Main Sequence Stars - stars like the Sun
Welcome to Quatr.us Study Guides!

Main Sequence Stars

Milky Way
A starry sky with the Milky Way galaxy
(thanks to Bernd Nies)

Nine out of ten stars that you see in the sky are main-sequence stars, and our sun is one of them. Most main-sequence stars probably started out as brown dwarfs, and then succeeded in getting enough mass together to begin a nuclear fusion reaction inside them. It's the energy from this nuclear fusion reaction, changing hydrogen atoms into helium atoms and releasing the extra energy, that makes the stars shine.

What holds a star together is a balance of two forces pushing against each other. Gravity pulls the star's atoms in towards the center, just as gravity pulls you toward the Earth. The fusion reaction going on inside the star pushes the atoms away from the center, towards space. When these two forces are equal, the star can continue existing. Generally the two forces do stay in balance. That's because whenever the fusion reaction begins to slow down, it doesn't push out as much. Then the gravity can push in more, and that forces the hydrogen atoms closer together, which starts up the fusion process again and restores the balance.

Because the forces pushing in and out are the same in all directions, stars are basically shaped like balls. But because stars also spin around, centrifugal force tends to flatten out the ball a little, so most stars are a little thicker around the middle than they are at the top or bottom.

Main-sequence stars fall out of balance when they have used up all of their hydrogen fuel. Bigger stars, which burn hotter, use up their fuel faster, and smaller, cooler stars last longer. The biggest main-sequence stars last only a few million years, while the smallest main-sequence stars last over a trillion years. Once the star has used up all its fuel, it expands into a supergiant star.

Bibliography and further reading about stars:

Star Types
Space
Physics
Quatr.us home


LIMITED TIME OFFER FOR TEACHERS: Using this article with your class? Show us your class page where you're using this article, and we'll send you a free subscription so all your students can use Quatr.us Study Guides with no distractions! (Not a teacher? Paid subscriptions are also available for just $16/year!)
Please help other teachers and students find us: link to this page from your class page.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter, or buy her book, Vandals to Visigoths.
Cite this page
  • Author: K.E. Carr
  • Title:
  • Site Name: Quatr.us Study Guides
  • Publisher: Quatr.us
  • Date Published:
Proud of your class page, homework page, or resource page? Send it in and win a Quatr.us "Great Page!" award!
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Comment on This Article

Does your class page honor diversity, celebrate feminism, and support people of color, LBGTQ people, and people with disabilities? Let us know, and we'll send you a Diversity Banner you can proudly display!
Looking for more?
Quatr.us is loading comments...
(Comments will appear after moderation, if they are kind and helpful. Feel free to ask questions, and we'll try to answer them.)
Cite this page
  • Carr, K.E. . Quatr.us Study Guides, . Web. 23 March, 2017
ADVERTISEMENT