Binary Stars

This simulation solves the orbit of two stars exactly and draws both circling the barycenter, which sits closer to the heavier star. Controls set Star A mass, the mass ratio, the separation in astronomical units and the eccentricity, plus an optional mass-transfer stream through the L1 point. Readouts show the orbital period, current separation and each star's speed. Teachers can use it to demonstrate Kepler's third law and to show that neither star simply orbits the other.

• Raise Star A mass and watch the Orbital period readout shorten.
• Increase Separation a and check that P squared equals a cubed divided by the total mass.
• Set Eccentricity high and compare Speed star A at its closest and farthest points.
• Lower Mass ratio B/A and see the barycenter move towards the heavier star.
• Turn on Mass-transfer stream to see gas flow through the L1 point.

1. 1Explain that both stars in a binary orbit their common center of mass.
2. 2Apply Kepler's third law to relate period, separation and total mass.
3. 3Describe how speed changes along an elliptical orbit.
4. 4Identify the Roche lobe and L1 point as the route for mass transfer.

Questions teachers ask