qnm

Overview

qnm computes the quasinormal mode (QNM) frequencies of Kerr black holes using the Cook-Zalutskiy spectral approach. Alongside each frequency it returns the angular separation constant and the spherical-spheroidal mixing coefficients, which are needed to project the spheroidal harmonics onto the spherical basis.

The package ships with a precomputed cache of low-lying multipoles and overtones, so common modes are available without any on-the-fly root finding.

Installation

pip install qnm

The first time you use the cached modes, download the precomputed data:

import qnm
qnm.download_data()

Usage

Fetch a mode from the cache and evaluate it at a dimensionless spin a:

import qnm

mode = qnm.modes_cache(s=-2, l=2, m=2, n=0)
omega, A, C = mode(a=0.68)

print(omega)   # complex QNM frequency
print(A)       # angular separation constant

omega is the complex frequency (the imaginary part sets the damping time), and C holds the spherical-spheroidal mixing coefficients for the mode.

Examples

The repository includes notebooks demonstrating the cache, overtones, and mixing-coefficient usage.

Citing qnm

If you use qnm in your research, please acknowledge the Toolkit:

qnm also requests the following citation:

• Stein, qnm: A Python package for calculating Kerr quasinormal modes, J. Open Source Softw. 4(42), 1683 (2019)

See how to cite for the BibTeX entry and guidance.