Glossary of Astronomical Terms/binary star
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A binary star system consists of two stars that are orbiting their common center of mass.
It is believed that as many as one quarter of all apparent stars are actually binary systems. As many as 10% of these binary systems may actually have more than two stars as in the Alpha Centauri system. The distances between stars in binary systems vary widely; sometimes they seem almost to touch, and other times their association may not be readily apparent. In the illustration below, the two stars in a binary system are close enough together that the larger one draws material off the atmosphere of the smaller one.
The gravitational interaction of binary stars allows astronomers to calculate the masses of these stars, something which is not possible with singular stars.
Yes, since they orbit their center of mass, if one were to be "bumped" out of positon, the center of mass would move accordingly, and so they would continue to orbit opposite each other.
The less massive one since its orbit is larger but it must complete it in the same period of time as the more massive star completes its smaller orbit.
