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The Question

(Submitted March 21, 1999)

I'm curious about why there is such a large percentage of binary star systems. What are the best theories about the reason for this? Are there any websites you would recommend to research this?

The Answer

A major barrier to star formation is angular momentum. A gas cloud collapsing to form stars can convert its angular momentum into the rotation of the stars, both as individuals and as members of larger groups rotating about a common center of mass. The binary stars tend to gain energy (i.e. become closer together and shorten their periods) through collisions with single stars in dense stellar environments, thus making it more difficult for single stars to form.

I hope this helps,

Tim Kallman
for Ask an Astrophysicist

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