H II region is the birthplace of stars. They are formed when a vast molecular cloud collapses under its own gravitational force, often caused by the explosion of a nearby supernova. Cloud collapsed and fragmented, creating hundreds of new stars. Newly formed stars ionize the surrounding gas is creating the emission nebula.Nebula is formed by the death of another star. A star that is undergoing a transition to the white dwarf stage expel its outer part to form planetary nebulae. Nova and supernova can also create a nebula known as nova and supernova remnant remnant.