HPC in Physics (particularly astrophysics) Reuben D. Budiardja Scientific Computing National Institute for Computational Sciences 1
Gravitational Wave Einstein s Unfinished Symphony Marcia Bartuciak Predicted by Einstein s General Relativity (1915) GR gravity is the effect of space-time curvature due to mass, not mysterious action-at-a-distance 2
Gravitational Wave Einstein s Unfinished Symphony Marcia Bartuciak Predicted by Einstein s General Relativity (1915) GR gravity is the effect of space-time curvature due to mass, not mysterious action-at-a-distance Accelerating massive object produces ripples of space-time curvature gravitational waves 3
Gravitational Wave Einstein s Unfinished Symphony Marcia Bartuciak GW has not been directly detected, but new detectors are (coming) online: (A)LIGO, VIRGO, GEO600 GW astronomy will be a novel way to see nature, complementing EW (visible lights, infrared, xray, ) 4
Sources of Gravitational Wave Gravitational wave templates (frequency, spectrum) from HPC simulations are required to extract signals from background noise. 5
Binary Neutron Star Mergers Neutron star: dense object left behind by core-collapse supernovae Discovered as solitary object (pulsars) and in binary system Binary NS inspiral due to gravitational wave emissions Candidate for GRB progenitors, GW detection, r-process nucleosynthesis 6
Modeling BNS in HPC Fluid evolution Magnetic fields in fluid Nuclear Physics for equation of state Self-gravity (Newtonian + GR correction) or Full GR Radiation (Neutrino) transport Multi-dimensional simulations Inherently 3D phenomena Multi-scale Different length-scales need to be resolved: star surface, orbital, outer boundaries Adaptive Mesh Refinement (AMR) to save computational cost 7
General Astrophysics Simulation System (GenASiS) Code base for large-scale astrophysics simulations Initial target applications: Neutron star mergers, core-collapse supernovae Written entirely in Modern Fortran (2003, 2008) Modular, Object-oriented design, Extensible Eulerian/grid-base, multi-dimensional Multi-physics solver (magnetohydrodynamics, gravity, EoS, ) AMR capability
Domain Decomposition Parallelization GenASiS uses brick decomposition to minimize surface-to-volume ratio 9
Test Driven Development 10
Weak Scaling How the solution time varies with increasing number of processors given a fixed problem size per process add more processors to solve bigger problem 11
NS Merger Simulation Hydrostatic polytrope as simplified model for a neutron star Each star is given initial velocity for circular Keplerian orbit Gravitational radiation removes energy causing inspiraling 12
NS Merger Simulation Visualization movie may be viewed at: http://youtu.be/luvprmdvduw 13
Gravitational Wave merger App. Point Mass inspiral ring down 14
Core-Collapse Supernovae The death throes of massive star ( M > ~10 Solar M) Among the most powerful explosions in the universe: Occur about twice per century in our galaxy Dominant source of elements in the universe Answers to questions relating to our origins in the universe 15
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Stationary Accretion Shock Instability (SASI) Stalled shock-wave after core bounces Unstable to non-radial perturbation SASI SASI have been observed in many supernova simulations The key ingredient to robust supernova explosion? 17
Magnetic Fields in Supernovae Weak magnetic fields in progenitors Amplification usually relies on fast rotation Pulsars have strong magnetic fields Most progenitors are only slowly rotating The role of magnetic fields in supernova dynamics is not clear 18
Can SASI amplify the magnetic fields of the progenitor star? Yes, magnetic fields are amplified exponentially 19
Simulation Movie Visualization movie may be viewed at: http://youtu.be/gmfwmiylezu 20
Magnetic Fields Slice on XZ-Plane Plane s normal is Parallel to angular momentum of the flow 21
Amplification Mechanism Stretching is the primary mechanism for amplification of magnetic energy at the expense of the kinetic energy. Amplification stops due to finite resolution that cannot resolve thinner flux rope. 2X Resolution 22
Magnetic Field in Proto Neutron Star Visualization movie may be viewed at: http://vimeo.com/27247968 23