NEBULAE If we translate the Latin word ‘nebula’, it would simply mean ‘cloud’. The nebula that we are about to talk about, however, is so much more than just a cloud. A nebula is an interstellar cloud in outer space that is made up of dust, hydrogen and helium gas, and plasma. It is formed when portions of the interstellar medium collapse and clump together due to the gravitational attraction of the particles that comprise them. Many nebulae or stars form from the gravitational collapse of gas in the interstellar medium or ISM. As the material collapses under its own weight, massive stars may form in the center, and their ultraviolet radiation ionizes the surrounding gas, making it visible at optical wavelengths. Examples of these types of nebulae are the Rosette Nebula and the Pelican Nebula. 1. Classical types Objects named nebulae belong to four major groups. Before their nature was understood, galaxies ("spiral nebulae") and star clusters t...
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