Massive stars forming in nebula DR21, Spitzer Space Telescope image. DR21 is a region (centre, top) about 10,000 light years away in the constellation Cygnus. It is a bright source of radio emission, but heavy dust obscures all its light. Infrared cameras on Spitzer penetrate this, revealing a stellar nursery for stars up to 100,000 times as bright as the sun. There is a gaseous outflow from DR21 (green). The red filaments in the image glow because of polycyclic aromatic hydrocarbons (PAHs), which are excited into luminescence by radiation at wavelengths near 8 microns. Blue represents wavelengths of 3.6 microns, rising through green and orange to red at 8 microns.