How Do Astronomers Weigh a Star?

If a star cannot be placed on a scale, how can a binary orbit reveal its mass?

Measure orbital period and separation, locate the centre of mass, and turn motion into a dynamical mass estimate.

A warm amber star and a smaller blue-white companion orbit a marked common centre of mass along restrained elliptical paths. — Vastward scientific reconstruction. Binary motion lets astronomers estimate mass; the orbit, sizes, colours, and separation are illustrative rather than one observed system.

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