Expert: Jayendra Upadhye - 1/31/2005

Question
How can an astronomer recognize a double star from the characteristic frequencies of the light that reaches him from its member stars?

Answer
Hi Michael,
That can be found by studying the "wobble" of the star.
Light from a double star (where one component is too faint or masked by the brilliance of its partner, or is a black hole, or the said binary is too far to be resolved into individual stars), undergoes a periodic red and blue shift due to the doppler effect. when the brilliant star approaches us, its light undergoes a blue shift, and when it is moving away from us, it undergoes a red shift.
By studying this periodic shift or wobble, scientists can tell a lot about the separation of the components and their comparative masses.
Jayen