2,364 research outputs found
Combustion in thermonuclear supernova explosions
Type Ia supernovae are associated with thermonuclear explosions of white
dwarf stars. Combustion processes convert material in nuclear reactions and
release the energy required to explode the stars. At the same time, they
produce the radioactive species that power radiation and give rise to the
formation of the observables. Therefore, the physical mechanism of the
combustion processes, as reviewed here, is the key to understand these
astrophysical events. Theory establishes two distinct modes of propagation for
combustion fronts: subsonic deflagrations and supersonic detonations. Both are
assumed to play an important role in thermonuclear supernovae. The physical
nature and theoretical models of deflagrations and detonations are discussed
together with numerical implementations. A particular challenge arises due to
the wide range of spatial scales involved in these phenomena. Neither the
combustion waves nor their interaction with fluid flow and instabilities can be
directly resolved in simulations. Substantial modeling effort is required to
consistently capture such effects and the corresponding techniques are
discussed in detail. They form the basis of modern multidimensional
hydrodynamical simulations of thermonuclear supernova explosions. The problem
of deflagration-to-detonation transitions in thermonuclear supernova explosions
is briefly mentioned.Comment: Author version of chapter for 'Handbook of Supernovae,' edited by A.
Alsabti and P. Murdin, Springer. 24 pages, 4 figure
The Effects of Realistic Nuclear Kinetics, Dimensionality, and Resolution on Detonations in Low-Density Type Ia Supernovae Environments
Type Ia supernovae are most likely thermonuclear explosions of carbon/oxygen white dwarves in binary stellar systems. These events contribute to the chemical and dynamical evolution of their host galaxies and are essential to our understanding of the evolution of our universe through their use as cosmological distance indicators. Nearly all of the currently favored explosion scenarios for these supernovae involve detonations. However, modeling astrophysical detonations can be complicated by numerical effects related to grid resolution. In addition, the fidelity of the reaction network chosen to evolve the nuclear burning can alter the time and length scales over which the burning occurs. Multidimensional effects further complicate matters by introducing a complex cellular structure within the reaction zone. Here, we report on how these complications can affect the outcome of simulating such astrophysical detonations in the context of Type Ia supernovae
Small-scale Interaction of Turbulence with Thermonuclear Flames in Type Ia Supernovae
Microscopic turbulence-flame interactions of thermonuclear fusion flames
occuring in Type Ia Supernovae were studied by means of incompressible direct
numerical simulations with a highly simplified flame description. The flame is
treated as a single diffusive scalar field with a nonlinear source term. It is
characterized by its Prandtl number, Pr << 1, and laminar flame speed, S_L. We
find that if S_L ~ u', where u' is the rms amplitude of turbulent velocity
fluctuations, the local flame propagation speed does not significantly deviate
from S_L even in the presence of velocity fluctuations on scales below the
laminar flame thickness. This result is interpreted in the context of
subgrid-scale modeling of supernova explosions and the mechanism for
deflagration-detonation-transitions.Comment: 8 pages, 6 figures, accepted by Astrophys.
Type Ia Supernova Explosion Models: Homogeneity versus Diversity
Type Ia supernovae (SN Ia) are generally believed to be the result of the
thermonuclear disruption of Chandrasekhar-mass carbon-oxygen white dwarfs,
mainly because such thermonuclear explosions can account for the right amount
of Ni-56, which is needed to explain the light curves and the late-time
spectra, and the abundances of intermediate-mass nuclei which dominate the
spectra near maximum light. Because of their enormous brightness and apparent
homogeneity SN Ia have become an important tool to measure cosmological
parameters. In this article the present understanding of the physics of
thermonuclear explosions is reviewed. In particular, we focus our attention on
subsonic (``deflagration'') fronts, i.e. we investigate fronts propagating by
heat diffusion and convection rather than by compression. Models based upon
this mode of nuclear burning have been applied very successfully to the SN Ia
problem, and are able to reproduce many of their observed features remarkably
well. However, the models also indicate that SN Ia may differ considerably from
each other, which is of importance if they are to be used as standard candles.Comment: 11 pages, 4 figures. To appear in Proc. 10th Ann. Astrophys. Conf.
"Cosmic Explosions", Univ. of Maryland 1999, eds. S.S. Holt and W.W. Zhan
Multi-dimensional numerical simulations of type Ia supernova explosions
The major role type Ia supernovae play in many fields of astrophysics and in
particular in cosmological distance determinations calls for self-consistent
models of these events. Since their mechanism is believed to crucially depend
on phenomena that are inherently three-dimensional, self-consistent numerical
models of type Ia supernovae must be multi-dimensional. This field has recently
seen a rapid development, which is reviewed in this article. The different
modeling approaches are discussed and as an illustration a particular explosion
model -- the deflagration model -- in a specific numerical implementation is
presented in greater detail. On this exemplary case, the procedure of
validating the model on the basis of comparison with observations is discussed
as well as its application to study questions arising from type Ia supernova
cosmology.Comment: 30 pages, 7 figures (Fig. 6 with reduced resolution
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