A Star Is Born

It all begins with an unimaginably cold cloud. This cloud contains the seeds of whole new worlds – stars and planets about to be born.

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Molecules of hydrogen and helium gas, which normally zip around at high speeds, slow down and clump together because of gravity. Tiny grains of silicates, iron and carbon-rich material — together classified simply as "dust" — send some of the gas’s energy back out into space, making the cloud even colder. The dust grains spiral into the central knot of matter, like water running down a drain.

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As this pocket of the cloud contracts and thickens, a bright, hot ball begins to form at the center as more gas and dust are pulled in. Gravity is waging a battle against the pressure of gas and magnetic fields, and gravity is winning.

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While the infant star takes shape, the material spiraling inward flattens into a pancake-like structure known as an accretion disk.

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Why does this happen? The gravitational tugs of the galaxy’s billions of stars may have accelerated and shocked the gas. Or, maybe two clouds are bumping into each other, causing pockets of gas to coalesce. But sometimes, the catastrophic explosion of a massive star drives strong winds of material into a star-forming cloud — a death resulting in a new birth.

NASA