Radiation Hydrodynamics Simulations of Spherical Protostellar Collapse for Very Low Mass Objects. (arXiv:1811.04593v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Stamer_T/0/1/0/all/0/1">Torsten Stamer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Inutsuka_S/0/1/0/all/0/1">Shu-ichiro Inutsuka</a>
We perform radiation hydrodynamical simulations of protostellar collapse in
spherical symmetry, with a special focus on very low-mass objects, i.e. brown
dwarfs and sub-brown dwarfs. The inclusion of a realistic equation of state
that includes the effect of hydrogen dissociation allows for a modeling of the
complete process from the beginning of the collapse until the formation of the
protostar. We solve the frequency-dependent radiative transfer equation without
any diffusion approximation, using realistic dust and gas opacities.
Our results show that the properties of the protostar are essentially
independent of the initial conditions, which had previously only been confirmed
for higher mass ranges. For very low mass initial conditions, however, we find
that the first core phase of the collapse shows some significant differences in
the time evolution, with the first core lifetime increasing dramatically
because of the reduced accretion rate from the surrounding envelope. We
consider the observational implications of this. We also investigate the
opposite case of a collapse without any first core phase, which may occur for
very unstable initial conditions.
In the appendix, we describe a severe numerical problem that causes an
unphysical expansion after the formation of the protostar, which may affect
other attempts at similar calculations of self-gravitational collapse. We
explain the origin of the unphysical behavior and present a solution that can
be used in similar investigations.
We perform radiation hydrodynamical simulations of protostellar collapse in
spherical symmetry, with a special focus on very low-mass objects, i.e. brown
dwarfs and sub-brown dwarfs. The inclusion of a realistic equation of state
that includes the effect of hydrogen dissociation allows for a modeling of the
complete process from the beginning of the collapse until the formation of the
protostar. We solve the frequency-dependent radiative transfer equation without
any diffusion approximation, using realistic dust and gas opacities.
Our results show that the properties of the protostar are essentially
independent of the initial conditions, which had previously only been confirmed
for higher mass ranges. For very low mass initial conditions, however, we find
that the first core phase of the collapse shows some significant differences in
the time evolution, with the first core lifetime increasing dramatically
because of the reduced accretion rate from the surrounding envelope. We
consider the observational implications of this. We also investigate the
opposite case of a collapse without any first core phase, which may occur for
very unstable initial conditions.
In the appendix, we describe a severe numerical problem that causes an
unphysical expansion after the formation of the protostar, which may affect
other attempts at similar calculations of self-gravitational collapse. We
explain the origin of the unphysical behavior and present a solution that can
be used in similar investigations.
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