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".
Nebulae are made of dust and gases - mainly hydrogen and helium. The dust and gases in a nebula are widely dispersed, but gravity can begin to pull dust and gas groups together. As these clumps get bigger and bigger, their gravitational force becomes stronger and stronger.
Eventually, the dust and gas group becomes so large that it collapses under its own gravity. The collapse causes the material in the center of the cloud to get hot, and this hot core is the beginning of a star.
Nebulae exist in the space between the stars, also known as interstellar space.
Astronomers use very powerful telescopes to take pictures of distant nebulae.
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