spectre.Pipelines.EccentricityControl.InitialOrbitalParameters

Functions

initial_orbital_parameters(mass_ratio, ...)

Estimate initial orbital parameters from a Post-Newtonian approximation.
spectre.Pipelines.EccentricityControl.InitialOrbitalParameters.initial_orbital_parameters(mass_ratio: float, dimensionless_spin_a: Sequence[float], dimensionless_spin_b: Sequence[float], eccentricity: float | None = None, mean_anomaly_fraction: float | None = None, separation: float | None = None, orbital_angular_velocity: float | None = None, radial_expansion_velocity: float | None = None, num_orbits: float | None = None, time_to_merger: float | None = None) → Tuple[float, float, float]

Estimate initial orbital parameters from a Post-Newtonian approximation.

Given the target eccentricity and one other orbital parameter, this function estimates the initial separation ‘D’, orbital angular velocity ‘Omega_0’, and radial expansion velocity ‘adot_0’ of a binary system in general relativity from a Post-Newtonian (PN) approximation. The result can be used to start an eccentricity control procedure to tune the initial orbital parameters further.

Currently only zero eccentricity (circular orbits) are supported, and the implementation uses functions from SpEC’s ZeroEccParamsFromPN.py. This should be generalized.

Parameters:

  • mass_ratio – Defined as q = M_A / M_B >= 1.

  • dimensionless_spin_a – Dimensionless spin of the larger black hole, chi_A.

  • dimensionless_spin_b – Dimensionless spin of the smaller black hole, chi_B.

  • eccentricity – Eccentricity of the orbit. Specify together with _one_ of the other orbital parameters. Currently only an eccentricity of 0 is supported (circular orbit).

  • mean_anomaly_fraction – Mean anomaly of the orbit divided by 2 pi, so it is a number between 0 and 1. The value 0 corresponds to the pericenter of the orbit (closest approach), the value 0.5 corresponds to the apocenter of the orbit (farthest distance), and the value 1 corresponds to the pericenter again. Currently this is unused because only an eccentricity of 0 is supported.

  • separation – Coordinate separation D of the black holes.

  • orbital_angular_velocity – Omega_0.

  • radial_expansion_velocity – adot_0.

  • num_orbits – Number of orbits until merger.

  • time_to_merger – Time to merger.

Returns: Tuple of the initial separation ‘D_0’, orbital angular velocity

‘Omega_0’, and radial expansion velocity ‘adot_0’.