... Spiral disks are loose conglomerations of billions of stars and diffuse gas all gravitationally orbiting a galaxy center. Burning Tree Sprite . ... Known as R136, the cluster's energetic stars are breaking out of the cocoon of gas and dust from which they formed. ... This planetary nebula's simple, graceful appearance is thought to be due to perspective -- our view from planet Earth looking straight into what is actually a barrel-shaped cloud of gas shrugged off by a dying central star. ...