Nebulae form some of the most beautiful formations in the universe. A nebulae is usually the end product of a star, but they can also be a place of star formation. There are four main types of nebulae: diffuse nebulae, planetary nebulae, dark nebulae, or supernova remnants. These different types of nebulae vary greatly on looks and form.
Diffuse nebula are thin but widespread cloud accumulations of dust and gas. Sometimes these nebulae can be the place of star formation. The young stars they create produce a high amount of energy that "excites" the dust and gas to make it shine. A nebulae like this is called an emission nebulae. If the stars fail to produce the high amount of energy, the cloud would instead reflect the light of the stars, making the gas shine. These are called reflection nebulae. Next are the planetary nebulae. When a star has used up all of its nuclear fuel, it blows most of its mass into space in the form of gas and dust.The energy from the star's exposed core causes the gas and dust to shine.
A supernova remnant is a nebula created from the violent explosion of a supermassive star. The explosion can be 10 billion times brighter than the Sun, and ejects most of the star's matter out into space. Dark nebulae are unique in that they cannot be seen by light from nearby and imbedded stars. The nebulae can only be seen as a profile traced against the light of objects behind it. An excellent example of a dark nebula is the Horsehead Nebula.
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