233 research outputs found
On the Formation of Gas Giant Planets on Wide Orbits
A new suite of three dimensional radiative, gravitational hydrodynamical
models is used to show that gas giant planets are unlikely to form by the disk
instability mechanism at distances of ~100 AU to ~200 AU from young stars. A
similar result seems to hold for the core accretion mechanism. These results
appear to be consistent with the paucity of detections of gas giant planets on
wide orbits by infrared imaging surveys, and also imply that if the object
orbiting GQ Lupus is a gas giant planet, it most likely did not form at a
separation of ~100 AU. Instead, a wide planet around GQ Lup must have undergone
a close encounter with a third body that tossed the planet outward to its
present distance from its protostar. If it exists, the third body may be
detectable by NASA's Space Interferometry Mission.Comment: 13 pages, 4 figures. in press, ApJ Letter
Three-dimensional evolution of early solar nebula
The progress is reported toward the goal of a complete theory of solar nebula formation, with an emphasis on three spatial dimension models of solar nebular formation and evolution. The following subject areas are covered: (1) initial conditions for protostellar collapse; (2) single versus binary star formation; (3) angular momentum transport mechanisms; (4) three dimensional solar nebula models; and (5) implications for planetary formation
Collapse and Fragmentation of Molecular Cloud Cores. X. Magnetic Braking of Prolate and Oblate Cores
The collapse and fragmentation of initially prolate and oblate, magnetic
molecular clouds is calculated in three dimensions with a gravitational,
radiative hydrodynamics code. The code includes magnetic field effects in an
approximate manner: magnetic pressure, tension, braking, and ambipolar
diffusion are all modelled. The parameters varied for both the initially
prolate and oblate clouds are the initial degree of central concentration of
the radial density profile, the initial angular velocity, and the efficiency of
magnetic braking (represented by a factor or ). The
oblate cores all collapse to form rings that might be susceptible to
fragmentation into multiple systems. The outcome of the collapse of the prolate
cores depends strongly on the initial density profile. Prolate cores with
central densities 20 times higher than their boundary densities collapse and
fragment into binary or quadruple systems, whereas cores with central densities
100 times higher collapse to form single protostars embedded in bars. The
inclusion of magnetic braking is able to stifle protostellar fragmentation in
the latter set of models, as when identical models were calculated without
magnetic braking (Boss 2002), those cores fragmented into binary protostars.
These models demonstrate the importance of including magnetic fields in studies
of protostellar collapse and fragmentation, and suggest that even when magnetic
fields are included, fragmentation into binary and multiple systems remains as
a possible outcome of protostellar collapse.Comment: 20 pages, 8 figures. Astrophysical Journal, in pres
On Pressure Gradients and Rapid Migration of Solids in an Inhomogeneous Solar Nebula
We study the motions of small solids, ranging from micron-sized dust grains
to 100-m objects, in the vicinity of a local density enhancement of an
isothermal gaseous solar nebula. Being interested in possible application of
the results to the formation of clumps and spiral arms in a circumstellar disk,
we numerically integrate the equations of motion of such solids and study their
migration for different values of their sizes and masses and also for different
physical properties of the gas, such as its density and temperature. We show
that, considering the drag force of the gas and also the gravitational
attraction of the nebula, it is possible for solids, within a certain range of
size and mass, to migrate rapidly (i.e. within ~1000 years) toward the location
of a local maximum density where collisions and coagulation may result in an
accelerated rate of planetesimal formation.Comment: 20 pages, 7 figures, submitted for publicatio
- …