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Star Formation

Stars are formed from a nebula, and have different life cycles depending on their size.

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14.4 Star Formation

Can you see stars being born?

On a dark night you can practically watch stars being born. The fuzzy area in the sword in the constellation Orion is the Orion nebula. A close up shows the nebula with around 3,000 stars. New stars are being born there.

Star Lives

Stars have a life cycle, just like people. Stars are born, grow, change over time, and eventually grow old and die. Most stars change in size, color, and class at least once in their lifetime. What astronomers know about the life cycles of stars is because of data gathered from visual, radio, and X-ray telescopes.


Stars are born in a cloud of gas and dust called a nebula. Our Sun and solar system formed out of a nebula. A nebula is shown in Figure below.

Stars are forming in the Rosette Nebula.

The Pillars of Creation, seen in the Figure below, are within the Eagle Nebula. The pillars are thought to be a large region where stars are forming. The dark areas may be stars that are about to begin.

In the Pillars of Creation gas and dust come together as a stellar nursery.

Star Formation

For a star to form, gravity pulls gas and dust into the center of the nebula. As the material becomes denser, the pressure and the temperature increase. When the temperature of the center becomes hot enough, nuclear fusion begins. The ball of gas has become a star!

Our Sun was probably born in a nebula like Orion in the top image.


  • nebula: A cloud of dust and gas where stars form.


  • Stars form in a nebula.
  • A nebula is a cloud of dust and gas.
  • Nebulae can be spotted with the naked eye or simple telescopes.


Use this resource to answer the questions that follow.

Stellar Evolution at http://www.youtube.com/watch?v=XVB5gepkXC4 (8:23)

  1. What is stellar evolution?
  2. Where are stars born?
  3. What are nebula?
  4. What force compresses the dust and gas?
  5. Which type of stars live the longest?
  6. How long do most main sequence stars live?
  7. What happens to high mass stars?
  8. What is a hyper-nova?
  9. What is a neutron star?
  10. What is a black hole?


  1. What is a nebula?
  2. How do stars form?
  3. How did our Sun form?

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