Units and Conventions

Geometric units

All internal calculations use geometric units where G = c = 1:

Quantity	Unit	Symbol
Mass	Total mass M	M
Time	M	t
Energy	M	E
Angular momentum	M2	J
Linear momentum	M	P
Velocity (kick)	c	v
Spin (dimensionless)	S / M2	chi

Kick velocity in km/s

The kick velocity can also be reported in km/s using the conversion factor from lal (speed of light). This requires lal to be installed:

pip install gw_remnant[lal]

The converted value is available via:

props = calc.get_remnant_properties()
print(props["remnant_kick_kmps"])  # km/s

Sign conventions

• Mass ratio: q = m₁ / m₂ with m₁ >= m₂, so q >= 1.

• Spin vectors: Cartesian [sx, sy, sz], dimensionless. Aligned-spin systems have only a z-component.

• Time alignment: t = 0 corresponds to the peak amplitude of the (2, 2) waveform mode.