High Quality Content by WIKIPEDIA articles! A protoplanetary disk (or proplyd) is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star or Herbig star. The protoplanetary disk may be considered an accretion disk because gaseous material may be falling from the inner edge of the disk onto the surface of the star, but this process should not be confused with the accretion process thought to build up the planets themselves. Protoplanetary disks around T Tauri stars differ from the discs surrounding the primary components of close binary systems in their size and temperature. Protoplanetary discs have radii up to 1000 astronomical units and are rather cool. Only their innermost parts reach temperatures above 1000 kelvin. They are very often accompanied by jets.