SN Conference, Yukawa Institute for Theoretical Physics, Kyoto, Japan, Oct. 29, 2013

Evolution ofMassive Stars
Alexander Heger (Monash)
Stan Woosley (UCSC)
Chris West (UMN)
Ken Chen (UCSC)
Tuguldur Sukhbold (UCSC)
Duligur Ibeling (Harvard)

http://StellarEvolution.org

Knowns and Unknowns

Motivation:

A Brief Historyof the Universe

Cosmic Dark Age`(after recombination)
Hubble Deep Field© Alexander Hegertime
What theBig Bang
made…

(The primordial abundance pattern)
Brian Fields (2002, priv. com.)(Pop III star yields)
Heger & Woosley (2010)
Frebel et al. (2005)What We
Find Today(The solar abundance pattern)
Lodders (2003)

Overview•Evolution of massive stars•The Stellar Zoo•Peculiarities of the different
mass regimes

Setting the Stage:

StellarEvolution

Once formed, the evolution of a star is governed by gravity:
continuing contraction
to higher central densities and temperatures

Evolution ofcentral
density andtemperatureof 15 MꙨand 25 MꙨ
stars

Nuclear(20burningstagesM stars)
ꙨFuel

Main SecondaryT
Product
Product(109 K)

HHeHeO, CCNe,Mg

NeTime(yr)MainReaction
CNO

N

0.02

107O, 22Ne

0.2106Na

0.8

103

12O, Mg

Al, P

1.5

320O

Si, S

Cl, Ar,K, Ca

2.0

0.8

Si,SFeTi, V, Cr,Mn, Co, Ni

3.50.021418s-process

4 H  4He
3 He4  12C
1220

C(α,γ )16O

C + 12C

Ne(γ ,α)16O

Ne( α,γ )24Mg

O + 16O

1628

Si( γ ,α)…

radiative envelope(blue giant)

net nuclear energy generation (burning + neutrino losses)

net nuclear energy loss (burning + neutrino losses)

total mass of star(reduces by mass loss)

convection

semiconvection

C shell burning

C shellburning

C burning(radiative)

He burning

H burning

convective envelope (red super giant)burning
NeOOOSiOSi

O shell burningMufti-Dimensional Convection(Meaken & Arnett 2007)

Multi-Dimensional Convection(Meaken & Arnett 2007)

Boom!

Bang!

Explosive Nucleosynthesis
in supernovae from massive stars

Fuel

Main SecondaryT
Product Product (109 K)

Innermost r-processejectaνp-processTime(s)Main
Reaction->10?

1(n,γ ), β −Niiron group>40.1( α,γ )O

Si, S

Cl, Ar,K, Ca

3-4

1

O, NeO, Mg, Ne

Na, Al, P

2-35p-process
11B, 19F,138
La,180Ta

2-35Si, O56

ν -process

516O + 16O( γ ,α)( γ ,n)( ν, ν’), ( ν, e-)He-dep
C-dep
Si-deppost-SN

He-ignC-ign
O-dep
pre-SN

25 MꙨ stars-processyields fordifferent
evolution
stages“Relocation” of the γ -process

γ -process can be made in implosive O shell burning, but peakabundance is destroyed by SN and recreated further out

destruction byn-exposure in
He shell

21 MꙨ star

The
StellarZoo?

Black Holesand GRBs fromRotating Stars(Yoon & Langer 2006;
data from Mokeim et al. 2006)

Rotation

Z=0.001

A small fraction of single stars isborn rotating rapidly
The fastest rotators evolve
chemically homogeneously,
become WR stars on the MS, andmay lose less angular momentum.

(Yoon & Langer 2006)

(Yoon et al. 2012)

Sana et al. (2012)

Evolution ofNon-Rotating
Singe Stars

Current Questions
Evolution of ...
• Lowest-mass supernova progenitors (Jones)• “Normal” massive stars• High-mass supernova progenitors (Yoshida)

Lowest-Mass
Massive Stars

Low-Mass Pre-SN Structure

Heger et al., in prep

z9.6

The Lowest Mass Core Collapse SNe(Poelarends, Herwig, Langer, Heger 2007)

Metallicity-Dependenceof Lower SN Mass Limit
Core masses forbigger stars are notaffected by this→ At [Z] = -2
the SN rateincreases by >25%
relative to solar, butwill drop for higher
metallicities.
(Ibeling & Heger 2013)

“normal”
massiveStars

12C Production
as a function
12of C(α,γ) and
3α reaction
rates

Carbon massfraction at the endof helium burning
depends thereaction rates andthe mass of the star~2000 stellarmodels(West+ 2013)

Deviations from solar production
12
as a function of C(α,γ) and 3α reaction rates
A “valley”of good
production
can befound –
somedegeneracy
in the rates,
though ashift in“reference”
massoccurs.
(West+ 2013)

Sensitivity of Structure to Initial Mass

Small changes in initial
mass can result in largechanges in progenitor
structure(Sukhbold+ 2013)

Sensitivity of “Compactness” to Initial Mass

There is a peak incompactness at around 20 MꙨ
initial mass

S: [Z] = 0
U: [Z] = -4
Compactness Parameter(Sukhbold+ 2013)(O'Conner & Ott 2011)

Sensitivity of “Compactness” to Codes

KEPELR and MESA show
noticeable differences indetail but general feature
can be reproduced if
physics parameters areadjusted accordingly.

S: [Z] = 0
U: [Z] = -4
(Sukhbold+ 2013)

Big Stars

Mass Loss due to Giant Eruptions?

Nathan Smith, 2007, First Stars III

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)?
●

The Most Massive Stars TodayR136●●●young massive starcluster
Age around 1.5 Myr
Star “a1”:maybe 200 MꙨ
initial mass

(Crother et al. 2010)

Ejected “metals”

PSN observed?
(Gal-Yam et al 2009)

Pair-SN Models(Kasen et al 2011)

SN 2001el (Ia)
SN 1999em (IIP)
SN 2006gy

Mixing in 250 MꙨ Pair-SN(Ken Chen 2011)

Chen 2013
in prep.

StellarForensics

➞Conclusions
The Evolution of Stars, especially of massive stars thatmake supernovae, is far from being a closed chapter.
●●●Uncertainties in Fates of massive stars also come fromuncertainties in their initial properties: mass, rotation, binarity

Significant uncertainty still exists in the modeling of the stellar
physics, including rotation, mixing processes, binary starevolution, and wind mass loss, but also uncertainties innuclear physics and key nuclear reaction rates matter.
Stellar forensics, determining abundance patterns of stellar
ashes, may be our best tool in the near future(e.g., constraints on pair-SNe)