... Landsat 7 Views Planet Earth . ... Spiral disks are loose conglomerations of billions of stars and diffuse gas all gravitationally orbiting a galaxy center. ... Where did all the stars go? ... Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. Polar Ring Galaxy NGC 4650A . ... A rare type of galaxy known as a Polar Ring, NGC 4650A is composed of an old central group of stars and a young ring of stars rotating farther out. ...