Introduction to Computational Nuclear Astrophysics with Two...
Transcript of Introduction to Computational Nuclear Astrophysics with Two...
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Introduction to Computational Nuclear Astrophysics with Two Exemplary Codes
: FLASH and MESA
Kyujin KwakKorean Astronomy and Space Science Institute
(KASI)2nd Dogye Workshop on
Nuclear Physics and Nuclear Astrophysics
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Outlines
• Motivation– Introduce computer codes that model connections
between nuclear physics (both experiments and theory) and observations
• Introduction– Nuclear Physics for Astronomy– Observations/Astrophysical Phenomena: stars/stellar
evolution, novae/supernovae, X-ray Bursts, gamma-ray bursts, neutron stars
• Two Example Codes: FLASH and MESA
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Nuclear Physics for Astronomy
from http://www.phy.ornl.gov/hribf/science/abc/
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from http://radchem.nevada.edu/
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Stars
From http://www.jca.umbc.edu/~george/html/courses/
Hipparchus Observations
Image from Greg Bothun
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Novae
• H and He accreted from a companion star onto a white-dwarf go through nuclear burning and explodes producing a bright flash of light.
• If the total mass of accreted material plus the original WD is larger than Chandrasekhar limit, it explodes as a supernova (Type Ia) rather than a nova.
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Supernovae
• Observations
– Type I: No Hydrogen
– Type II: Hydrogen
• Progenitors
– Type I: detonation of NS in the binary
– Type II: core collapse of a single star
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Supernova taxonomy
Type INo hydrogen
Type IaPresents a singly ionized silicon (Si II) line at 615.0 nm (nanometers), near peak light
Type Ib/cWeak or no silicon absorption feature
Type IbShows a non-ionized helium (He I) line at 587.6 nm
Type IcWeak or no helium
Type IIShows hydrogen
Type II-P/L/NType II spectrum throughout
Type II-P/LNo narrow lines
Type II-PReaches a "plateau" in its light curve
Type II-LDisplays a "linear" decrease in its light curve (linear in magnitude versus time).[43]
Type IInSome narrow lines
Type IIbSpectrum changes to become like Type Ib
From wikipedia
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Formation of Type Ia SN
NASA, ESA and A. Feild (STScI)
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Type Ia SN as a Standard Candle
from https://www.llnl.gov/
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X-ray Bursts
• Similar to nova except that the accreting star is now neutron star: high or low mass X-ray binaries
• Observations– Repeating with irregular periods– Type I: a sharp rise followed by a slow and gradual
decline of the luminosity profile – Type II: quick pulse shape, very rarely observed
Astronomische NederlandseSatelliet
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Gamma-Ray Bursts
• Serendipitously discovered in 1960s
• Long vs Short Bursts
– Longer vs Shorter than ~2 seconds
– Soft vs Hard gamma-ray photons
– Stellar Explosion vs Merger
– Host Galaxies with High vs Low Star-Formation
• Evolution of very massive Pop III stars for long GRBs
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Neutron Stars• Observed radius and mass of NS are used to constrain the
internal structure of NS through equation of state
from the website of Dr. Matthias Hempel, http://phys-merger.physik.unibas.ch/~hempel/
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Lane-Emden Equation
Tolman–Oppenheimer–Volkoff (TOV) equation
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Introduction to FLASH
• Developed as open source at Univ. of Chicago
(Fryxell et al. 2000, ApJS)
• Modular Package written in Fortran 90
– Multi-dimension Hydrodynamics including MHD and RHD
– Parallel Adaptive Mesh Refinement by using PARAMESH
– Various physical processes: radiative cooling due to line emission,
thermal diffusion, gravity, particle tracking, ionization of atoms etc.
– Can deal with nuclear burning with selected chain reactions
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Hydrodynamicsmass, momentum and energy conservation including source terms
NewtonianSpecial Relativistic
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Nuclear Burning Module in FLASH
mass fraction
molar abundance
mass conservation
continuity equation
reaction rates
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Solve this equation by implicit method, i.e., linear solver (matrix conversion)
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Nuclear Reaction Networks
13 isotopes with
13 isotopes as above + (pp+CNO) +
19 isotope reaction network
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Example: Carbon Detonations
Timmes et al. 2000, ApJS
t=0 s
pressure
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Ran 1.5 hours with 32 processors on IBM machine to proceed to 1.6e-7 sec (1785 time steps)
Finest spatial resolution = 0.2 cm (128 cells along y-axis)
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Introduction to MESA
Modules for Experiments in Stellar Astrophysics (MESA)- developed by Paxton et al. (2011, ApJS, 192, 3)
1D stellar evolution code written in Fortran 90 Modules include
- equation of state, opacities, and thermonuclear and weakreactions
- additional nuclear reaction networks including JINA Reaclib database (more than 4500 isotopes)
- mixing length theory of convection (to complement 1D model)
- atmosphere boundary conditions- diffusion and gravitational settling
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Reaction Network
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Samples
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Proposed Activities
• Any new measurements and calculations can be used as inputs to either stellar evolution or hydrodynamics code with nuclear burning in order to be tested with observations.
• Using updated (different) reaction rates (i.e., nuclear physics) may (maybe not yet) causes a lot of differences in the results that are obtained from computer models.
• Running multi-dimensional hydrodynamic simulations with tracking a large number of isotopes.
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X-ray Bursts
Using 1300 isotopes (Kepler)Woosley et al. 2004, ApJS
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Reaction-Rate-Dependence?
JINA REACLIBCyburt et al. 2010, ApJS
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Hardware available in Korea
• Korea Astronomy and Space Science Institute (KASI)– Currently, a linux cluster with 128 CPUs– ~1000 CPU linux cluster (with GPU supports for some nodes) with
this year• Korea Institute of Science and Technology Information (KISTI)
– TACHYONⅡ (SUN B6275): 25,408 CPUs (300 TFLOPS)– TACHYON (SUN B6048): 3,008 CPUs (24 TFLOPS)– GAIA (IBM p595): 640 CPUs (5,888 GFLOPS)– GAIA (IBM p6): 1,536 CPUs (30.7TFLOPS)