Why (Core-Collapse) Supernova People like SNSschol/sns_workshop/talks/hix.pdf · 2012. 5. 3. · W....
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Why (Core-Collapse) Supernova People like SNS Sk 202-69 SN 1987a W.R. Hix (ORNL/UTK)
Transcript of Why (Core-Collapse) Supernova People like SNSschol/sns_workshop/talks/hix.pdf · 2012. 5. 3. · W....
Why (Core-Collapse) Supernova People
like SNS
Sk 202-69SN 1987a
W.R. Hix (ORNL/UTK)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
SN 1987a
1045 W
Observing Supernova Neutrinos
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Ejecta Rich in Heavy Elements
Hughes, Rakowski, Burrows & Slane 2000
Supernovae from Massive Stars produce most of the elements from Oxygen through Silicon and Calcium and half of the Iron/Cobalt/Nickel. They may also be responsible for the r-process.
W. R. Hix, ν@SNS, Oak Ridge, May 2012
A Core-Collapse Supernova is the inevitable death knell of a massive star (~10+ M☉).Once central iron core grows to massive to be supported by electron degeneracy pressure, collapse ensues, accelerated by electron capture.Shock forms when nuclear matter appears, creating a neutron star.
Textbook Supernova Hillebrandt, Janka, Müller, Sci. Am. (2006)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Anatomy of Explosion
ShockSi Layer
O Layer
IronCore
25 M☉ GRResolutionr,θ: 256a, 256ν energy: 20
Time (s)
Avg Atomic Mass
Radi
us (k
m)
1D Shock
Gray Shock
W. R. Hix, ν@SNS, Oak Ridge, May 2012
For the first 150 ms after bounce, the supernova is essentially spherical. Once the Standing Accretion Shock Instability (SASI) and neutrino-driven convection begin, the shock is deformed and gradually progresses outward in radius.
SASI in Action
~0.5 Million CPU Hours on
256 proc.
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Neutrino Interactions
e±/ν capture on nucleons and ν-nucleon elastic scattering + recoil & relativity (Reddy, Prakash & Lattimer 1998)
+ weak magnetism (Horowitz 2002)
+ correlations (Burrows & Sawyer 1997, Reddy, Prakash, Lattimer & Pons 1999)
ν-electron scattering / pair production / νν annihilation + νeνe ⇔ νµ νµ (Buras, Janka et al 2003)
+ Bremsstrahlung (Hannestad & Raffelt 1998, Thompson, Burrows & Horvath 2000)
+ Plasmon decay (Schinder & Shapiro 1982)
e-/ν capture on nuclei and ν-nucleus elastic scattering + Inelastic Scattering (Bruenn & Haxton 1991, Juodagalvis et al. 2004)
+ Electron capture (Langanke & Martinez-Pinedo 2000, Langanke et al. 2003)
Bruenn (1985) and improvements
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Captures on NucleiEntropy of iron core is low (S/k ~1) so few free nucleons are present. Thus e- and ν capture on heavy nuclei via f7/2⇔f5/2 GT transition should dominate. (Bethe,Brown, Applegate & Lattimer 1979)
During collapse, average mass of nuclei increases, quenching e- capture (at N=40) in IPM. Thermal unblocking and first forbidden were considered but rates were too small. (Fuller 1982, Cooperstein & Wambach 1984)
106 108 1010 1012 10140
1
10
100
0
1
10
100
Density (g cm-3)
En
erg
y (
Me
V)
Ye
kT
e
AE e
A (N
ucle
on N
um
ber)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Which Nuclei are Present?
Neutron-Rich Nuclei with A ≤ 120 are present in collapsing core.
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Because capture rates on heavy nuclei → 0 under IPM, captures on protons were thought to dominate.Beyond IPM, Shell Model Diagonalization calculations could provide the answer but are limited to A<65. Langanke et al (2003) employed a hybrid of shell model (SMMC) and RPA to calculate a scattering of rates for A<110. Electron/neutrino capture on heavy nuclei remains important throughout collapse.
Beyond IPMLanganke, …, Hix, … (2003)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Can we measure e-/ν Capture?Charge Exchange Reactions, like (n,p),(d,2He),(t,3He), also sample Gamow-Teller strength distribution, providing strong constraints on structure models.Current Experiments, on stable nuclei, agree well with shell model calculations for A<60. For A=80-100, nuclei of interest are 2-6 neutrons richer than stability and should be achievable with NextGen RIBs.
Baümer et al. PRC 68, 031303 (2003)
But these measurements don’t tell us about weak reactions.
W. R. Hix, ν@SNS, Oak Ridge, May 2012
The impact of e- CaptureContinued electron capture in the core lowers Ye, which changes the initial PNS mass by 20%.Reduced electron capture in the outer layers slows the infall, reducing the ram pressure opposing the shock reducing the long term impact in 1D.Juodagalvis, Langanke, Hix, Martínez-Pinedo, & Sampaio (2010) recently published an improved tabulation of nuclear electron capture for use in SN models.
15 M☉
Hix, Messer, Mezzacappa … (2003)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Neutrino Changesνe burst slightly delayed and prolonged.15% boost in νe luminosity over 50 ms after bounce, other luminosities minimally affected (~1%). Mean ν Energy altered:
1-2 MeV during collapse~1 MeV up to 50ms after bounce~.3 MeV at late time
In total, this changes the maximum excursion of the shock by 10 km, occurring 30 ms earlier.
Hix, Messer, Mezzacappa … (2003)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Supernovae Nucleosynthesis
Time
Radi
us
Heating
Cooling
Infall Shock
Wind
Intermediate mass elements
ν-process
p-processr-process
Shock ejection
NeutrinosIron-Peak elements
Bruenn
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Despite the perceived importance of neutrinos to the core collapse mechanism, models of the nucleosynthesis have largely ignored this important effect.Nucleosynthesis from neutrino-powered supernova models shows several notable improvements. 1) Elemental abundances of Sc, Cu & Zn closer to those observed in metal-poor stars.2) Over production of neutron-rich iron and nickel reduced.3) Potential source of light p-process nuclei (76Se, 80Kr,84Sr,92,94Mo,96,98Ru).
Neutrinos & Nucleosynthesis
Fröhlich, … Hix, … 2006
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Putting the ν in νpSupernova ejects proton-rich (Ye > 0.5) gas at high temperature (~ 10 GK), composed of free neutrons and protons. Cooling produces a p-rich and α-rich freeze-out. Once temperature drops below 3 GK, free protons can capture on iron-peak species.Slow β decays (e.g. 64Ge) would stop this process but (n,p) and (n,γ) “accelerates” β decays. Protons converted to neutrons via
anti-neutrino capture.
Fröhlich, … Hix, … (2006)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
νp-process
Our preliminary results show proton-rich ejecta and νp-process (dotted lines), but more weakly than previous results.
Time (sec.)
Mas
s Fr
actio
n
Lee Ph.D. (2008)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Supernova DetectionNeutrinos allow direct observation of the proto-neutron star, revealing information otherwise unavailable.Measuring Relative Flux will reveal important data like the time of explosion (when accretion stops) but luminosity tells us much more about the structure of the PNS and the accretion rate.Optical observations will reveal distance to within 10%, leaving neutrino detection cross sections as the largest uncertainty.
Burrows, Klein & Gandi (1992)
W. R. Hix, ν@SNS, Oak Ridge, May 2012
SNS looks like a mini-CCSN, producing many neutrinos of tens of MeV.This allows an experimental program to measure neutrino cross sections of interest for supernovae.
~1015 ν sec-1
Homogeneous detector for Liquid targets 2H, 12C, 16O, 127I
Segmented detector for Solid targets 51V, 27Al, 9Be, 11B, 52Cr, 56Fe, 59Co,
209Bi, 181Ta
Why (Core-Collapse) Supernova People like SNS?
W. R. Hix, ν@SNS, Oak Ridge, May 2012
Exchange of ντ⇒νe could have beneficial effect by increasing mean neutrino energy and therefore the heating rate.Measured mass difference implies oscillations occur well above heating region.More exotic scenarios (e.g. active-sterile or active-active) remain under investigation.Mezzacappa & Bruenn 1999
Neutrino Oscillations?
