Eccentricity in Binary Neutron Star Parameter Estimation Introduces Systematic Bias up to 0.124022, Study Shows

Gravitational waves offer a unique window into the most extreme events in the universe, yet accurately interpreting these signals requires precise modelling of the source, particularly for merging binary neutron stars. Eunjung Lee, Hee-Suk Cho, and Chang-Hwan Lee, all from Pusan National University, investigate systematic errors that arise when analysing these signals, specifically those caused by unaccounted-for eccentricity in the neutron stars’ orbits. Their work extends previous research by incorporating the effects of stellar spin, a crucial factor in realistic scenarios, and demonstrates how ignoring eccentricity can introduce significant biases when estimating key parameters like mass, spin, and tidal deformability. By employing a robust analytical method and validating it with numerical simulations, the team reveals the extent of these biases and their implications for accurately determining the fundamental properties of neutron stars, ultimately improving the reliability of gravitational wave astronomy.

Eccentric Orbits Bias Neutron Star Parameters

This research investigates how eccentric, or non-circular, orbits affect the accuracy of gravitational-wave parameter estimation from merging binary neutron stars. Scientists focused on how using waveform models designed for perfectly circular orbits can introduce errors when applied to systems with even slight eccentricity. The study explores biases in parameter estimation, particularly in determining the equation of state, which describes the behavior of matter inside neutron stars. Researchers employed the Fisher Information Matrix and full Bayesian parameter estimation techniques to quantify these biases, validating the results with more complex numerical simulations.

The team generated a large number of simulated binary neutron star mergers, varying the masses, spins, and orbital eccentricities to comprehensively assess the impact on parameter estimation. Results demonstrate that using circular waveform models to analyze eccentric signals introduces significant biases in estimated parameters, not simply random errors, but systematic distortions consistently skewing the results. These biases are particularly pronounced in the estimation of neutron star masses and tidal deformability, a measure of how much the star is distorted by its companion’s gravity, both crucial for constraining the equation of state. The magnitude of these biases increases with the level of eccentricity, meaning even small deviations from a perfect circle can produce noticeable errors. Researchers predict these biases will be even more severe with the next generation of gravitational-wave detectors, which will be sensitive to signals from more distant and eccentric systems. This work emphasizes the importance of verifying the reliability of analytical methods with full numerical simulations to ensure accurate inferences about neutron star properties.

Eccentricity and Spin Bias Gravitational Wave Parameters

This research presents a detailed investigation into systematic biases introduced when analyzing gravitational-wave signals from binary neutron star systems, specifically addressing the impact of eccentricity and stellar spin. Researchers employed the TaylorF2 waveform model and the Fisher-Cutler-Vallisneri method to simulate signals and meticulously calculate biases in estimated parameters, validating the results with more complex numerical simulations. The study generated a large number of binary neutron star sources, randomly distributed with neutron star masses between 1 and 2 solar masses, effective spins ranging from -0. 2 to 0.

2, and eccentricities up to 0. 024. Results demonstrate that biases in chirp mass, symmetric mass ratio, and effective spin exhibit predictable trends with increasing eccentricity, indicating a relatively weak dependence on these parameters. However, biases in effective tidal deformability, a crucial parameter for probing the equation of state of neutron stars, are widely distributed and strongly dependent on both mass and spin parameters at a given eccentricity. Specifically, the team found that parameter estimation using non-eccentric waveforms for eccentric binary neutron star signals can yield false predictions for the neutron star equation of state, potentially estimating component masses significantly outside the typical 1 to 2 solar mass range. This research highlights the importance of accurately modeling eccentricity in gravitational-wave data analysis to ensure reliable inference of neutron star properties and accurate constraints on the equation of state. The study provides a crucial step towards more precise and accurate astrophysical measurements using gravitational-wave observations.

Eccentricity Biases in Neutron Star Parameters

This research demonstrates that even small amounts of eccentricity in gravitational wave signals from binary neutron star systems can significantly shift estimates of key parameters, including mass, spin, and tidal deformability, away from their true values. By employing both the Fisher-Cutler-Vallisneri method and full Bayesian parameter estimation techniques, scientists calculated systematic biases arising from the use of non-eccentric waveforms to analyze eccentric signals. The study generated a large number of simulated binary neutron star mergers, varying mass, spin, and eccentricity, to map the distribution of these biases across a realistic parameter space. Results indicate that while biases in chirp mass, symmetric mass ratio, and effective spin show a relatively weak dependence on eccentricity, biases in tidal deformability are highly sensitive to both mass and spin parameters.

Importantly, the team found that these biases consistently lead to an overestimation of mass asymmetry between the neutron stars, potentially leading to inaccurate conclusions about the equation of state governing neutron star matter. For example, parameter estimation using non-eccentric waveforms can incorrectly favor one equation of state model over another, even when the true signal contains eccentricity. The authors emphasize the importance of verifying the reliability of analytical methods with full numerical simulations to ensure accurate inferences about neutron star properties. Future work should focus on refining parameter estimation techniques to account for eccentricity and improve the accuracy of astrophysical measurements using gravitational-wave observations.