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Why is our Sun Alone?

-- | February 7, 2014

Question: As per observations, most of the stars are born in clusters (i.e. in open clusters). Then why our sun is an isolated star with no companions? — Vinod

Answer: Our Sun was probably born in a group of stars, but later escaped from or simply fell-out of this group. Our Sun may have been pushed away due to an encounter with another star or a much larger object, such as a molecular cloud. Or, and this scenario is a bit more likely, our Sun simply didn’t keep pace with its birth mates. Since it takes about 135 million years for our Sun to orbit our Galaxy, small differences in the rate at which our Sun and the stars that were born with it will spread out over the 5 billion year age of our Sun. Stars travelling slightly slower than our Sun will get left behind, which those stars that are travelling slightly faster will leave our Sun in the dust (interstellar, that is). In the end, the result is a dispersed group of stars who once shared a common beginning.

Jeff Mangum

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