63 research outputs found
Asymmetric core combustion in neutron stars and a potential mechanism for gamma ray bursts
We study the transition of nuclear matter to strange quark matter (SQM)
inside neutron stars (NSs). It is shown that the influence of the magnetic
field expected to be present in NS interiors has a dramatic effect on the
propagation of a laminar deflagration (widely studied so far), generating a
strong acceleration of the flame in the polar direction. This results in a
strong asymmetry in the geometry of the just formed core of hot SQM which
resembles a cylinder orientated in the direction of the magnetic poles of the
NS. This geometrical asymmetry gives rise to a bipolar emission of the thermal
neutrino-antineutrino pairs produced in the process of SQM formation. The
neutrino-antineutrino pairs annihilate into electron-positron pairs just above
the polar caps of the NS giving rise to a relativistic fireball, thus providing
a suitable form of energy transport and conversion to gamma emission that may
be associated to short gamma ray bursts (GRBs).Comment: 2 figure
Flame fronts in Supernovae Ia and their pulsational stability
The structure of the deflagration burning front in type Ia supernovae is
considered. The parameters of the flame are obtained: its normal velocity and
thickness. The results are in good agreement with the previous works of
different authors. The problem of pulsation instability of the flame, subject
to plane perturbations, is studied. First, with the artificial system with
switched-off hydrodynamics the possibility of secondary reactions to stabilize
the front is shown. Second, with account of hydrodynamics, realistic EOS and
thermal conduction we can obtain pulsations when Zeldovich number was
artificially increased. The critical Zeldovich numbers are presented. These
results show the stability of the flame in type Ia supernovae against
pulsations because its effective Zeldovich number is small.Comment: 12 pages, 11 figure
Asymmetric Explosions of Thermonuclear Supernovae
A type Ia supernova explosion starts in a white dwarf as a laminar
deflagration at the center of the star and soon several hydrodynamic
instabilities (in particular, the Rayleigh-Taylor (R-T) instability) begin to
act. In previous work (Ghezzi, de Gouveia Dal Pino, & Horvath 2001), we
addressed the propagation of an initially laminar thermonuclear flame in
presence of a magnetic field assumed to be dipolar. We were able to show that,
within the framework of a fractal model for the flame velocity, the front is
affected by the field through the quenching of the R-T instability growth in
the direction perpendicular to the field lines. As a consequence, an asymmetry
develops between the magnetic polar and the equatorial axis that gives a
prolate shape to the burning front. We have here computed numerically the total
integrated asymmetry as the flame front propagates outward through the
expanding shells of decreasing density of the magnetized white dwarf
progenitor, for several chemical compositions, and found that a total asymmetry
of about 50 % is produced between the polar and equatorial directions for
progenitors with a surface magnetic field B ~ 5 x 10^{7} G, and a composition
C12 = 0.2 and O16 = 0.8 (in this case, the R-T instability saturates at scales
\~ 20 times the width of the flame front). This asymmetry is in good agreement
with the inferred asymmetries from spectropolarimetric observations of very
young supernova remnants, which have recently revealed intrinsic linear
polarization interpreted as evidence of an asymmetric explosion in several
objects,such as SN1999by, SN1996X, and SN1997dt. Larger magnetic field
strengths will produce even larger asymmetries. We have also found that for
lighter progenitors the total asymmetry is larger.Comment: 21 pages, 8 figures, AASTEX macros, Accepted for publication in
Monthly Notices of The Royal Astronomical Societ
Flame front propagation IV: Random Noise and Pole-Dynamics in Unstable Front Propagation II
The current paper is a corrected version of our previous paper
arXiv:adap-org/9608001. Similarly to previous version we investigate the
problem of flame propagation. This problem is studied as an example of unstable
fronts that wrinkle on many scales. The analytic tool of pole expansion in the
complex plane is employed to address the interaction of the unstable growth
process with random initial conditions and perturbations. We argue that the
effect of random noise is immense and that it can never be neglected in
sufficiently large systems. We present simulations that lead to scaling laws
for the velocity and acceleration of the front as a function of the system size
and the level of noise, and analytic arguments that explain these results in
terms of the noisy pole dynamics.This version corrects some very critical
errors made in arXiv:adap-org/9608001 and makes more detailed description of
excess number of poles in system, number of poles that appear in the system in
unit of time, life time of pole. It allows us to understand more correctly
dependence of the system parameters on noise than in arXiv:adap-org/9608001Comment: 23 pages, 4 figures,revised, version accepted for publication in
journal "Combustion, Explosion and Shock Waves". arXiv admin note:
substantial text overlap with arXiv:nlin/0302021, arXiv:adap-org/9608001,
arXiv:nlin/030201
Flame front propagation I: The Geometry of Developing Flame Fronts: Analysis with Pole Decomposition
The roughening of expanding flame fronts by the accretion of cusp-like
singularities is a fascinating example of the interplay between instability,
noise and nonlinear dynamics that is reminiscent of self-fractalization in
Laplacian growth patterns. The nonlinear integro-differential equation that
describes the dynamics of expanding flame fronts is amenable to analytic
investigations using pole decomposition. This powerful technique allows the
development of a satisfactory understanding of the qualitative and some
quantitative aspects of the complex geometry that develops in expanding flame
fronts.Comment: 4 pages, 2 figure
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