1. An Accelerated Strategic Computing Initiative (ASCI) Academic Strategic Alliances Program (ASAP) Center at The University of Chicago The Center for Astrophysical Thermonuclear Flashes Adaptive Mesh Simulations of Astrophysical Detonations Using the ASCI Flash Code Bruce Fryxell University of Chicago ACAT 2000 Fermilab - Oct. 16, 2000

2. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Astrophysical Detonations Collaborators : Alan CalderPaul Ricker Jonathan DursiBob Rosner Don LambFrank Timmes Peter MacNeiceHenry Tufo Kevin OlsonMike Zingale

3. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Overview I.The Flash problem II.Description of the Flash code III.Helium detonations on neutron stars (X-ray bursts) IV.Carbon detonations in white dwarfs (Type Ia supernovae)

4. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago What Is the FLASH Problem? To simulate the accumulation matter onto the surface of compact stars, nuclear ignition of the accreted (and possibly underlying stellar) material, and the subsequent evolution of the star’s interior, surface, and exterior X-ray bursts (on neutron star surfaces) Novae (on white dwarf surfaces) Type Ia supernovae (in white dwarf interiors) Credit: NASA/HST artist

5. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago The Astrophysical Problem Type Ia Supernova (White Dwarf) X-ray Burst (Neutron Star) Nova (White Dwarf) White dwarf: R ~ R Earth Neutron star: R ~ R Chicago

6. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Description of FLASH Code Fully compressible hydrodynamics Piecewise-Parabolic Method (Colella & Woodward) Adaptive mesh refinement Block-structured AMR (PARAMESH) One, two or three spatial dimensions Cartesian, cylindrical, or spherical Equation of state for degenerate matter Reaction networks for nuclear burning Thermal conduction Poisson Solver for self gravity

7. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Description of FLASH Code Portable ASCI Red, ASCI Blue Pacific, Nirvana Cray T3E Beowulf clusters Workstations Fully parallel MPI, HDF 5 Scales to 1024+ processors 0.25 TFLOPS on 6000 processors of ASCI Red 2000 Gordon Bell finalist Object-oriented framework

8. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago X-ray Burst Simulation Accretion of hydrogen-rich material onto the surface of a neutron star When the hydrogen reaches the surface, it burns “quietly” to helium forming a narrow layer After the helium reaches a sufficient depth (about 100 m), it becomes unstable A thermonuclear runaway initiates at a point at the base of the helium layer A burning front (detonation or deflagration) propagates across the surface of the neutron star, burning the entire layer to iron

9. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Initial Model Parameters Initial neutron star initial model generated from one-dimensional stellar evolution calculation R = 14 km, M = 1.4 M  g = 9.48 x 10 13 cm s -2 Accretion rate = 2 x 10 -11 M  / yr Conditions in helium layer at time of runaway h = 110 m M = 1.22 x 10 25 g  base = 4 x 10 8 g cm -3 T base = 1 x 10 8 o K Computational grid Two-dimensional cylindrical coordinates (axi-symmetric) 2 km wide x 1.5 km high Minimum zone size = 1 m x 1 m Effective resolution 2000 x 1500

10. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago X-ray Burst Simulation

11. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago X-ray Burst Simulation

12. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago X-ray Burst Simulation

13. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Density Evolution

14. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Adaptive Mesh Behavior

15. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Carbon Detonations in White Dwarfs Want to study the small-scale structure which develops behind the detonation front in a Type Ia supernova explosion An initial planar detonation is subject to a multi- dimensional instability which produces a cellular structure behind the front, resulting in pockets of unburned material Initial model chosen to represent the conditions in the interior of a white dwarf: C 12 at a density of 4 x 10 8 g cm -3 Three-dimensional Cartesian grid Domain size – 12.8 x 12.8 x 256 cm Grid size (if fully refined) – 256 x 256 x 5120

16. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Carbon Detonations in White Dwarfs Pressure Evolution

17. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Carbon Detonations in White Dwarfs Pressure Evolution

18. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Carbon Detonations in White Dwarfs PressureMax Pressure Si 28 Ashes

19. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Carbon Detonations in White Dwarfs Cross-section of Pressure

20. The ASCI/Alliances Center for Astrophysical Thermonuclear Flashes The University of Chicago Carbon Detonations in White Dwarfs Volume Rendered Image of Pressure