A nebula is a giant cloud of dust and gas in space. Some nebulae come from the gas and dust thrown out by the explosion of a dying star, such as a supernova. For this reason, some nebulae are called “star nurseries.”
Stars are born within the clouds of dust and scattered throughout most galaxies. Turbulence deep within these clouds gives rise to knots with sufficient mass that the gas and dust can begin to collapse under its own gravitational attraction. As the cloud collapses, the material at the center begins to heat up. Known as a protostar, it is this hot core at the heart of the collapsing cloud that will one day become a star. Not all of this material ends up as part of a star — the remaining dust can become planets, asteroids, or comets or may remain as dust.
