The Orion Nebula
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Nebulae - The Dust of Stars

Why would we call nebulae stardust? Because the gas of which they are composed both creates and is created by stars. Stars are composed of very dense, high temperature gas. Nebulae are also composed of gas, but they are cooler and less dense. Water is at least 1,000,000,000,000,000 times as dense as the gas found in nebulae.

Nebulae come in a variety of shapes. But their appearance is usually linked to the energy source which is lighting them up. For every region of gas which we can detect in the optical region of the spectrum, much more gas exists which is not easily visible. Something must happen for the nebulae to reveal themselves.

So, what happens to make nebulae glow? It depends on the type of nebulae. Some are involved in the formation of new stars. These are stellar nurseries called HII regions. The young stars found in HII regions are extremely hot and provide a lot of energy for lighting up nebulae. Some nebulae are the products of stellar death: supernova remnants and the planetary nebulae surrounding white dwarfs.

Some types of gas clouds are not visible in the optical regions of the electromagnetic spectrum. We need to explore some other wavelengths to observe these type of gas clouds. For example, neutral hydrogenemits energy in the radio region of the electromagnetic spectrum. Dust absorbs the optical and ultraviolet light of stars and re-emits it as infrared radiation.

Last modified January 13, 2006 by Travis Metcalfe.

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