This app models the evolution of a binary star system where the two stars are spinning. The stars' spins and orbital angular momentum influence each other through gravitomagnetic interactions. The colored arrows represent the stars' spin angular momentum vectors, and the white arrow is the system's orbital angular momentum (in the same units) but shrunk by a factor of 5 so that it does not dominate the scene. The fixed x, y, and z coordinate axes are red, green, and blue, respectively, and the z axis coincides with the initial direction of the orbital angular momentum. The circles show the stars' orbits.

The stars' orbital motion is much faster than the precession of their spins, so that orbital motion is not shown (simply imagine the stars whizzing around their orbit circles). The stars radiate both energy and angular momentum in the form of gravitational radiation, so the orbit becomes tighter with time. The model stops just before the stars coalesce (the approximations become inaccurate at this point). The direction of the system's total angular momentum is constant to this model's order of approximation.

Pressing the "Run" button will start the evolution. Pressing the same button (now labeled "Stop") will freeze the evolution, and pressing "Run" again will continue the evolution from the system's current state (ignoring any parameters you may have changed when stopped). Use the Reset button to re-initialize the model after you have changed parameter values (pressing this button will also hide the coalescence message).

In the GR units used by this program, masses, times, and distances are measured in solar masses (where 1 solar mass = 1477 m = 4.92 µs), and angular momentum has units of solar masses squared. The X1 and X2 values specify the magnitude of the stars' spins a fraction of the maximum possible spin: these numbers should be positive numbers between 0 and 1. The ratio r/m is a unitless ratio in GR units, and should be greater than 30 (one is too close to coalescence when r/m < 30). ThN and PhN variables express the altitude and azimuth angles of the Nth star's spin vector. (The arrow lengths and orbit sizes are correct for purposes of comparison, but calculating their actual values in GR units from the display is difficult and not worth the effort.)

Written by Nikolas Papastavrou in July 2017 using modeling code developed by Kiran Siebel, with modifications by Tom Moore.