Chandra X-ray Observatory Center Harvard-Smithsonian Center for Astrophysics 60 Garden St. Cambridge, MA 02138 USA http://chandra.harvard.edu

W3 Main: A region of massive star formation about 6,000 light years from Earth in the Perseus arm of the Milky Way. (Credit: X-ray: NASA/CXC/Penn State/L.Townsley et al.; Optical: Pal Obs. DSS) Caption: In this composite image of one of the many star-forming complexes of W3, the Chandra data are shown in green and blue (lower and higher-energy X-rays, respectively) and optical emission is in red. The bright, point-like X-ray sources represent an extensive population of several hundred young stars, many of which were not found in earlier studies. Because its X-ray sources are all at the same distance, yet span a range of masses, ages, and other properties, W3 is an ideal laboratory for understanding recent and ongoing star formation in one of the Milky Way's spiral arms. Scale: Image is 14 arcmin across. Chandra X-ray Observatory ACIS Image CXC operated for NASA by the Smithsonian Astrophysical Observatory