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Stars and stellar evolution
The early cosmos: Out of the darkness

Imagine a night sky without the twinkling light from stars and galaxies piercing the darkness. Astronomers believe that this was the bleak picture of the universe for at least a hundred million years after the "big bang," a tremendous explosion that produced time, space, and matter about 14 billion years ago.

Although no stars and galaxies existed just after the big bang, the young cosmos was anything but dull. It was humming with activity.

The big-bang explosion ejected intense radiation and energy. In the beginning, physical conditions were so extreme that matter as we know it today did not exist. When the universe was about one millionth of a second old, the temperatures and densities dropped enough for protons and neutrons — the building blocks of atoms — to form. Within the next few minutes, the nuclei of light elements, such as hydrogen, helium, lithium, and boron, were created. When the universe cooled to about 5,400 degrees Fahrenheit (3,000 degrees Celsius), atomic nuclei could finally capture electrons to form atoms. By 300,000 years, the universe was made up mostly of clouds of hydrogen and helium atoms.

As the universe expanded and cooled, some regions of space had slightly higher densities of hydrogen. As millions of years passed, the slight differences grew large, as dense areas drew in material because they had more gravity. Researchers have dubbed this period of coalescing the "dark ages."

"Fireworks Finale"

This is an artist's impression of how the very early universe might have looked as a firestorm of star formation took place. (Credit: Adolf Shaller)

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Dawn of stars

The dawn of light, called the "cosmic renaissance," began as hydrogen collapsed into small areas, eventually reaching the point at which the effect of gravity became great enough to trigger nuclear fusion reactions and form the first stars. These first-generation stars were probably born at least 100 million years after the big bang.

Today, astronomers who study distant galaxies are beginning to probe the cosmic renaissance. Roughly a thousand galaxies have been identified whose light left them when the universe was about 1 billion years old. At that time stars were forming at a rate about 10 times higher than in the present-day universe. Stars in that early period were making heavier elements, such as carbon and oxygen, which mixed with original gas from the big bang to create successive generations of stars.

At greater distances (looking farther back in time) our view becomes murkier; the number of known galaxies is smaller and their distances are more uncertain. Using the deepest images from the largest ground- and space-based telescopes, astronomers are just now beginning to see into the era when the first stars may have formed.


"Tales of … The early cosmos: Out of the darkness" explores the formation of stars in the early universe. The reading describes the cosmos from a time just after the big bang to the formation of the first stars.

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9-12, but the material can be adapted for use in other grades at the teacher's discretion
How to use in the classroom

Teachers can use this resource as:

A content reading selection. Teachers should discuss the meaning of unfamiliar vocabulary prior to having students read this selection.

An engagement activity. Have students read the selection. Ask them to describe the early universe or what it might have been like before and after stars formed.

An inquiry tool. Propose a question, such as, "What was the universe like before stars formed?" Have students read the selection and write down as many questions as they can about the information in the text.

A source of information. Students can describe the events that led up to the formation of the first stars.

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