explosion of Low-Mass SN
2D simulation with neutrino transport and core cooling
Explosion driven by convection not SASI
Explosion starts fast as accretion drops very rapidly
n-Rich Ejecta Low-Mass SN
-> May produce elements below 1st r-process peak
Mueller, Janka, Heger (2012, in prep.)
z9.6A
R-Process in Low-Mass SN
r-precess initiated for explosion with a few times 0.1 B
z9.6a
R-Process in Low-Mass SNr-precess initiated for explosion with a few times 0.1 B
z9.6b
R-Process in Low-Mass SN
r-precess initiated for explosion with a few times 0.1 B
z9.6B
R-Process in Low-Mass SN
r-precess initiated for explosion with a few times 0.1 B
Impact of rotation on s-process element production in very-metal-poor massive stars.
C Chiappini et al. Nature 472, 454-457 (2011)
doi:10.1038/nature10000
Supernova Progenitor Masses
(Smartt 2009)
Presupernova stars for Type IIp and II-L
Solid Line: Salpeter IMF with 16.5 M
Θ cutoff
Dotted Line: Salpeter IMF with 35 M
Θ cutoff
► Exclude stars with M
initial > 20 M
Θ as
Type IIP/IIL progenitors at 95% confidence level?
Nucleosynthesis in
Massive Pop III Stars
Supernovae, Nucleosynthesis, & Mixing
SN + mixing SN, no mixing
Pop III NucleosynthesisElemental Yieldsas a function of initial mass
non-rotating stars
120 stellar masses
“complete” reaction network
normalized to Mg
RESULTS:e.g.,Production of 7Li by neutrino interaction in very compact stellar envelope!
Mg yield (ejecta mass fraction)
20 30 40 50
Heger & Woosley (2010)
What Can Nucleosynthesis
Do for Us?
➞
Reconstruction of the IMF
primordial stars form,nucleosynthesis ejected
ejecta incorporated in low-Z halo stars
find low-Z halo stars(HERES, SEGUE, …)
measure abundances(VLT, KECK, …)
compare abundances to primordial star
nucleosynthesis library
obtain IMF of population of progenitor stars
Frebel, priv. com. (2007)
Umeda & Nomoto, Nature, 422, 871, (2003)
25 solar mass star, Pop III0.3 B, mildly mixed8x10-6 solar masses iron
Comparison to Observational DataThe most iron-poor star
Heger & Woosley (2010)
different explosion energies
The second most iron-poor star
~1/1000 solar metallicity stars
Fit to Caffau Star10.6 MꙨ
0.9 B
Vo et al. (2012 in prep)
Reconstruction of the IMF
Vo et al. (2012 in prep)
Pair-InstabilitySupernovae
PISNPCSN hypernovaepair production SNe
}PSN
pulsational pair-instability SNe ➞ PPSN
A Good Name?
Nucleosynthesis in
Pair-InstabilitySupernovae
Initial mass: 150MꙨ
Initial mass: 250MꙨ
Initial mass: 150MꙨ
Initial mass: 250MꙨ
expl
osio
n en
ergy
/ B
approximate
E expl
Fe-richFe-poor
•Low neutron excess from CNO -> 22Ne in helium burning
•No extended stable period of carbon and oxygen burning where weak interactions might increase the neutron excess
ProblemPair-Instability Supernovae do
not reproduce the abundances as observed in very metal poor halo stars!
The IMF or the First Stars – and hence how they come to pass – still remains elusive without observational data
Summary● Uncertainties in Fates of the First Stars largely come from
uncertainties in their initial properties: mass, rotation, binarity
● Significant uncertainty also exists in the modeling of the stellar physics of primordial stars – very massive stars in general, but particularly, as with all theory, if there is no experimental (observational) constrain
● Stellar forensics, determining abundance patterns of what the first stars left behind, may be our best tool in the near future (e.g., constraints on pair-SNe)
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