English: This composite image of Cepheus B combines data from the Chandra X-ray Observatory and the Spitzer Space Telescope. A molecular cloud is a region containing cool interstellar gas and dust left over from the formation of the galaxy and mostly contains molecular hydrogen. The Spitzer data, in red, green and blue show the molecular cloud (in the bottom part of the image) plus young stars in and around Cepheus B, and the Chandra data in violet show the young stars in the field. The Chandra observations allowed the astronomers to pick out young stars within and near Cepheus B, identified by their strong X-ray emission. The Spitzer data showed whether the young stars have a so-called "protoplanetary" disk around them. Such disks only exist in very young systems where planets are still forming, so their presence is an indication of the age of a star system.