Using gravitational-wave observations and quasi-universal relations to constrain the maximum mass of neutron stars (1711.00314v2)

Abstract: Combining the GW observations of merging systems of binary neutron stars and quasi-universal relations, we set constraints on the maximum mass that can be attained by nonrotating stellar models of neutron stars. More specifically, exploiting the recent observation of the GW event GW 170817 and drawing from basic arguments on kilonova modeling of GRB 170817A, together with the quasi-universal relation between the maximum mass of nonrotating stellar models $M_{\rm TOV}$ and the maximum mass supported through uniform rotation $M_{\rm max}=\left(1.20^{+0.02}_{-0.05}\right) M_{\rm TOV}$ we set limits for the maximum mass to be $ 2.01^{+0.04}_{-0.04}\leq M_{\rm TOV}/M_{\odot}\lesssim 2.16^{+0.17}_{-0.15}$, where the lower limit in this range comes from pulsar observations. Our estimate, which follows a very simple line of arguments and does not rely on the modeling of the electromagnetic signal in terms of numerical simulations, can be further refined as new detections become available. We briefly discuss the impact that our conclusions have on the equation of state of nuclear matter.

• The paper combines gravitational-wave observations and quasi-universal relations to set constraints on nonrotating neutron stars' maximum mass.
• It determines the maximum mass to lie between approximately 2.01 and 2.16 solar masses, aligning with binary merger and pulsar data.
• The study enhances our understanding of the nuclear equation of state and informs predictions for neutron star mergers and gamma-ray burst outcomes.

Constraints on the Maximum Mass of Neutron Stars Using Gravitational-Wave Observations

The paper presented by Rezzolla, Most, and Weih addresses the ongoing challenge of determining the maximum mass of neutron stars by combining gravitational-wave (GW) observations with quasi-universal relations. The core focus is on leveraging data from the binary neutron star merger event GW170817, alongside observations from electromagnetic signals such as kilonova of GRB 170817A, to impose limitations on the maximum mass achievable by nonrotating neutron stars. This paper is crucial for refining our understanding of the equation of state (EOS) of nuclear matter, a fundamental aspect of astrophysics and high-density physics.

Numerical Analysis and Results

Central to the paper is the use of quasi-universal relations, which establish a consistent framework for analyzing the mass and rotational characteristics of neutron stars. By articulating a relationship between the maximum mass in nonrotating configurations (denoted as $M_{\text{TOV}}$) and those supported by uniform rotation, the authors constrain the maximum mass of a nonrotating neutron star to the range $$2.01_{-0.04}^{+0.04} M_\odot < M_{\text{TOV}} < 2.16_{-0.15}^{+0.17} M_\odot$$. This constraint aligns with observational data from massive pulsars and introduces a benchmark for future studies.

The research employs a simple yet robust theoretical framework that circumvents the need for detailed numerical-relativity simulations of the electromagnetic component, relying instead on kilonova modeling. This approach highlights a feasible methodology to continuously refine constraints as new gravitational-wave events are observed.

Theoretical and Practical Implications

The implications of this research span both theoretical and practical domains. Theoretically, it contributes significantly to the ongoing discourse around the EOS of nuclear matter, providing constraints that many proposed EOS models must satisfy. An important conclusion is the potential incompatibility of certain EOSs, such as the DD2 EOS, which predicts a maximum mass surpassing the upper constraint found in this paper.

Practically, the results guide astrophysical models concerning the fate of binary neutron star mergers, particularly in predicting the conditions under which these systems lead to either neutron stars or black hole formations. This knowledge underpins models of short gamma-ray bursts, further validating associations between electromagnetic signals and neutron star mergers.

Future Developments

The paper suggests that with additional gravitational-wave observations, especially those characterized by smaller mass systems than GW170817, tighter constraints on $M_{\text{TOV}}$ could be established. The authors advocate for the use of stacking techniques, emphasizing how these methods could be instrumental in analyzing upcoming data from gravitational-wave detections. As more observational data becomes available, the accuracy of the EOS constraints will improve, fostering advancements in both neutron star and dense matter physics.

In conclusion, this paper provides an essential contribution to neutron star research, demonstrating how universal relations can be effectively used in conjunction with multimodal observational data to enhance our understanding of these exotic objects' properties. The constraints outlined in this paper set the stage for further exploration into the upper mass limits of neutron stars, an area crucial for unraveling the nature of the dense matter constituting these astronomical bodies.