Cosmological Aspects of Nucleosynthesis
1. Comments on the Big Bang Nucleosynthesis (BBN)
2. Observing heavy elements
3. Heavy-Element Nucleosynthesis beyond the dark age, or
Nucleosynthesis in stars
I am not presenting a paper
no time for a lecture.
It remains to try to describe a scenario
Mounib El Eid
American University of Beirut
Department of Physics
Sinaia, Romania June 2012
1
Thermal History of the Universe
Event
Plank Time/
Graviton
decoupling
Time/Energy
10
 43
GUT/Inflation
10
EW Unification
10
Quark- Hadron
transition
ν- decoupling
e annihilation
10
13
s / 10 GeV
 34
 12
5
14
s / 10 GeV
3
s / 10 GeV
s / 200 MeV
0 . 2 s /( 1  2 MeV )
1 s / 0 . 5 MeV
200 s  300 s
Nucleosynthesis
0 . 05 MeV
Matter-radiation
equality
Recombination
Photon
decoupling
Description
Non-perturbative quantum gravity dominates, GR
is not valid, current research
Main uncertainty is matter composition/SUSY
Electroweak symmetry/ massless bosons
Free quarks and gluons become confined within
baryons(3quarks) and mesons (quark, anti-quark)
Neutrinos decouple/ratio of neutrons to protons
freezes out
Small excess of electrons over positrons
Nuclear reactions/ free protons and neutrons
form helium and other light elements
11
10 s / ~ eV
12
10 s / 0 . 4 eV
10
13
s / 0 . 3 eV
Helium then hydrogen recombination
Everything becomes neutral and thus photons
decouple from matter
2
Thermal History of the Universe
3
Why did the
density of dark
energy became
larger the density
of matter 5 billion
years ago?
If the dark energy is
due to a cosmological
constant, its average
mass density remains
constant. The
consensus model
predicts dark-energy
dominated universe
about 5 billion years
ago.
4
Big Bang Nucleosynthesis (BBN)
Argument in favor of BBN
1. The question is: why is approximately one-quarter of the mass of the universe
is in the form of helium
2. Cosmic abundance of He too high to be made in stars, since not enough
mixing to the surface.
3. Helium survives in the early universe, because the density of the expanding
universe becomes too low to burn helium
4. Nuclei of mass number A=5 and 8 are unstable, and this limits the BBN to
the light elements:
(D,3He, 4He, 6Li, 7Li, 7Be)
5. Under the assumption of homogeneous baryon density the BBN depends
on one parameter
 
nB
n

baryon number
photonn
denity
umber density
In other words,  is the only parameter, since n is determined by the
Micro Wave Background
5
1. The Standard Big Bang Nucleosynthesis (SBBN)
Occurs in a radiation-dominated universe
Assumptions:
(1) Standard Particle Physics
(2) Cosmological Principle: (Universe isotropic and homogeneous)
(3) Geometry described by the Robertson-Walker metric
ds
2
 dt  a (t){
2
2
dr
2
 r (d θ  sin θ
2
(1  kr )
2
2
2
2
dφ )}
a(t) scale
factor absorbs
the dynamics
(4) Expansion of the Universe described by the Friedmann's equation
H
2
 . 
a 

 a 
 
=cosmological constant
2

8
3
 G 
k
r
2

1
3

  1 closed

k  0
flat
  1 open






6
CRITICAL DENSITY
c 
3H
2
8 G
 1 . 88 x 10
 29
h0
2
g.cm
-3
 0
k  0
h0  H 0 /( 100 km / s / Mpc )
H0 
H 0  73 km / s / Mpc
Present Hubble
constant
(WMAP)
Means: if a galaxy is at
100 Mpc away from us,
It will be moving at
7100 km/s
Cosmological parameter=baryon density/critical density (C)
N 
N
C
 3 . 6 10
3
2
h 0  10
 T 


 2.73 
3
 10  10 ( n b / n  )
10
7
RESULTS of BBN
 Most of the nucleosynthesis
took place at about 1.2x109 K.
At larger temperature, D would
be destroyed by radiation
background


4
He / H  0 . 25
4He
mass fraction:
0.23 to 0.25 traces of
D, 3He, 7Li, 7Be

D / H  1 . 2  10
5
No nuclei were formed
before 10 s because of the
deuterium bottleneck
See next slide
At about 1000 s, T<4x108 K, no nucleosynthesis was possible any more. The free
neutrons declined and decayed into protons, electrons and antineutrinos.
8
Simplified network for BBN
Deuterium is a bottle neck
9
 Abundances of D and 3He
Figure Fig. 19.10 Longair
provide strong constraint on
present baryon density, while
that of He is remarakably
constant
 D-abundance very sensitive to
the baryon density (B), while that
of He almost constant.
Reason: He-abundance determined
from equilibrium abundance of
neutrons and protons. Abundance
of D depends on number density of
nucleons. D sets upper limit on B
observations
10
Result
2
 B h 0  0 . 015
h0 
H0
1
km s Mpc
1
100
Even with
h0  0 . 50
 B  0 . 06
Baryonic matter cannot close he
universe and cannot account for the
amount of dark matter
Remarkable result of the BBN:
3 neutrino families
More than 3 neutrino-families would have contributed to the mass density of ultrarelativistic particles. This would have speeded up the expansion in the radiationdominated universe. Neutrino would decouple at higher temperature and Helium
would have been overproduced.
Agreement with elementary particle physics is achieved; 3 neutrino families
11
obtained from the width of the decay spectrum of Z0 boson.
Dark Age
A challenge
in modern
cosmology
is to
understand
how the
cosmic dark
ages ended.
12
Timeline of light in the universe
WMAP data indicate:
The oldest light we can see today is
Galaxies formed
Some
400
million
years
later
at
the cosmic background radiation .
more recently
z=11
the
first
stars
appeared
.
It came from the time 380,000 yrs
and can be seen
They
re-ionized
the
universe,
after Big Bang when the universe
at visible
and
their
light
was
shifted
to
became transparent. This light had a
wavelength.
infrared
wavelength
.
redshift of z=1100 and appears in
the microwave
Dark ages: era from recombination (at 380,00 yr) to the first stars at 400 million yr. This
dark ages ended when the universe was filled for the first time with light from stars
13
Using Wien’s law:
(  max ) 0
(  max ) rec
z 

T rec
T0
 rec   0
 rec

3000 K
 1100
2 . 75 K

1 z 
0
 rec
z  1100
14
2. Observing heavy elements
Talking about galaxies we mean near-field cosmology , while the high
red shift universe is associated with the far-field cosmology
 Large dispersion in metal
abundances [X i /Fe] in particular for
the n-capture elements
Light s-process
 s-process elements:
Sr, Zr, Ba, Ce, La, Pb
Formed during quiescent phases of stellar
evolution: He-burning in AGB stars and
massive stars
 r-process elements:
Heavy s-process ?
Sm, Eu, Cd, Tb, Dy, Ho
Cannot be formed during quiescent phases of
stellar evolution, but mainly in SNe explosion.
r-process
r-process elements measured from stellar
atmospheres reflect conditions in the progenitor
cloud
Metallicity
[ A / B ]  log( N A / N B ) *  log( N A / N15B ) sun
Summary of this part
Observations of nucleosynthetic signatures of metal-poor stars represents a
cornerstone of near-field cosmology.
A success in this direction requires improved stellar models, especially of
SNe, and nuclear/atomic data and realistic galaxy formation models
 The relative r-process and alpha-element abundances for metal-poor stars will
constraint the yield for different stellar masses and associated mass cuts in SNe.
Here are some thoughts by Freeman and Bland-Hawthorn (2002)
The near-field universe is as important as the far-field universe for understanding
galaxy formation and evolution.
 Understanding galaxy formation is understanding baryon dissipation within the
CDM hierarchy, or understanding the formation of disks.
 A great advantage of near-field study is to derive ages and detailed
abundances of individual stars within galaxies and the local group.(Gaia
sphere)
16
r-process rich star CS22892-52 show some interesting results
Sneden eta al: APJ, 591, 936 (2003)
A similar case is CS31082-001 (Hill et al. 2002)
Weak r-process
Z= 56
Main r=process
r  process
rich :
[ Eu / Fe ]   1 . 6
EMP: [Fe/H]=-3.1
remarkable
n-capture elements
with Z56 in this
metal-poor star match
closely solar system rprocess pattern
Also remarkable
Scaled solar rprocess distribution
does not extend to the
lighter n-capture
elements below Z=56
log  ( A )  log( N
A
/ N H )  12 . 0
For example: Silver
(Ag, Z=47) is deficient
17
Conclusion from previous Figure:
It seems that the r-process could be divided like the s-process into 2 components :
weak r-process ( so far it is called LEPP=Light Element Primary Process)
main r-process (classical r-process)
Heavy elements have been also observed in extremely metal-poor stars
with [Fe/H]=--5:
HE 0107-5420 and HE1327-2326
Both are rich in CNO but very poor in n-capture elements. This is different
from the previous cases (CS 22892-052 or CS31082-001)
Learn effect
Rapid change in nucleosynthesis in the early phase of the Galaxy.
It seems: first stars were massive able to produce CNO elements
but not the heavy n-capture elements
18
r-process rich versus r-process poor
r-process rich: [Eu/Fe]=+1.6
r-process poor: [Eu/Fe]=-0.5
19
r-process throughout the Galaxy
16 stars
The difference between BD+173248 and HD122563 discussed above is found
to be a general behavior as shown in the following Figure:
r-process rich
flat
Nothing
here
HD122563
r-process poor
No heavy
n-capture
elements
References to this Figure: Cowan eta l (2011) preprint
20
The abundances in HD122563 suggest an incomplete rprocess, or let us say an n-capture process with a neutron
density between 1020- 1024 cm-3, since the synthesis of the
heavy n-capture elements needs 1024 – 1028 cm-3
In the following some results by Kratz et al (2007):
r-process rich: [Eu/Fe]=+1.6
Flat
Sneden et al. (2003)
Honda et al. 2006)
Abundances
gradually
decrease with A
r-process poor: [Eu/Fe]=-0.5
21
Barium Isotopes in extremely meta-poor massive stars
Barium Isotopes in the meta-poor subgiant HD 140283 :
( [Fe/H]=-2.6, [Ba/Eu]=-0.66 and [Eu/H]< -2.8 (r-poor)
Pure r-process
Pure s-process
Author
f
odd
f odd  [ N (
Magain (1995)
0 . 08  0 . 06
Ghallagher et al. (2010)
0 . 02  0 . 06
Lambert et al (2002)
135
Ba )  N (
137
Ba )] / N ( Ba )
Purley s-process signature
0 . 30  0 . 21
22
Different mixture of odd and even isotopes are produced by the r-process and sprocess .
In particular, 134Ba and 136Ba are produced only by the s-process due to the
shielding by the Xenon isotopes 134Xe 136Xe made by the r-process.
Z=56
Shielding Ba
Z=54
23
Conclusions from observations
 clear presence of n-capture element in atmospheres of metal-poor stars
and globular cluster stars
The comparison between r-process rich ([Eu/Fe]> 1.0) and r-process poor
([Eu/Fe] < 1 indicates :
abundances of the heavy elements (Ba and above, Z=56)
consistent with solar system r-process distribution. This seems
to be the main r-process.
The distribution of the lighter (Z<56) n-capture elements is not
conform to solar pattern. New detection of Pd, Ag, Cd (Z=46,
47,48) suggest a weak r-process not yet identied:
LEEP
-p process in core collapse SNe
High Entropy Wind in core collapse SNe
Exotic mixing in late phases of massive EMP stars
Do different mass region (Ge, Sr-Zr, Pd-Ag-Cd) require different processes?
24
3. Making the Heavy element in Stars
Heavy elements beyond copper are formed
by 2 neutron-capture processes:
s-process
1/2
s for slow, but what is slow?
Slow is the n-capture
compared to beta-decay
Main component
A > 90,
AGB stars:
(1-8) Msun
Main component
A < 90, Massive stars,
M15 M Sun
Secondary process:
Depends on iron seed-abundance
r-process
r for rapid, but what is
rapid?
neutron capture
compared to beta-decay
Standard scenario:
Core collapse SNe
M >8 Msun.
Consistent model not yet
available
Primary process:
built up from scratch as
Taka Kajino emphasized
25
Basics of the s-process
Seed nucleus:
Neutron source
Neutron spectrum
Temperature range
Time scale
Iron
13C(,n)16O
AGB stars
22Ne(,n) 25Mg
Massive Stars
Maxwell-Boltzmann Distribution (details later)
(25 – 30) KeV or (1.5 – 3.5) x 108 K Helium Fusion
( 90 – 100) KeV or (1.04-1.16)x 109 K Carbon Fusion
 n   
 n  
Where?


Beta-decay much faster, Helium fusion
Comparable time scale: carbon fusion
Massive Stars
Thermally pulsating stars (AGB stars
26
Some Details of the s-process ( Ns – curve)
The s-process works with thermal neutrons. They undergo elastic scattering in the star’s
plasma.
The neutrons obey the Maxwell-Boltzmann distribution (MBD):
 ( v )  4 v (
2
m
2  kT
)
3/2
2
e
 m v / 2 kT
From lab experiments, we know that the neutron-capture cross section varies like:

n

1
vn

1
En
S-wave scattering
0
MBD
E0 =most probable energy
E0=kT
En
27
Where the s-process?
28
In AGB Stars
Where in HR diagram
“Cat Eye” planetary nebula
after the AGB phase
Asymptotic
Giant Branch
White dwarf
29
s and r –processes in Z-N diagram
Cd
Ag
Pd
Rh
50
82
126
magic numbers
30
r=process in Supernovae?
Cassiopeia A
SPITZER image
of Cassiopeia A
10,000 lyr away
15 lyr across
The above image is a composite of X-ray, optical, and infrared light exposures that
have been digitally combined. The infrared light image was taken by the orbiting
Spitzer Space Telescope and was used in the discovery of the light echo. The
portion of Cassiopeia A shown spans about 15 light years and lies 10,000 light
31
years away toward the constellation of Cassiopeia.
Log nn=20-22
Log nn=20-24
Log nn=20-26
Log nn=20-28
32
The world of stars
(1  8 ) M
Sun
AGB
8  140
Iron core collapse
Shock/neutrino
driven
Planetary
Nebula
White Dwarf
Neutron stars
Black holes
 140  260
 260
Massive C/O
Cores: 64- 133 MSun
Explosive oxygen
burning
Pair Creation
Supernovae
Black holes
33
The Central Evolution of Stars
ElectronPositron –
Creation.
Pair Creation
supernovae
25
TEMPERATURE
(K)
Non-degenerate
Iron
Disintegration
Core collapse
supernova
AGB stars
White Dwarfs
DENSITY ( g/cm3)
Rapid
Electron
Capture
Core
collapse
Supernva
34
First stars (pop III)
If very massive they undergo pair creation supernovae
35
What is a Pair Instability Supernova (PCSNe)?
PCSNe:
final state evolution of a very massive stars
which develops a very massive carbonoxygen cores largely supported by
radiation pressure
Evolution of such cores proceeds toward
higher temperature and relatively low density
such that electron-positron pairs are created in
equilibrium by the radiation field according to
2  e

 e

Although the mean energy photons is about
kT, there are enough photons in the tail of
the Planck’s distribution that can create
these pairs even at 109 K
Temperature-density profile
T- profile for a 112 Msun star at time reversal
of the collapse. Note that significant part of the
core is inside the instability region.
Details in:
Ober, El Eid & Fricke: A&A , 119, 61 (1983)
36
Why does <4/3 has a finite range?
The decrease of  below 4/3 is a consequence of the new particles which
do not immediately add their contribution to the total pressure..
At high densities: >4/3, because the electron becomes more degenerate
At high temperatures: >4/3 because the particles become relativistic such that
the energy gap for pair creation is no more important
37
The PCSNe are usually associated with early stars, or Pop III stars
Is there any evidence of this unusual supernova type?
The observations of the SN 2007bi ( Gal-Yam et al, Nature ,462, 624, 2009) in a
dwarf galaxy argue for this with an estimated core mass is about 100 MSun
Another object is SN2006gy (Smith et al , ApJ 666, 1116 (2007))
Light curves of super luminous SNe
Gal-Yam et al (2009)
R-band light curve of SN2007bi. With
a peak magnitude of -21.3 mag
If this light curve is radioactively driven,
> 3 Msun of 56Ni are needed. The slow
rise time (70 days) and photospheric
velocity of 12,000 km/s indicate an
exploding very massive object of about
100 Msun and very high explosion
energy > 1052 erg
38
Implication of the discovery of SN2007 bi
 The estimated high core mass is in conflict with the commonly used mass loss
rates as a function of metallicity
 Regardless the correct description of mass loss, the data indicate that an
extremely massive stars (>150 Msun ) are formed in the local universe in a dwarf
galaxy with a metallicity
12+log[O/H]=8.25 (less than 1/10 of the Sun’s metalicity
Can the dwarf galaxies serve as fossil laboratories for studying the earl universe?
 Future missions like the
NASA’s James Webb Space telescope
will help to estimate the contribution of these events to the chemical evolution in
the early universe.
39
Nucleosynthesis in PCSNe
Updated calculation by Heger & Woosley (2002) yield:
 No heavier elements than Zinc, no r-process, no s-process
 Mainly products of explosive oxygen burning. Even nuclear charges (Si, S, Ar, Ca,, ...)
in almost solar distribution
 Element of odd nuclear charges (Na, Al, P, V, Mn,...) are deficient. The explanation of
this is because the massive C/O massive evolves almost directly to oxygen burning
without creating a neutron excess
Production factors of C/O cores of
masses 64 to 130 Msun which
undergo PCSNe, with different
assumption of the exponent of a
Salpeter-like IMF
40
Exotic n-capture scenarios
Massive extremely metal-poor stars
(1) Zero-age mains sequence shifted to higher effective temperature as Z decreases.
This is a consequence of reduced metallicity.
Recall that the energy generation via the CN cycle:
(  ) CN  8  10
27
(  ) CN  (  ) CN T
(  ) pp   ) CN T
 x H x CN T 6
2 / 3
e
 152 . 3 / T 6
1/ 3
17
4
At T=25x106 K
At T=15x106 K
Lacking of heavy elements, the star has to contract and heats up to burn hydrogen at
high temperature.
(2) As consequence of the compactness of the star , it cannot evolve to become
red giants. They remain confined to the blue part of the HR diagram, when
Z<10-3 . As seen on next page, the hydrogen-burning shell remains
convective all the time.
More details are found in :
El Eid, The , Meyer
Space Sci. Rev. , 147, 1-29, 2009
41
El Eid, The , Meyer
Space Sci. Rev. , 147, 1-29, 2009
Many references there
25 Solar mass star
Z=10-6
For initial z  10
3
This stays in the blue. Only with
significant amount of rotation can
such a star evolve to red super
giant stage. Even wit rotation, only
a small fraction of time is spent in
the red part
Z=10-3
Z=0.02
the stars do not evolve to red giant branch.
42
Solar-like
composition
Not here
Convective
hydrogenburning
shell
survives
43
Next exotic scenario: double Shell flash in massive stars
Beyond core Helium burning
Possible merging of the convective
H-burning shell with the He-burning shell
Carbon mixed with protons so that the reaction
13
C ( , n )
16
O
The, El Eid , Meyer: in prep.
Is activated as a neutron source
44
Result after one time step of proton mixing into the helium convective shell.
Strong enhancement near Z=38 -48
45
Another scenario: with ROTATION
Pignatari et al. , ApJ, 687, L95, 2008
25 Msun with [Fe/H]=-3, -4 not smaller
Basic Scenerio:
Neutron source
22
Ne ( , n )
25
Mg
Primary source, since in this scenario Carbon is mixed by rotation to the convective
H-burning shell creating 14N which is mixed down to the Helium burning core.
In this way an s-process operates near the end of core Helium burning
The say they produce nuclei up A=130
Why is the 13C source is not activated??
46
Final Words
 Evolution of early stars linked to nucleosynthesis of heavy elements turns out to be
a link to Near-field cosmology (understanding galaxy formation); It is a challenging
topic and a revival of the importance of stellar evolution as a fundamental
cornerstone of modern Astrophysics
 The evolution of the neutron-capture elements traces back the chemical
evolution of the galaxy and is bring us back to the dark ages where in order to
become more enlightened and remove the darkness of our ignorance
47
Does this game work?
We need his optimism like this star from FC Barcelona
(and FC Libya) to get an answer
JJ with American muscles
48
OR
am I dreaming
He shaved
himselfafter he
has seen this
photo
49
Final entertainment
Nustar
http://science.nasa.gov/science-news/science-at-nasa/2012/15jun_nustar/
Why supernova is not happening on computer?
50
Thermal velocity of the neutron:
1/ 2
 2m 
vT  

 kT 
Due the the above energy dependence:
 v  constant
  T vT
 v

Let:
  
,
  v 
vT
Then:
 T   (vT )
 ( v ) ( v ) d v
Maxwell folded
0
for   1 / v
 T

    2
2
(
)

for


1
/
v
T

 





Implication: measurement of  near vT very useful.
51