Initial data for binary neutron stars with adjustable eccentricity

Understand

Binary neutron stars in circular orbits can be modeled as helically symmetric, i.e., stationary in a rotating frame.

• This symmetry gives rise to a first integral of the Euler equation, often employed for constructing equilibrium solutions via iteration.
• For eccentric orbits, however, the lack of helical symmetry has prevented the use of this method, and the numerical relativity community has often resorted to constructing initial data by superimposing boosted spherical stars without solving the Euler equation.
• The spuriously excited neutron star oscillations seen in evolutions of such data arise because such configurations lack the appropriate tidal deformations and are stationary in a linearly comoving---rather than rotating---frame.