Vortices in Protoplanetary Disks

Details Vortices in Protoplanetary Disks Vortices in Protoplanetary Disks

Feb 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004kas..confe...5b&link_type=abstract

Presented at the KITP: Astrophysics Seminars, Feb 19, 2004, Kavli Institute for Theoretical Physics, University of California, S

Astronomy and Astrophysics

Astrophysics

Scientific paper

We show (via 3D spectral anelastic hydrodynamic simulations) thatfinite-amplitude perturbations in a stably stratified protoplanetarydisk lead to the natural formation of 3D, long-lived, coherent vortices.This is in contrast to previous 3D constant density studies that showedthat perturbations to Keplerian shear always rapidly decay. Our resultsare also entirely distinct from the numerous 2D studies of vortex dynamicsin the midplane of Keplerian disks: We show that vortices in the midplaneare linearly unstable with an e-folding time of only a few orbital periods;the nonlinear development of the instability leads to the destruction ofvortices in the midplane. In our numerical simulations, a midplane vortex(prior to its destruction) was a source of perturbations: as it oscillated,it excited internal gravity waves which would propagate away from the midplane,break, and create vorticity (a baroclinic effect). The regions of vorticityabove and below the midplane would coalesce into new vortices. Whereas themidplane vortex would eventually succumb to the instability, the off-midplanevortices were stable (to infinitesimal and finite-amplitude perturbations)and long-lived. The key ingredient for stable 3D vortices is stablestratification: the vertical component of protostellar gravity vanishesin the midplane, so the gas is unstratified there; off the midplane,the magnitudes of gravity and stratification increase linearly with height.Stable, 3D off-midplane vortices may play two key roles in star and planetformation: in cool, nonmagnetized disks, vortices may transport angularmomentum outward so that mass can continue to accrete onto the growingprotostar; and vortices rapidly sweep-up and concentrate dust particles,which may help in the formation of planetesimals, the basic ``building blocks''of planets, either by increasing the efficiency of binary agglomeration,or be seeding a local gravitational instability.

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