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Modern cosmologies suggest that the universe was quite dark for much of its first billion years. During these dark ages, the universe contained clouds of hydrogen gas, but little else—the first stars did not form until several hundred million years had passed. Once the cosmic star-making machinery got going, however, it churned out giant balls of burning gas with a passion—there are now thought to be 1021 stars in the observable universe. After studying the ages of the stars in nearly 100,000 galaxies, astrophysicist Alan Heavens estimated the rate at which the universe formed stars at different periods in its history. His results challenge the traditional view and suggest that large and small galaxies may have formed most of their stars at different times in the past.
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