Evaporating Planetary Disks
Thursday, February 9, 2012
Science Update - A look at CfA discoveries from recent journals

A protoplanetary disk is a rotating disk of gas and dust around a newborn star. Astronomers think that after a few million years, planets will develop out of such protoplanetary disks when the conditions are suitable. If, however, the star happens to have formed in the presence of other young stars, in particular ones that are massive, then the powerful ultraviolet radiation from those massive stars can evaporate some or all of the material in the protoplanetary disk.

A "proplyd" is the name given to a protoplanetary disk that has been partly eroded by external ultraviolet radiation, typically into tadpole-like shapes that point towards the source of UV. The first proplyds were discovered in the nearby Orion molecular cloud, where they are bathed in the corrosive illumination of the four famous hot, young stars in the Trapezium cluster. Astronomers trying to understand how stars and planets form and evolve have been looking for proplyds in other places to test their theories, since most newly formed stars have hot neighbors nearby that could inhibit the maturation of their planetary systems.

CfA astronomers Nick Wright, Jeremy Drake, Mario Guarcello, and Joe Hora, together with three colleagues, report discovering a family of ten proplyd-like objects located only about 30 light-years away from the giant supercluster (about sixty-five massive, hot stars) in the Cygnus OB2 association. The Cygnus cluster is farther away from us than the Orion region, and a much more extreme case of a hot young cluster. The scientists report finding that the Cygnus objects have morphological differences in size and shape that could indicate they are not true proplyds (disks) but rather evaporating gas globules (perhaps failed stars), or even a new class of photo-evaporated, embedded young stars that have managed to survive the UV destructing of their natal clouds. The research, which is continuing with additional studies of spectral and energy analyses, marks a important step forward in understanding how planetary disks evolve under harsh conditions.