Sam M. Austin Mitchell 4/14/06 Supernovae, Their Collapsing Cores and Nuclear Physics Nature of...
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Transcript of Sam M. Austin Mitchell 4/14/06 Supernovae, Their Collapsing Cores and Nuclear Physics Nature of...
Sam M. Austin Mitchell 4/14/06
Supernovae, Their Collapsing Cores and Nuclear Physics
Nature of Supernova Progenitors
Their sensitivity to nuclear properties
How these properties are determined
Ongoing experiments
Sam M. Austin Mitchell 4/14/06
Evolution of Stellar Core for Heavy Stars
After initial formation
A gravitational collapse, interrupted by long nuclear burning stages.
Eventually form “Fe”core, and no further nuclear energy available.
Log Central Density
Log
Cen
tral
Den
sity
Woosley & Janke--Nature
Temperature vs Density
Sam M. Austin Mitchell 4/14/06
Problem since Baade/Zwicky in 1930’s suggested SN powered by gravitational energy from collapse of normal star to neutron-star
Supernova EvolutionThe special case of Fe
Previously products of f usion were lighter than the constituents, excess mass appeared as energy.
Fe is most tightly bound f orm of matter. Fusing two Fe takes energy, No more nuclear energy available.
Core collapses and keeps on collapsing
At about density of nuclei, collapse stops, bounces out. Resulting shock wave blows off the surf ace of star?
Huge amount of energy released, a suddenly bright star, a supernova.
“Fe”-Core Collapse
Bounce-Form Shock Wave
Shock--Dissociates Overlying “Fe”
Supernova EvolutionThe special case of Fe
Previously products of f usion were lighter than the constituents, excess mass appeared as energy.
Fe is most tightly bound f orm of matter. Fusing two Fe takes energy, No more nuclear energy available.
Core collapses and keeps on collapsing
At about density of nuclei, collapse stops, bounces out. Resulting shock wave blows off the surf ace of star?
Huge amount of energy released, a suddenly bright star, a supernova.
“Fe”-Core Collapse
Bounce-Form Shock Wave
Shock--Dissociates Overlying “Fe”
Supernova EvolutionThe special case of Fe
Previously products of f usion were lighter than the constituents, excess mass appeared as energy.
Fe is most tightly bound f orm of matter. Fusing two Fe takes energy, No more nuclear energy available.
Core collapses and keeps on collapsing
At about density of nuclei, collapse stops, bounces out. Resulting shock wave blows off the surf ace of star?
Huge amount of energy released, a suddenly bright star, a supernova.
“Fe”-Core Collapse
Bounce-Form Shock Wave
Shock--Dissociates Overlying “Fe”
"Fe" core Collapses
Bounce--Form Shock Wave
Shock moves out
Loses energy. Fe p's , n's in outer part of Fe core; neutrino emission
Stalls
Time
Supernovae Core Collapse—The Mechanism
Sam M. Austin Mitchell 4/14/06
Difficulty Of The Supernova Problem
A commentInsufficient knowledge of nuclear physics properties causes changes at the 1-few% level
Dangerous to assume that the effects are always cancelled by negative feedback processes
Nature of the energetics—the 1% problem?Only 1% of the available gravitational energy (1053 ergs) is emitted as explosion energy, rest as neutrinos. (Burrows argues it’s a 10% problem--90% of gravitational energy emitted prior to critical phase). But, either way, it may mean we have to do things very well.
What’s been tried
Delayed shock– re-energized by neutrinos from proto-neutron star Better neutrino transport, better weak interactions, 2 and 3-D (limitations), acoustic coupling, ……
Scheck, Janka
Sam M. Austin Mitchell 4/14/06
Triple makes 12C, 12C()16O turns it into 16O. Their ratio determines the amounts of C and O made and affects the nature of a star and of its iron core
An Example--Helium Burning
Rehm-ANL 10:10
WMU-MSU
Sam M. Austin Mitchell 4/14/06
SNII--Pre-collapse Fe Core Size
Pre-supernova evolution
Vary rate of 12C()16O (or Triple alpha)?
All else constant
Fe core mass changes by >0.2 M over the interesting range
Important?Naively, yes. If homologous core mass constant, need 3 x 1051 erg to dissociate extra 0.2 M to nucleons
Fe C
ore
Siz
e (
Sola
r M
ass
es)
0.5
1.0
1
.5
2.0
1.0 1.5 2.0 2.5 12C()16O Multiplier
or 1/Triple alpha?
25 MHeger, Woosley, Boyes
Need ratio of rates to 10%
() 160 ±40 keV b Brune 2006
3 alpha Fynbo 2006
Sam M. Austin Mitchell 4/14/06
Element Production in a Supernovae
Shell Burning
When He is exhausted in the core the core collapses, T increases, core carbon and oxygen burning begin. H and He burning in shells
The successive core stages are H He, gravity He C,O, gravity C,O Mg, Si--gravity, Si Fe.
How Sun Evolves
Hydrogen burning ends after 1010 yrs
Consumed central 10% of star
No heat source, pressure decreases and gravity wins. Core collapses, releases gravitational energy which heats the core.
Helium burning starts
Core gets hot enough to overcome Coulomb repulsion of two 4He (Z=2).
Helium fuses into 12C and 16O
Hydrogen consumed in a shell
He burning core T=108 K=107 kg/m3
H burning shell
Non-burning envelope
He Burning Core T=108 K = 107 kg/m3
The Result (Stellar Onion)
SN blows off outer layers Need detailed element distribution/abundances to predict SN element production
Sam M. Austin Mitchell 4/14/06
Detailed Models-Heger and Woosley 2001
It’s more complex than the onion even in 1D: M= 22 Msun. Along the x-axis sequential episodes of convective carbon, neon, oxygen, and silicon burning. Affected by rates of He-burning reactions.
Sam M. Austin Mitchell 4/14/06
SNII Nucleosynthesis A=16-40
12C()16O Multiplier (xBuchmann 1996)
Pro
duct
ion
Fact
or
Heger, Woosley,
Boyes
25 M
Explosion of 25 M star
Vary rate of 12C()16O
All else same
Production Factor“Same” PF for 1.2 x standard12C()16O rate
170 keV b
Sam M. Austin Mitchell 4/14/06
Weak Strength and Supernovae Core Collapse
Gamow-Teller (GT) Strength?
Mediates -decay, electron capture(EC), n induced reactions
GT (allowed) Strength S=1; L = 0, e.g. 0+ 1+; GT+,GT-
Lies in giant resonances
(n,p)
(p,n)
GT+ dominates process
Situation
After silicon burning, Tcore 3.3 x 109 K, density108 g/cm3. e- Fermi energy allows capture into GT+. Reduces e- pressure emits neutrinos. Speeds collapse.
At higher T, GT+ thermally populated, - decays back to ground state. - E.C.
Sam M. Austin Mitchell 4/14/06
Effects of Changed Weak Rates-Heger et al. Ap.J. 560 (2001) 307
2
4
6
8
T (
109
K)
T
4105106
Time till collapse (s)
10-8
10-7
10-6
10-5
10-4
10-3
dY
e
dt (
s1
)
LMP-ECLMP-
10010110210310
0.44
0.46
0.48
0.50
Ye
WWLMP
15 M
URCA
IPM vs Shell Model
WW standard Wallace-Weaver rates based on independent particle model (FFN)
LMP-from large basis shell model calculations. (Langanke and Martinez-Pinedo)
Significant differencesLarger, lower entropy "Fe" pre-collapse core More e-'s (Ye larger), lower T core. Larger homologous core
Sam M. Austin Mitchell 4/14/06
Important Electron Capture Nuclei
Pre-Collapse: Nuclei in the Fe-Ni region
Collapse: Heavier nuclei are important, including many with N>40
Sam M. Austin Mitchell 4/14/06
Do (N>40) Nuclei Undergo Electron Capture?
From Martinez-Pinedo
Independent particle model: No for N>40Transitions Pauli blocked
Shell model at finite T: Blocking removed—Has
important effects
Sam M. Austin Mitchell 4/14/06
Results of New Calculations--Langanke et al PRL
Nature of calculations
Shell model Monte Carlo + RPA
Results
Capture on nuclei dominates by x10
Neutrino energies are lower
Mass enclosed by the shock is smaller by 0.1 Msun
Shock is weaker
Ye varies with enclosed mass
Sam M. Austin Mitchell 4/14/06
Reliability of Nuclear Models for e-CaptureFor pre-collapse calculations
Quite good, some problemsFurther validation of models requires data for unstable isotopes especially odd-odd nuclei
: FFN (IPM)
: data (n,p) (TRIUMF)
: Caurier et al. (1999) Large basis SM : Caurier et al. folded with experimental resolution
?
?
?
(Caurier, et al NPA 653, 439(99
Sam M. Austin Mitchell 4/14/06
Reliability of Nuclear Models for e-Capture-cont.
For heavier nuclei--less firmly based and not validated
General Comment
Can’t measure everything, 1000s of transitions, many from thermally excited states
But need to do enough checks to have confidence in models
Nature of measurements: Hadronic charge exchange reactions
Operators similar to decay operator; (n,p), (d,2He), (t,3He) measure e-capture strength
B(GT) = CEX(q = 0)/unit , unit calibrated from known transitions
Accuracies in 10-20% range, better for strong transitions
Require energy of >100 MeV/nucleon to minimize 2-step processes
Reactions studied: In past (n,p), (d,2He), (t,3He); presently only (t,3He)
Sam M. Austin Mitchell 4/14/06
Charge Exchange Options
(t, 3He)Secondary triton beams 106-
7/sec at MSU/NSCL, 115 MeV/A tritons
Resol: 160 keV achievedData on 24,26Mg, 58Ni, 63Cu,
94Mo
90
0
10
20
30
40
50
60
70
80
0.0
MeV
1+
4.5
MeV
2-
7.7
MeV
1-
160 keV
12C(t,3He)12B
lab=0o1.7o
0
10
20
30
40
50
60
70
80
90
-2 0 2 4 6 8 10 12
0.0
MeV
1+
4.5
MeV
2-
7.7
MeV
1-
230 keV
12C(t,3He)12B
labo =1.7 3.4o
E(MeV)
Sherrill, et al
Counts
Unique beam-spectrometer(S800), simple analysis, calibration from (3He, t) reaction at Osaka. More beam nice
Future (Zegers, et al.)Develop techniques for using radioactive beams:
(p,n), (7Li, 7Be) in inverse kinematics to study -decay, electron capture, respectively. Test (7Li, 7Be) expt in near future.
Sam M. Austin Mitchell 4/14/06
(t,3He), (3He,t) vs (p,n) and Shell Model
Sam M. Austin Mitchell 4/14/06
II
Q2= -287 keV
+8Be
Hoyle state
Back to The Triple Alpha Process-More Formally
Step I: 8BeEquilibrium abundance of
8Be
Step II: 8Be + 12C(7.65)
Present Interests—3 and SNII (Iron core size, nucleosynthesis) 5% AGB Stars (Carbon production and carbon stars) 5% Limits on variation of “fundamental” constants
r3 rad(7.65)e-Q/kt
rad = + , -Q = Q1+Q2
Rate depends on properties of Hoyle state (7.65), mostly on rad
I
Q1 = -92 keV
Sam M. Austin Mitchell 4/14/06
How Well Do We Know rad
rad
2.7% 9.2% 6.4%2.7%
12%
Least well known quantity is
A WMU, MSU collaboration is undertaking a new measurement:
WMU Alan Wuosmaa, Jon Lighthall, Scott Marley, Nicholas Goodman
MSU/NSCL Clarisse Tur, SMA
Sam M. Austin Mitchell 4/14/06
Measuring A hard measurement: Branch is small ~6 x 10-6
New measurement: WMU/MSUWMU Tandem, (p,p’) at 135o, 10.56 MeV (strong resonance for 7.65 state)
pairs/#-7.65
protons)Aim: ± 5% accuracy
PMPM
PM Si, 1 of 4
PMPM
PM
PMPM
PM Si, 1 of 4Side View
Top ViewPM
PM
PMPM
Plastic Scint
Liner
12C Target
BeamPM
PM
PMPM
Plastic Scint
Liner
Beam
Improved version of Robertson, et al PRC 15,1072(77)
Sam M. Austin Mitchell 4/14/06
WMU-MSU/NSCL Detector
Sam M. Austin Mitchell 4/14/06
Final Comments
Discussed two cases were nuclear uncertainties are important
Helium burning (expts on 12C( and 3alpha rates ongoing)
Electron capture (expts ongoing)
Others have not been much investigated12C+12C reaction rate poorly known—sensitivity of progenitor structure?r-process nucleosynthesis could provide a diagnostic of conditions at its site—nuclear properties need to be better understood
Sam M. Austin Mitchell 4/14/06
Cocktail beam
78Ni
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
70 120 170 220
Mass (A)
Ab
un
da
nc
e (
A.U
.)
Observed Solar Abundances
Model Calculation: Half-Lives fromMoeller, et al. 97
Series4
Measured half-life of 78Ni with 11 events Acceleration of the r-process
excess of heavy elements with the new shorter 78Ni half-life
Result: 110 +100-60 ms
(Theory: 460 ms)
T1/2 measurement at NSCL
Beta Lifetimes are important--Example: doubly magic 78Ni
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
70 120 170 220
Mass (A)
Ab
un
da
nc
e (
A.U
.)
Observed Solar Abundances
Model Calculation: Half-Lives fromMoeller, et al. 97
Same but with present 78Ni Result
En
erg
y los s
velocity
r-process calculation
P. Hosmer et al. 2005 (NSCL, Mainz, Maryland collaboration)
Sam M. Austin Mitchell 4/14/06
Some Comments
Discussed two cases were nuclear uncertainties are important
Helium burning (expts on 12C(a,g) and 3alpha rates ongoing)
Electron capture (expts ongoing)
Others have not been much investigated12C+12C reaction rate poorly known—sensitivity of progenitor structure?r-process nucleosynthesis could provide a diagnostic of conditions at its site—nuclear properties need to be better understood
2D and 3D calculations of progenitor evolutionIn their beginning phasesWill surely change the nature of the pre-SN starNote: present 1-D models differ somewhat from group to group