Nebulae are said to have 2 different origins.
Nebulae created from the materials of the Universe itself, - Soon after the birth of Universe , atoms are created in the Universe and from these atoms the first dust and gas clouds are formed.
- The space between the stars within a galaxy is termed as interstellar space. This space is filled with molecules of gases and dust particles formed from the atoms.
- However, the density of this cloud of dust and gas is not uniform. Those regions which have a higher density are called molecular clouds. A molecular cloud comprises a large quantity of hydrogen, around 25 percent of helium and a small quantity of heavier elements.
- When the size and density of a molecular cloud increases to a certain level, then the condition is just right for the development of a star. At this stage the molecular clouds are termed as Nebulae.
Nebulae created from the matters ejected by the exploding stars,
The matters thrown out from the dying and exploding stars or supernova (later stage of star) gets clustered together to form clouds of dust and other particles forming Nebulae.
A nebula can be a mixture of primordial material as well as new material from previous stars.
