The above images exhibit the stars used in the calculation when they are isolated and in spherical equilibrium. The stars are modeled in full general relativity as polytropes with a polytropic index n=1. For this calculation, the stars were created with a radius R = 11.4 M, where M is the total mass-energy, and with a rest mass M0 that is 55% of the maximum allowed rest mass of an isolated, nonrotating star.
Here we display the density profile of the isolated neutron star as seen in the equatorial plane. Numbers are in nondimensional units.
Two identical polytropes of the type described above are now placed in a corotating circular binary orbit. They are separated by a coordinate distance r = 27.4 M0 initially, where M0 is the mass of an individual neutron star.
We use the quantity ZA, as defined in the above image, to parametrize the binary separation. This parameter is defined so that infinitely separated binaries correspond to ZA = 1, while grazing binaries correspond to ZA = 0.