Issue |
A&A
Volume 457, Number 3, October III 2006
|
|
---|---|---|
Page(s) | 963 - 986 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20064855 | |
Published online | 12 September 2006 |
Multidimensional supernova simulations with approximative neutrino transport
I. Neutron star kicks and the anisotropy of neutrino-driven explosions in two spatial dimensions
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85741 Garching, Germany e-mail: scheck@mpa-garching.mpg.de
Received:
13
January
2006
Accepted:
12
June
2006
We study hydrodynamic instabilities during the first
seconds of core-collapse supernovae by means of
2D simulations with approximative
neutrino transport and boundary conditions that
parameterize the effects of the contracting neutron star
and allow us to obtain sufficiently strong neutrino heating
and, hence, neutrino-driven explosions. Confirming more
idealised studies, as well as supernova simulations with
spectral transport, we find that random seed perturbations
can grow by hydrodynamic instabilities to a globally
asymmetric mass distribution in the region between the
nascent neutron star and the accretion shock, leading to a
dominance of dipole () and quadrupole (
) modes in
the explosion ejecta, provided the onset of the supernova
explosion is sufficiently slower than the growth time scale
of the low-mode instability. By gravitational and
hydrodynamic forces, the anisotropic mass distribution
causes an acceleration of the nascent neutron star, which
lasts for several seconds and can propel the neutron star
to velocities of more than 1000 km s-1. Because
the explosion anisotropies develop chaotically and change
by small differences in the fluid flow, the magnitude of
the kick varies stochastically. No systematic dependence of
the average neutron star velocity on the explosion energy
or the properties of the considered progenitors is found.
Instead, the anisotropy of the mass ejection, and hence of the
kick, seems to increase when the nascent neutron star
contracts more quickly, and thus low-mode instabilities can
grow more rapidly. Our more than 70 models separate into
two groups, one with high and the other with low neutron
star velocities and accelerations after one second of
post-bounce evolution, depending on whether the
mode
is dominant in the ejecta or not. This leads to a
bimodality of the distribution when the neutron star
velocities are extrapolated to their terminal values.
Establishing a link to the measured distribution of pulsar
velocities, however, requires a much larger set of
calculations and ultimately 3D modelling.
Key words: hydrodynamics / instabilities / radiative transfer / neutrinos / stars: supernovae: general / pulsars: general
© ESO, 2006
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