disks

Protoplanetary disks are rotating disks of gas and dust that surround young stars. They are believed to be the birthplace of planets, and are composed of the material left over from the star's formation. The material in these disks is thought to eventually form into planets, asteroids, comets, and other bodies. Protoplanetary disks can be observed with telescopes such as the Hubble Space Telescope and ALMA (Atacama Large Millimeter/submillimeter Array).

disks.

\acknowledgements
We thank the referee, Dr.~David Wilner, for his helpful comments.
This work was supported by the National Science Foundation under
grant AST-9988230 to the University of Florida. The authors also
acknowledge support from NASA Origins of Solar Systems program grant
NAG5-10779 and from NSF grant AST-0086246 to the University of Texas at
Austin. This research has made use of NASA's Astrophysics Data System
Abstract Service and the SIMBAD database, operated at CDS, Strasbourg,
France.


















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A protoplanetary disk is a rotating circumstellar disk of gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, because gases or other material may be falling from the inner edge of the disk onto the surface of the star. This process should not be confused with the accretion process thought to build up the planets themselves. Externally illuminated photo-evaporating protoplanetary disks are called proplyds.