409 research outputs found
Dynamics of Protoplanetary Disks
Protoplanetary disks are quasi-steady structures whose evolution and
dispersal determine the environment for planet formation. I review the theory
of protoplanetary disk evolution and its connection to observations.
Substantial progress has been made in elucidating the physics of potential
angular momentum transport processes - including self-gravity,
magnetorotational instability, baroclinic instabilities, and magnetic braking -
and in developing testable models for disk dispersal via photoevaporation. The
relative importance of these processes depends upon the initial mass, size and
magnetization of the disk, and subsequently on its opacity, ionization state,
and external irradiation. Disk dynamics is therefore coupled to star formation,
pre-main-sequence stellar evolution, and dust coagulation during the early
stages of planet formation, and may vary dramatically from star to star. The
importance of validating theoretical models is emphasized, with the key
observations being those that probe disk structure on the scales, between 1 AU
and 10 AU, where theory is most uncertain.Comment: Annual Review of Astronomy and Astrophysics (2011). Final edited
version at
http://www.annualreviews.org/doi/abs/10.1146/annurev-astro-081710-102521
.High resolution versions of illustrations at
http://jila.colorado.edu/~pja/araa.htm
On the formation time scale and core masses of gas giant planets
Numerical simulations show that the migration of growing planetary cores may
be dominated by turbulent fluctuations in the protoplanetary disk, rather than
by any mean property of the flow. We quantify the impact of this stochastic
core migration on the formation time scale and core mass of giant planets at
the onset of runaway gas accretion. For standard Solar Nebula conditions, the
formation of Jupiter can be accelerated by almost an order of magnitude if the
growing core executes a random walk with an amplitude of a few tenths of an au.
A modestly reduced surface density of planetesimals allows Jupiter to form
within 10 Myr, with an initial core mass below 10 Earth masses, in better
agreement with observational constraints. For extrasolar planetary systems, the
results suggest that core accretion could form massive planets in disks with
lower metallicities, and shorter lifetimes, than the Solar Nebula.Comment: ApJL, in pres
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