Nebulae

A nebula is an cloud of gas that is the beginning stage in the life of a star (here). Nebulae form when interstellar medium clumps together and attracts more matter gravitationally. Eventually, gravity contracts the matter so much that that a infant star forms inside the nebula. At this point, the nebula is illuminated and therefore telescopes can spot it. Another way for a nebula to form is when a supernova explodes and leaves behind a cloud of gas, causing a chain reaction that leads to a nebula. Yet another type of nebula can form is from a smaller star such as our Sun. As the the Sun becomes a red giant, it lets off its outer layers, and these, later, can clump together, thereby forming a nebula. Nebulae can be large or small, depending on the amount of gas, and therefore the number of stars formed can vary as well.

Many types of nebulae exist, but most of them fall under the broader category of diffuse nebulae. The term diffuse nebula merely means that the nebula is irregular and has no exact edge or boundary. Diffuse nebulae are divided into subcategories based on how they are visible.

• Emission Nebula:  A nebula that is visible due to the ionized Hydrogen and Helium within it
• Reflection Nebula: A nebula that reflects the light of a nearby star
• Dark Nebula: A nebula that would normally be invisible, but is illuminated by a star behind it.

Nebulae are among the most beautiful objects in the Universe.



The Helix Nebula.



The famous Pillars of Creation seen in the Eagle Nebula.