NGC7538

NGC 7538 is a star cluster surrounded by an emission nebula. The distance to it is about 7900 light years. The nebula consists mainly of hydrogen gas, but also contains cosmic dust, which glows brightly in the far infrared spectrum. With a total mass of about 400,000 times the mass of our Sun, the nebula is an active star factory, especially for large stars with a mass of more than eight solar masses. Hundreds of protostars are scattered throughout the nebula. Once they reach a critical mass, nuclear fusion begins, and they begin to glow as stars. Thirty of these protostars have a mass of more than 40 solar masses and are very cold — only a few tens of kelvins.