Why are there so many binary stars in the galaxy?
Quick Answer
Star-forming clouds often fragment into more than one collapsing clump, so two or more stars are frequently born together. That is why binary and multiple-star systems are common.
The Full Story
When a cloud of gas and dust collapses, it rarely forms just a single compact object. Small differences in density and angular momentum can cause the cloud to break into multiple fragments, each of which becomes a star. For massive stars, companions are especially common, and many stars that look single to the naked eye are actually binaries. Astronomers use binary stars to measure stellar masses very accurately, because orbital motion reveals the pull of gravity. In fact, our own nearest star system, Alpha Centauri, is a multiple-star system.
Key Facts
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