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Binary stars
Intermediate
Two stars orbiting their common centre of mass.
Two stars orbiting a common centre. The orbital data give masses via Kepler's third law: M₁ + M₂ = 4π²a³/GT².
Sirius A and B: T = 50 years.
Mass ratio from the distances to the centre of mass.
In more detail
Binary stars orbit a common centre of mass, and their orbits follow Kepler's laws and gravitational dynamics. Measuring their orbits gives the masses of the stars.
Real-world uses
- Astronomers weigh stars by measuring binary orbits.
- Gravitational wave sources are often binary systems.
- Many stars in the sky are binaries, and measuring their orbits lets astronomers weigh each star.
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Frequently asked questions
Are most stars in binaries?
Many stars are in binary or multiple systems, though exact fractions vary by type.
How is the mass found?
From the orbital period and size, using Kepler's third law.
Do binary stars orbit a common point?
Yes. Both stars orbit their common centre of mass, which lies closer to the more massive star.
Related topics in Gravitation & Orbits
Lagrange points · Two-body problem · Effective potential · Weighing the Sun and planets · Gravitational lensing · Gravitational waves