Massive Stars:
Supernovae Then
and Now
“It is the stars, The stars above us,
govern our conditions”
King Lear, Act IV, Scene 3 and
Burbidge, Burbidge, Fowler, and
Hoyle, first page (1957)
John Poole and
S. Woosley (1983)
slide by Alex Heger
Stellar nucleosynthesis is easy.
It’s the ejection that is hard!
T3
25 M Presupernova Star
900 R 1R
H, He
He
Si, S, Ar, Ca
O, Mg, Ne
Fe
He, C
0.1 R 0.01 R
Hydrostatic equilibrium plus constant density imply:
dP GM
= P = NA k T
dr r μ
GM μ
Tc =
N A kR
1/3
3M
R=
4 If T for a given burning
stage is approximately a
Tc3
M2 constant, this suggests
that stars of higher mass
will burn at lower density.
Stars of higher mass will, at a given burning stage,
have higher entropy. They will be less degenerate.
Density Profiles of Supernova Progenitor Cores
These make the
heavy elements
These should be
easy to explode
2D SASI-aided,
Neutrino-Driven
Explosion?
The outcome of stellar evolution depends
upon four physical quantities
• Mass
• Metallicity
• Mass loss rate - related to metallicity
• Rotation (for today’s talk = 0)
And of course the physics and algorithms in the code
used to calculate it.
Woosley, Heger
and Weaver (2002)
Final States
Rotation = Zero
Binaries WD Ib Ic Faint SN Ibc
BH
Pulsational
Z 2 for A > 130
and absent for A bigger n/seed ratio.
Independent of metallicity…
.55 Proton mass fraction in the wind
(composite artist’s rendering)
.50
Early
Xp
.45
.40 Late
0 0.2 3 10
t(sec)
Early on e has a bigger flux (and the neutron is
heavier than the proton), so weak steady state in the
wind favors a proton excess - Xp > 0.50
Later the neutrino fluxes are similar but the e are
hotter. This makes the wind neutron rich - Xn = 1 - X p > 0.50
Neutrino wind
n-rich
Late times
site of the r-process
Woosley et al. (1994)
Late time solution,
independent of metallicity
S ~ 100 - 400 (not reproduced
since 1994)
Entropies in “realistic” models
are 3 - 4 times less.
Neutrino wind - p-rich
Pruet et al (2006) based see also Fröhlich et al (2006)
on SN models by Buras et al (2006)
Neutrino wind - p-rich
Variation of Entropy
Entropy x 2:
Xseed lower (n/s higher) S = 150, t = 2.15 s, T9 = 0.93
hence flow to higher Z.
<-140
S = 220, t = 0.58 s, T9 = 1.81
Entropy x 3: Flow to even
higher Z now passes
through valley of stability,
<-100
making “r,s” and “r-only”
nuclei in a p-rich
environment!
Loss of light p-nuclei.
26Al and 60Fe
M(60 Fe)/M(26 Al)
Predicted (Timmes et al 1995) 0.38 ± factor of 1.7
Observed (RHESSI, INTEGRAL, 2005) 0.29
Rauscher et al (2002) ~ 1.5 (few stars)
This survey with Rauscher rates 1.8
" with correct rates for 26 Al destruction 0.95
59,60
Still uncertain Fe(n, )60,61Fe, ?
22
Ne( ,n)25 Mg, rotation, WR mass loss
Nucleosynthesis
Outstanding Issues
• Entropy (or flavor mixing or time scale) for the
r-process
• Entropy for the -rp-process
• Cross sections and models that make 60Fe and
26Al consistently
• Some rare isotopes 44,48Ca, 47Ti, 64Zn, 92Mo
Lo Z
Low metallicity can affect the lives (and deaths) of
massive stars in five ways:
• The IMF may be different. In particular, more
massive stars may be created
• Mass loss will be reduced, though it is uncertain
* by how much. Because of this, the heavier stars are
harder to explode (and are different when they do
explode)
• The neutron excess available for nucleosynthesis
will be reduced, thus affecting the production of
odd-Z elements, neutron-rich isotopes, and the
s-process.
• Low Z stars are more compact, bluer presupernovae
• Rotation may be a bigger efect?
Eldridge and Vink (2006)
rotation reduces these limits
(Meynet and Maeder 2006)
Final States
Rotation = Zero
Binaries WD Ib Ic Faint SN Ibc
BH
Pulsational
Crab Pair
Z < Z /4 WD
SN SN IIp/87A SN IIp, BH Pair
SN
SN
Crab Common SN IIp, BH
Z WD Faint SN Ib/BH
SN SN IIp SN II-L
9 10 20 35 90 130
Here Z and binary membership are surrogates for mass loss
in single stars. Below ZO/4 we assume that stars complete their
evolution with at least some hydrogen still on their surfaces.
With some uncertainty about exact demarcations, one can
delineate four kinds of deaths for non-rotating helium stars.
(For rotation decrease main sequence mass 10 - 20%)
He Core Main Seq. Mass Supernova Mechanism
12 M 40 10 M 95 Fe core collapse to neutron star
or a black hole
40 M 60 95 M 130 Pulsational pair instability followed
by Fe core collapse
60 M 137 130 M 260 Pair instability supernova
M 137 M 260 Black hole. Possible GRB
Z = 0; 10 to 100 M
(Heger & Woosley, 2008)
Big Bang initial composition, Fields (2002), 75% H, 25% He
10 12 M M = 0.1M
12 17 M M = 0.2 M
Evolved from main sequence to
17 - 19 M M = 0.1 M
presupernova and then exploded
19 20 M M = 0.2 M with pistons near the edge of the
20 - 35 M M = 0.5 M iron core (S/NAk = 4.0)
35 - 50 M M= 1M
50 - 100 M M =5M Each model exploded with a
variety of energies from 0.3 to
126 Models 10 x 1051 erg.
1030 supernovae
low
metallicity
solar
He cores
CO cores Max M He
Solar ~12
Z=0 unlimited
Woosley, Heger, and Weaver (2002)
Low metallicity stars
are hard to explode
Solar
BE
Low
Metallicity
Mass
Joggerst, Heger, &
Woosley (2008)
Fallback in a 25 M Supernova
Blue - zero metallicity
Red - solar metallicity
Zhang, Woosley and Heger (2008)
Chevalier (1988)
Late time fall back is strongly
influenced by the reverse
shock which happens sooner and
is more pronounced if the
hydrogen envelope is compact.
Above 35 M
black holes form
in Z=0 stars
Zhang, Woosley, and
REMANT MASSES Heger (2008)
Z=0 Max n = 1.7 M Max n = 2.0 M
Av. n* M grav 1.33 ± 0.14 M 1.37 ± 0.20 M
Av. BH M bary 7.93 ± 7.47 8.52 ± 7.59
%n 47% 52%
% BH 53% 48%
Max BH 35.35 35.35
These are for 1.2 B explosions. An upper bound to the
black hole mass at any energy is about 45 solar masses
given by the maximum helium core mass.
Caveat: Primary nitrogen!
(Rotation dependent)
Primary N
Nucleosynthesis 10 - 100 solar masses
Z=0
“Standard model”, 1.2 B, = 1.35 (Salpeter IMF), mix = 0.1,
10 - 100 solar masses = 1.87
Best fit, 0.9 B, = 1.35, mix = 0.0158, 10 - 100 solar masses
= 0.748, (better).
Lai et al, (2008), submitted to ApJ, astroph 0804.1370
28 metal poor stars in the Milky Way Galaxy
-4 < [Fe/H] < -2; 13 are < -.26
E
Cr I and II, non-LTE effects; see also KE = E o (20/M) exp B
Sobeck et al (2007)
mixing 0.1 would have been "normal"
(Frebel)
Best single star fit
E = 0.6 B
21.5 M Mix = 0.0631
= 4.69
Best fit
Gaussian M= 15.0 ± 0.025 dex
1/2
M
E = 0.9 B Mix = 0.0063
20
= 2.74
25 M Pop III star
0.3 B, mildly mixed
Fe = 8 x 10 -6 M
Umeda and Nomoto, Nature, 422, 871, (2003)
Best Gaussian (Christlieb)
M = 17.0 ± 0.05 dex
1/2
M
E = 0.6 B Mix = 0.0251
20
= 1.84
Some general features low Z nucleosynthesis:
• Heavier remnant masses
• More fall back, less mixing
• Large odd-even effect in nucleosynthesis
• Primary B and F
• Above M ~ 40, primary N production
(M lower with rotation)
• No evidence for pair SN or hypernovae
Light curves:
• Typically faint with a maximum dominated by
radioactive decay (like SN 1987A)
• Above 40 solar masses, some are red
supergiants due to primary nitrogen production.
These will make more typical Type II-p
supernovae.
He Core Main Seq. Mass Supernova Mechanism
2 M 40 10 M 95 Fe core collapse to neutron star
or a black hole
40 M 60 95 M 130 Pulsational pair instability followed
by Fe core collapse
60 M 137 130 M 260 Pair instability supernova
M 137 M 260 Black hole. Possible GRB
Pair Instability starts at 80 solar masses
Primary N
pair
instability
110 M star with reduced mass
loss (M/5 on main sequence;
M/10 as RSG)
Final mass 74.56 M ;
ejecta SN 1
helium core 49.89 M
First explosion ejected H
envelope with KE SN II
= 1.4 10 50 erg
6.7 years later, a second
explosion, 7 10 50 erg,
runs into ejecta of the first
explosion at 2 1015 cm
The first supernova outburst is a
faint one, under 1042 erg s-1 lasting
about 6 months. Velocities are
typically under 1000 km s-1.
The second outburst is a
true “hypernova”, much
brighter than a SN Ia. Total
optical light is a few x 1050
erg.
About 8 years later the star
dies and may produce a
final supernova or even a
GRB.
Conclusions
• The known abundances in low metallicity stars
can be fit by “ordinary” supernovae in the 10 - 100
solar mass range. There is no need for “hypernovae”
or pair instability supernovae. Favored masses
are 10 - 20 solar masses. Explosion energies are
~ 1 B and less mixing is indicated.
• Metal deficient stars will produce many more black
holes with masses as high as 40 solar masses.
• Pulsational pair instability can give a wide range
of light curves, from the faintest to the brightest
observed supernovae. These objects can be
“supernovae” up to 6 times.
George Gamow in
My World Line