Figure 11-14An H II Region This emission nebula, M16, called the Eagle Nebula because of its shape, surrounds a star cluster. It is so numbered because it was the sixteenth object in the Messier Catalogue of astronomical objects. Star formation is presently occurring in M16, which is located 7000 light-years from Earth in the constellation of Serpens Cauda (the Serpent’s Tail). Several bright, hot O and B stars are responsible for the ionizing radiation that causes the gases to glow. (Inset) Star formation is occurring inside these dark pillars of gas and dust. Intense ultraviolet radiation from existing massive stars off to the right of this image is evaporating the dense cores in the pillars, thereby prematurely terminating star formation there. Newly revealed stars are visible at the tips of the columns.