Feb 15, 2017
Picture of the month
This composite multi-wavelength image invokes thoughts of a frosty winter landscape. In reality, it is a rather hot place in our Galaxy about 5500 light-years from Earth in the constellation Scorpius. The region called NGC 6357 is an association of at least three clusters of young stars, including many hot, massive luminous stars. The purple-coded X-ray emission is based on observations from the Chandra X-ray Observatory and from the earlier ROSAT satellite, and reveals hundreds of point sources, which are young stars, as well as diffuse emission from hot interstellar gas bubbles. The orange-coded infrared observations from NASA’s Spitzer Space Telescope trace dusty filaments of cold gas surrounding these cavities, while blue is used for the optical emission observed by the UK Infrared Telescope. Such star-forming clouds are called “HII” (pronounced “H-two”) regions, because the intense UV emission of the newborn stars photo-ionises the hydrogen gas.
About the author
Compiled by Marc Türler, ISDC and Observatory of the University of Geneva, and CHIPP, University of Zurich.