A proplyd, short for ionized protoplanetary disk, is an externally illuminated photoevaporating protoplanetary disk around a young star. Nearly 180 proplyds have been discovered in the Orion Nebula. Images of proplyds in other star-forming regions are rare, while Orion is the only region with a large known sample due to its relative proximity to Earth.
Proplyds in the Orion Nebula
Illustration of the dynamics of a proplyd, including an astrophysical jet
Dusty proplyds pointing to HD 17505 in Westerhout 5 as seen by the Spitzer Space Telescope
View of several proplyds within the Orion Nebula taken by the Hubble Space Telescope
Photoevaporation is the process where energetic radiation ionises gas and causes it to disperse away from the ionising source. The term is typically used in an astrophysical context where ultraviolet radiation from hot stars acts on clouds of material such as molecular clouds, protoplanetary disks, or planetary atmospheres.
Eagle nebula pillars being photoevaporated
Photoevaporation occurring to a protoplanetary disk due to the presence of a nearby O-type star