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Nebula

What is a nebula?
A nebula is a giant cloud of dust and gas in space. Some nebulae come from gas and dust ejected by the explosion of a dying star, such as a supernova. Other nebulae are regions where new stars begin to form. For this reason, some nebulae are called "star nurseries."

How do stars form in a nebula?

Nebulae are made of dust and gases. The dust and gases in a nebula are widely dispersed, but gravity can begin to pull together groups of dust and gas. As these groups get bigger and bigger, their gravitational pull gets stronger and stronger.

Eventually, the group of dust and gas becomes so large that it collapses under its own gravity. The collapse causes the material in the center of the cloud to heat up, and this hot core is the beginning of a star.