2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009;
Denver, Colorado
Session Q5: Computational Astrophysics of Disks: From Black Holes to Planets
10:45 AM–12:33 PM,
Monday, May 4, 2009
Room: Governor's Square 15
Sponsoring
Unit:
DCOMP
Chair: Richard Klein, Lawrence Livermore National Laboratory
Abstract ID: BAPS.2009.APR.Q5.2
Abstract: Q5.00002 : Radiative Hydrodynamics and the Formation of Gas Giant Planets
11:21 AM–11:57 AM
Preview Abstract
Abstract
Author:
Richard H. Durisen
(Indiana University)
Gas giant planets undoubtedly form from the orbiting gas and dust
disks commonly observed around young stars, and there are two
principal mechanisms proposed for how this may occur. The core
accretion plus gas capture model argues that a solid core forms
first and
then accretes gas from the surrounding disk once the core becomes
massive
enough (about 10 Earth masses). The gas accumulation process is
comparatively slow but becomes hydrodynamic at later times. The disk
instability model alternatively suggests that gas giant planet
formation
is initiated by gas-phase gravitational instabilities (GIs) that
fragment
protoplanetary disks into bound gaseous protoplanets rapidly, on disk
orbit period time scales. Solid cores then form more slowly by
accretion
of solid planetesimals and settling. The overall formation time
scales for
these two mechanisms can differ by orders of magnitude. Both
involve multidimensional hydrodynamic flows at some phase, late
in the
process for core accretion and early on for disk instability. The
ability
of cores to accrete gas and the ability of GIs to produce bound
clumps
depend on how rapidly gas can lose energy by radiation. This
regulatory
process, while important for controlling the time scale for core
accretion
plus gas capture, turns out to be absolutely critical for disk
instability
to work at all. For this reason, I will focus in my talk on the
use of
radiation hydrodynamics simulations to determine whether and where
disk instability can actually form gas giant planets in disks.
Results
remain controversial, but simulations by several different research
groups support analytic arguments that disk instability leading to
fragmentation probably cannot occur in disks around Sun-like stars at
orbit radii of 10's of Earth-Sun distances or less. On the other
hand, very
recent simulations suggest that very young, rapidly accreting
disks with
much larger radii (100's of times the Sun-Earth distance) can indeed
readily fragment by disk instability into super-Jupiters and
brown dwarfs.
It is possible that there are two distinct modes of gas giant planet
formation in Nature which operate at different times and in different
regions of disks around young stars. The application of more
radiative
hydrodynamics codes with better numerical techniques could play an
important role in future theoretical developments.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.APR.Q5.2