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updated: 11/1/2011 7:44 AM

Gas, dust and energy make up the complex life of stars

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  • A photo from a previous star show at the Adler Planetarium in Chicago.

    A photo from a previous star show at the Adler Planetarium in Chicago.
    Courtesy of Adler Planetarium


You wanted to know

Jen Janik's third-graders at Big Hollow Elementary in Ingleside asked, "How do stars form in space?"

Coming full circle, a star begins with gas and dust, and when it dies, it returns much of the gassy mixture back to space.

"We think the very first stars formed very early on in the history of the universe," said Geza Gyuk, director of astronomy at the Adler Planetarium. "Those stars may have been very different from today's stars."

Most galaxies have clouds of dust and gas.

"Occasionally, one of these clouds, or part of a cloud, will be squeezed, perhaps by a collision with another cloud or by the shock from an exploding star," Gyuk said. "The part of the cloud that is squeezed becomes denser, gaining more material and stronger gravity."

The cloud continues to pull in more material, becoming more compact and hotter. Then it collapses. The center of the cloud becomes a star.

Sometimes the cloud produces a few stars. The newborn star is called a protostar. Planets, asteroids and comets also can get their start in the swirling disk surrounding a protostar.

A star's life expectancy is billions of years. During that lifetime, its job is to transform hydrogen into helium, producing energy.

The energy required to support the star's structure eventually will be exhausted, and this end-of-life action will allow new nuclear reactions that "manufacture" carbon, nitrogen, iron and other chemicals, depending on the mass of the star.

The new temporary source of energy will force the star to expand. This overinflated star in its final stages of life is called a red giant.

"Stars are everywhere. They form all over the Milky Way and in other galaxies," Gyuk said. "The farthest possible that we've seen is 14 billion light years away."

How many stars are in the universe? There are too many for scientists to count, so a math model is used to estimate the number of stars. The answer is 10 times 10 (100), 21 times, or about a billion trillion.

How do you find a star? Astronomers developed a map of 88 constellations -- sections of the sky where stars are located. Some of the section names are probably familiar to you -- Andromeda, Ursa Major and Draco.

Within these constellations are asterisms -- collections of identifiable stars. Two you've probably heard of are the Big Dipper and Orion's belt.

Learn more about stars, planets, asteroids, comets and other space objects at the Adler Planetarium. See the Adler website at for more information.

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