Category:Nebula

A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Nebulae are often star-forming regions, such as in the Eagle Nebula. In these regions the formations of gas, dust, and other materials "clump" together to form larger masses, which attract further matter, and eventually will become massive enough to form stars. The remaining materials are then believed to form planets, and other planetary system objects.

Formation
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. The size of these nebulae, known as HII regions, varies depending on the size of the original cloud of gas. New stars are formed in the nebulas. The formed stars are sometimes known as a young, loose cluster.

Some nebulae are formed as the result of supernova explosions, the death throes of massive, short-lived stars. The materials thrown off from the supernova explosion are ionized by the energy and the compact object that it can produce.?

Other nebulae may form as planetary nebulae. This is the final stage of a low-mass star's life, like Earth's Sol. Stars with a mass up to 8–10 solar masses evolve into red giants and slowly lose their outer layers during pulsations in their atmospheres. When a star has lost enough material, its temperature increases and the ultraviolet radiation it emits can ionize the surrounding nebula that it has thrown off. The nebula is almost 97% hydrogen and 3% helium, plus trace amounts of other elements.