Distinguishing Boson Stars from Black Holes and Neutron Stars from Tidal Interactions in Inspiraling Binary Systems

Abstract: Binary systems containing boson stars---self-gravitating configurations of a complex scalar field--- can potentially mimic black holes or neutron stars as gravitational-wave sources. We investigate the extent to which tidal effects in the gravitational-wave signal can be used to discriminate between these standard sources and boson stars. We consider spherically symmetric boson stars within two classes of scalar self-interactions: an effective-field-theoretically motivated quartic potential and a solitonic potential constructed to produce very compact stars. We compute the tidal deformability parameter characterizing the dominant tidal imprint in the gravitational-wave signals for a large span of the parameter space of each boson star model. We find that the tidal deformability for boson stars with a quartic self-interaction is bounded below by $\Lambda_{\rm min}\approx 280$ and for those with a solitonic interaction by $\Lambda_{\rm min}\approx 1.3$. Employing a Fisher matrix analysis, we estimate the precision with which Advanced LIGO and third-generation detectors can measure these tidal parameters using the inspiral portion of the signal. We discuss a new strategy to improve the distinguishability between black holes/neutrons stars and boson stars by combining deformability measurements of each compact object in a binary system, thereby eliminating the scaling ambiguities in each boson star model. Our analysis shows that current-generation detectors can potentially distinguish boson stars with quartic potentials from black holes, as well as from neutron-star binaries if they have either a large total mass or a large mass ratio. Discriminating solitonic boson stars from black holes using only tidal effects during the inspiral will be difficult with Advanced LIGO, but third-generation detectors should be able to distinguish between binary black holes and these binary boson stars.

Distinguishing Boson Stars from Compact Objects in Binary Systems

The paper titled "Distinguishing Boson Stars from Black Holes and Neutron Stars from Tidal Interactions in Inspiraling Binary Systems" presents a detailed study of boson stars (BSs) as potential mimickers of standard compact objects like black holes (BHs) and neutron stars (NSs) in gravitational wave (GW) signals. This investigation is crucial because the nature of compact objects can be probed by analyzing tidal interactions in inspiraling binary systems, detectable via GWs.

Key Objectives and Methods

The primary aim of the paper is to ascertain the viability of using tidal effects in the GW signals to differentiate BSs from BHs and NSs. The study focuses on two models of BSs, characterized by spherically symmetric configurations of scalar fields with specific self-interaction potentials: the quartic potential, and the solitonic potential. For each model, the authors compute the tidal deformability parameter, an essential quantity capturing the star's response to tidal fields, which manifests prominently in the GW signal during the inspiral phase.

The analysis is carried out across a broad parameter space, particularly covering the entire domain for the quartic potential and an extensive portion for the solitonic potential. Using fits convenient for data analysis, the tidal deformabilities are expressed across these configurations. The findings indicate that for BSs with quartic self-interactions, the tidal deformability is bounded below by approximately (\Lambda_\text{min} \approx 280), while for solitonic interactions, it is bounded by (\Lambda_\text{min} \approx 1.3).

Numerical Results and Implications

The paper provides ready-to-use numerical fits for practical applications, demonstrating that current GW detectors like Advanced LIGO, and forthcoming third-generation detectors, can potentially measure these tidal parameters. The authors employ a Fisher matrix analysis to assess the detectors' capability of distinguishing BSs from NSs and BHs. It is shown that BSs with quartic potentials can generally be distinguished from BHs and, under certain conditions, from NS binaries if the system has substantial total or asymmetric mass. However, differentiating solitonic BSs from BHs using solely tidal signatures during the inspiral might be challenging for Advanced LIGO, although third-generation detectors should improve this capacity.

Theoretical and Practical Implications

The research provides insights into the theoretical modeling of compact objects, expanding the scope beyond traditional astrophysical entities. The bounds on tidal deformability observed in the study underscore the distinct GW signal features that can be used to identify the nature of the compact bodies involved. Practically, these results highlight the utility of detections from GW observatories to probe new physics through exotic compact objects potentially present in the universe.

Future Prospects and Developments

The investigation sets a groundwork for more advanced studies that could integrate complete inspiral-merger-ringdown waveform models. This would refine the results further, especially with the incorporation of effects like spins, which significantly influence binary system dynamics. Future developments might include extensive numerical relativity simulations to capture the complex merger and post-merger dynamics of BSs. There is also potential for utilizing Bayesian data analysis methods to provide more precise estimates of distinguishability and to combine results from multiple GW events effectively, thereby enhancing the stringent testing of general relativity and exploring beyond-standard-model physics.

In summary, the paper presents a thorough investigation into the distinctive GW signatures of BSs, contributing to the broader goal of distinguishing astrophysical phenomena using next-generation sensors and establishing benchmarks for identifying exotic objects within the universe's compact entities.