Statistics – Computation
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt.........7b&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF TEXAS AT AUSTIN, 1996.Source: Dissertation Abstracts International, Volume: 57-06, Section: B,
Statistics
Computation
1
White Dwarf
Scientific paper
The thermonuclear explosion of a carbon-oxygen white dwarf that has accreted mass until it approaches the Chandrasekhar limit is widely accepted to be the correct model for Type Ia supernovae (SN Ia). The basic observational characteristics of these models are in general agreement with the observed composition, light curves, and velocities of the ejecta. The mechanism for the explosion, however, is still under debate. Some deflagration models give better agreement with observations, but physical arguments imply that the ignition of a detonation may be unavoidable. Recent numerical models invoking both mechanisms (delayed, or pulsed, detonation models) have yielded promising results. It seems likely that a detonation is at least part of the explosion process for SN Ia. Therefore, understanding detonation propagation in degenerate carbon-oxygen matter is essential. We have constructed a two-dimensional hydrocode with nuclear energy release to study this problem by investigating the multidimensional structure of detonations. Experimental and computational results for detonations in terrestrial fuel-air mixtures show that multidimensional effects are critical to understanding the propagation of real detonations. Multidimensional effects can lead to slower and/or unsteady detonation propagation in simulations of fuel-air mixtures, providing much better agreement with experiments than 1D calculations. We present the first results to show that multidimensional effects are also important for detonations in degenerate carbon -oxygen matter. Perturbations induce transverse waves in the carbon-burning layer, which interact and create pockets of unburned material. This increases the effective size of the induction zone relative to 1D calculations and weakens the detonation. Therefore, the detonation is expected to die at a higher density than predicted by 1D calculations. The presence of these pockets of unburned material also produces a different composition distribution than is produced by 1D models; pockets of unburned material exist far behind the shock front, in contradiction to 1D calculations. In addition, multidimensional effects might be the key to explaining the nature of the recently-discovered inhomogeneities in SN Ia. This would give greater insight into the use of SN Ia as distance indicators for determining the intergalactic distance scale and the Hubble constant.
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