The Physics and Astrophysics of Type Ia Supernova Explosions

Mike Guidry

Department of Physics and AstronomyUniversity of Tennessee

Physics Division, Oak Ridge National Laboratory

Computer Science and Mathematics DivisionOak Ridge National Laboratory

Classification of Supernovae

Type Ia Supernova Observations

Tycho's Supernova

Supernova of 1006

Kepler's Supernova

Type Ia Supernova Remnants in X-rays

Type Ia Supernova 17 Mpc away in the Virgo Cluster

SNR 0509-67.5X-ray + Optical

Binary Star Systems

Chandrasekhar Limiting Mass

Degenerate Electron Gas

Behavior of Degenerate Gas

Two Competing Mechanisms

There are two primary competing mechanisms for Type Ia supernovae that have been proposed:

SINGLE DEGENERATE: In a binary system a non-degenerate star accretes onto a degenerate white dwarf.

DOUBLE DEGENERATE: Two degenerate white dwarfs in a binary merge, triggering a thermonuclear runaway.

In both cases the Type Ia explosion is produced by a thermonuclear runaway in degenerate white dwarf matter. The only issue is the nature of the triggering event.

This is of intense current observational interest. Newest data suggest that there may be more than one population, so both mechanisms may occur (possibly others too).

Single-Degenerate Mechanism

Double Degenerate (WD) Merger

W. Hillebrandt, M. Kromer, F. K. Roepke, and A. J. Ruiter, Frontiers of Physics 8, 116 (2013)

Merger of a 1 solar mass white dwarf with a 0.9 solar mass white dwarf. In the initial frame the white dwarfs are orbiting each other with a 35 s period.

At 610 s a detonation is ignited at the point marked by the +. At 612 s the detonation wave has expanded to the front marked by the black line.

Standarizable Candles

Scatter in Standardized Lightcurve

Accelerated Expansion

The Concordance Model

The Type Ia supernova data, in conjunction with anisotropies in the cosmic microwave background and normal astronomical observation of galactic clusters indicates that the mass-energy of the present Universe is approximately

70% dark energy (vacuum energy).

30% matter, of which most is dark matter.

Negligible radiation energy density (most is in the CMB).

The vacuum energy is responsible for the observed acceleration.

Understanding the Type Ia MechanismThe Type Ia precursor is ~ 1.4 solar mass thermonuclear bomb:

There are three fundamental issues for understanding the mechanism:

What triggers the explosion (merger or accretion)?

How to deal computationally with the huge range of space and time scales?

How does the thermonuclear fuel burn and what ashes does it leave behind?

Spatial-Scale Disparities

Thermonuclear Reaction Networks

Large timescale disparities

Large Networks Coupled to Hydro

The largest network coupled to hydro in the best previous simulation used 14 isotopes.

Realistically, about 400 isotopes are populated with non-zero probability.

A minimal physically-correct network coupled to the hydro requires about 150 isotopes.

Population abundance in a Type Ia simulation with a 365-isotope network

Abundance Tomography SN2002bo

Note intermediate mass elements at high velocity

Deflagration and Detonation

J. Lattimer Asto 301 notes

Deflagration to Detonation TransitionLightcurves and elemental abundances in the expanding debris, and the observed explosion energy, require a thermonuclear burn that is

Initially deflagration (subsonic flame front),

Transitioning to a detonation (supersonic flame front).

Not easy to achieve in a white dwarf environment.

Delayed Detonation Simulation

W. Hillebrandt, M. Kromer, F. K. Roepke, and A. J. Ruiter, Frontiers of Physics 8, 116 (2013)

0.93 s0.70 s 1.00 s

Delayed Detonation, Chandrasekhar Mass WD

This model was initiated by 100 ignition sparks around the center. Up until 0.93 s, the flame propagates as a deflagration (white flame front). The frame at 1 s is shortly after a detonation has been triggered (blue flame front).

Can Flames Survive Ash Obstructions?

Well-resolved detonation flames seem not able to survive ash barriers if the barrier width is a few detonation flame widths. In this 2D case the flame fails to re-form after the barrier at a computational resolution of 0.031 cm. For poorer resolution it may seem to re-form

Flame front does not re-form after barrier

Barrier opening of 20 cm

Cellular Structure in Flame Propagation

Caused by transverse instabilities in the flame propagation. The length of the cells corresponds to the burning length scale. Thus, appearance of this cellular structure indicates that the burning length has been resolved.

150-Isotope Network, Single Zone

GPU Acceleration for the Network

Stacking Multiple Networks on GPU

Thus, not only might it be possible to run one network of realistic size faster than is now possible, it may be possible to run many (say 20-30) such networks faster than it is now possible to run one such network.

Required Computational Power

Total of 299,008 CPU cores and 18,868 GPUs. Has already done 17 x 1015 floating point operations per second (17 petaflops), which is a world record. Should be capable of 27 petaflops after fully operational.

Memory: 32 GB (CPU) + 6 GB (GPU) per 18,868 nodes (710 GB total)

TitanTitan

Summary

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