Binary Star Mass Calculator
Binary Star Mass
Calculate the total and individual masses of a binary star system from the orbital period and separation using Kepler third law.
Formula
Total Mass (solar) = a^3 / P^2 (Kepler third law in solar units); M1 = Total / (1 + q), M2 = Total x q / (1 + q)
Frequently Asked Questions
How do we measure binary star masses?
For visual binaries with known orbital period and separation, Kepler third law gives the total mass. Radial velocity measurements and the mass ratio allow determination of individual masses.
What fraction of stars are in binary systems?
Roughly half of all Sun-like stars exist in binary or multiple star systems. The fraction is higher for more massive stars and lower for red dwarfs.
What is the mass ratio?
The mass ratio q is the mass of the secondary (less massive) star divided by the mass of the primary. It ranges from 0 to 1, with 1 meaning both stars have equal mass.
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