W51 High-Mass Star Forming Region

The above image, taken at thermal infrared wavelengths (at 3 microns) probes the birth-place of high-mass stars. The young stars, born from massive molecular clouds, emit strongly at UV wavelengths. These high-energy photons are trapped inside the cloud; they heat and ionise the surrounding natal cloud which then emits intense infrared radiation. The "bubbles" of ionised gas are called HII regions.

In this particular region, known as W51, the bottom lobe appears to be associated with a single, shell-like HII region, while the top lobe is resolved into several compact sources, some of which are probably "ultracompact" HII regions. These compact objects are associated with the very youngest stages of high-mass stellar birth. The region also harbours a system of masers and a strong millimeter source; all are signs of the presence of massive, young protostars.

Our thanks to Sebastiano Ligori of the Max-Plank-Institute for Astronomy in Heidelberg, Germany, for allowing us to reproduce these data prior to publication. The data were reduced with the ORAC data acquisition and reduction software now available at UKIRT to all astronomers.