Binary Star System
A stellar system consisting of two gravitationally bound stars orbiting around their common center of mass.
Governing formula
P² = (4 π² / (G (M₁ + M₂))) a³ (Kepler's 3rd Law)
SI unit
AU (Semi-major axis) & Years (Period)
In depth
Binary systems allow direct measurement of stellar masses using Kepler's third law. Close binary systems can undergo mass transfer via Roche lobe overflow, producing Type Ia supernovae, X-ray binaries, or millisecond pulsars.
Examples in the real world
Cygnus X-1, a high-mass X-ray binary consisting of a blue supergiant star accreting matter onto a stellar-mass black hole.