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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
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
Nuclear Physics for Astronomy
from http://www.phy.ornl.gov/hribf/science/abc/
from http://radchem.nevada.edu/
Stars
From http://www.jca.umbc.edu/~george/html/courses/
Hipparchus Observations
Image from Greg Bothun
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.
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
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
Formation of Type Ia SN
NASA, ESA and A. Feild (STScI)
Type Ia SN as a Standard Candle
from https://www.llnl.gov/
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
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
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/
Lane-Emden Equation
Tolman–Oppenheimer–Volkoff (TOV) equation
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
Hydrodynamicsmass, momentum and energy conservation including source terms
NewtonianSpecial Relativistic
Nuclear Burning Module in FLASH
mass fraction
molar abundance
mass conservation
continuity equation
reaction rates
Solve this equation by implicit method, i.e., linear solver (matrix conversion)
Nuclear Reaction Networks
13 isotopes with
13 isotopes as above + (pp+CNO) +
19 isotope reaction network
Example: Carbon Detonations
Timmes et al. 2000, ApJS
t=0 s
pressure
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)
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
Reaction Network
Samples
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.
X-ray Bursts
Using 1300 isotopes (Kepler)Woosley et al. 2004, ApJS
Reaction-Rate-Dependence?
JINA REACLIBCyburt et al. 2010, ApJS
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)
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