Where are stars born? (Beginner)

What is a massive cloud, believed to be the birthplace of the new stars?

Our galaxy, along with many others, contains many large clouds of gas and dust, mostly made up of hydrogen. These clouds are called "nebulae." If the cloud becomes large enough, then its own gravity begins to overcome the gas pressure, and the cloud can begin to collapse. As the cloud collapses, gravity, temperature, and pressure increase, until the cloud has collapsed enough to raise the temperature to that required to fuse (burn) the hydrogen. Once that fusion begins, the energy released halts the contraction, and the outer layers of gas are blown away. What's left is an incandescent ball of mostly hydrogen, set aglow by the fusion reactions in its core: a star.


This page updated on June 27, 2015

About the Author

Dave Kornreich

Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.