Three Dimensional Simulations Of The Deflagration Phase of the Gravitationally Confined Detonation Model of Type Ia Su

1. Three Dimensional Simulations Of The Deflagration Phase of the Gravitationally Confined Detonation Model of Type Ia Supernovae Presented By: Paul Grenning

2. Deflagration and Detonation • Deflagration is the ignition and combustion • Gasoline deflagrates when lit with a match • Detonation is the explosive force or shock compression • Dynamite detonates

3. What are type Ia Supernovae • Created by White Dwarf Stars • Final stage in a stars life • Super dense stars with the approximate energy of our sun but the size of our earth. • The White Dwarf reaches the ignition temperature for carbon fusion • White Dwarf merges with a second star it will exceed the temperature required for nuclear fusion and release enough energy to create the Ia Supernova • Releases as much energy as our sun emits over its entire life span

4. Authors/Contributors • Cal Jordan • Robert Fisher • D. M. Townsley • A. C. Calder • C. Graziani • S. Asida • D. Q. Lamb • J. W. Truran

5. Robert Fisher • The primary theme of my research is the fundamental physics of turbulent flows, and its application to a variety of astrophysical phenomena. • Interstellar Medium and Star Formation • Computational Physics • Works at Dartmouth college in MA in the department of physics

6. Dean Townsley • My research interests lie in refining stellar physics via its application to novel and dynamic astrophysical systems • Visiting professor at University Of Chicago • Assistant Professor at the University Of Alabama in the Department of Physics and Astronomy

7. Project Background • Their work is being done at the University of Chicago's Center for Astrophysical Thermonuclear Flashes • The scientists and engineers are using Argonne’s super computer Blue Gene/P to create the simulations • GCD (Gravitationally Confined Detonation)

8. Project Goal • To show the detonation conditions in a three dimensional simulation in the GCD model is possible • In the past, extensive two-dimensional cylindrical simulations have shown that detonation conditions are robustly reached in the GCD model for a variety of initial conditions • They believe that the conditions to create this type of supernova can be better viewed in 3D rather than 2D

9. Why Is This Important? • Type Ia Supernovae are “Standard Candles” • These types of supernovae have revealed that the rate at which the universe is expanding is accelerating • This has led to the discovery of “dark energy” • The biggest concern is that we do not know the causes of these supernovae • Current models include • Pure Deflagration (PD) • Deflagration To Detonation Transition (DDT) • Pulsational Detonation (PD) • Gravitationally Confined Detonation (GCD) • Only one to show the detonation arise naturally

10. Simulation Setup • Simulations use FLASH 3.0 • An adaptive mesh hydrodynamics code for modeling astrophysical thermonuclear flashes (such as Supernovae, X-Ray Bursts, and classical Novae) • Uses the (advection-diffusion-reaction)ADR flame model • Numerically quieter • More stable • Exhibits smaller curvature effects • Leaves out nuclear burning outside the flame because with it there would be too much overhead to show such a robust simulation

11. Initial Conditions • Size of the flame bubble or thermonuclear flame containing iron and other elements • Amount of iron and other elements • Resolution • Offset of the flame bubble from the center

12. Calculations • Calculations based on fluid dynamics • Use the Rayleigh-Taylor instability model • Instability of and interface between two fluids of different densities which occurs when the lighter fluid pushes the heavier fluid • Often creates a mushroom shape as the fluids merge and pass through each other and become R-T unstable

13. Simulation Details • Initially stationary thermonuclear flame at some measured offset from the center • The flame produces hot ash • Velocity increases due to buoyancy and a mushroom like bubble appears. • Velocity is much slower at the center due to the intense gravitational pull • Velocity continues to increase as it moves to the surface of the star and spreads rapidly over the surface. • Prior to hitting the surface, the bubble is carrying a range of densities of iron and other elements • The ash breaks out of but remains gravitationally bound to the surface of the star • Collides at a point on the opposite side of the star from the breakout location and incinerates the star

14. Videos • http://www.youtube.com/watch?v=5tjd9KAPais • The blue shows the approximate surface of the star and the orange shows the interface between the star and the hot ash produced by the flame. • http://www.youtube.com/watch?v=DBNy4WVm3D4 • In the animation, green represents the approximate surface of the star and the colors mark regions of high temperature in the billions of degrees Kelvin.

15. Results • They ran 7 simulations for this paper • Different starting parameters • Conservative conditions necessary for detonation are achieved in all cases • Ran more simulations with higher resolution and farther offsets from the center and received similar results

16. Detonation 2D versus 3D • Computationally the results were similar with their previous 2D simulation.

17. Results • The result is based on their conclusion that buoyancy driven nuclear burning is dependent on fluid dynamics on large scales. • It is the kinetic energy originating from the breakout of the bubble of hot ash imparted to the unburnt surface layers of the star by the inwardly moving jet generated by collision of the surface flows, that causes the unburnt material to achieve the conditions for detonation

18. Results Continued • Explosions produced large amounts of Nickel and small amounts of other elements • Different mass stars could explain the high levels of Nickel • The conditions are only for high-luminosity Type Ia supernovae

19. Future Work • Multiple ignitions near the center of the star • Produces a lower luminous explosion

20. References • Jordan, Cal., Fisher, Robert., and Townsley, Dean, et al. “Three Dimensional Simulations Of The Deflagration Phase of the Gravitationally Confined Detonation Model of Type Ia Supernovae.” The Astrophysical Journal. 681.2, (July 2008): 1448-1457 • Fryxell, B., Olson, K., and Ricker, P., et al. “FLASH: An Adaptive Mesh Hydrodynamics Code for Modeling Astrophysical Thermonuclear Flashes.” The Astrophysical Journal Supplement Series. 131.1, (November, 2000): 273-334 • http://en.wikipedia.org/wiki/Type_Ia_supernova