Binary Stars bound by gravity and orbiting binary stars: multiple systems bound by gravity and orbiting each other around their center of mass (double star) Study of binary stars allows us to measure the masses of the stars since if we know how the stars orbit each other, we can calculate how much mass the stars must have to stay in those orbits. The mass of the star is the single most important characteristic of a star since it tells us everything else about its properties. The mass of a star tells you how luminous they are, what their lifetimes will be, how they will evolve, and how will eventually die.

Show balancing horse for center of mass

The orbital motion of binary stars affects the wavelengths of their spectral lines

Some binary stars eclipse each other Show Redshift 2 Movie on Binary Stars Show Redshift 1 Simulation on Binary stars