Spin-induced quadrupole moment based test for eccentric binaries

TL;DR

This paper extends the spin-induced quadrupole moment test for black hole nature to eccentric binaries, showing that neglecting eccentricity can cause significant biases in parameter estimation and black hole verification.

Contribution

It introduces a method to account for orbital eccentricity in gravitational wave tests of black hole nature, improving the accuracy of such tests.

Findings

Neglecting eccentricity causes biases in parameter inference.

Eccentric binaries can be misclassified as non-black hole systems.

Systematic errors from eccentricity can surpass statistical errors.

Abstract

The spin-induced quadrupole moment-based test of black hole nature is routinely used to probe the true nature of detected binary signals, assuming a circular orbit. We extend the applicability of the method to binaries in eccentric orbits. Considering simulated signals of varying masses, spins, and signal strengths, we demonstrate how the systematic errors resulting from neglecting orbital eccentricity compare with the statistical errors, using a semi-analytic Fisher matrix-based formalism that accounts for both current and future detectors. Further, we quantify the systematic errors by developing a Bayesian inference framework for the current detector network. The inspiral-only aligned spin gravitational wave waveform model for eccentric binaries, TaylorF2Ecc, is employed. For the current detector network, neglecting an initial eccentricity of $e_0^{\rm inj}=0.1$ defined at $20\,\mathrm {Hz} $ can lead to a serious bias in binary parameter inference. Notably, a nearly equal-mass, moderately spinning binary black hole in an eccentric orbit can be identified as a non-black hole binary with extreme spins and asymmetric masses. We demonstrate the criticality of biased estimates that may arise when neglecting the orbital eccentricity while performing tests of black hole nature and discuss prospects.