Gravitational-wave constraints on the neutron-star-matter Equation of State (1711.02644v2)

Abstract: The LIGO/Virgo detection of gravitational waves originating from a neutron-star merger, GW170817, has recently provided new stringent limits on the tidal deformabilities of the stars involved in the collision. Combining this measurement with the existence of two-solar-mass stars, we generate a generic family of neutron-star-matter Equations of State (EoSs) that interpolate between state-of-the-art theoretical results at low and high baryon density. Comparing the results to ones obtained without the tidal-deformability constraint, we witness a dramatic reduction in the family of allowed EoSs. Based on our analysis, we conclude that the maximal radius of a 1.4-solar-mass neutron star is 13.6 km, and that smallest allowed tidal deformability of a similar-mass star is $\Lambda(1.4 M_\odot) = 120$.

• The paper introduces a novel methodology combining GW170817 tidal deformability data with two-solar-mass observations to narrow the neutron star equation of state.
• It employs segmented polytropic interpolation between low-density Chiral Effective Theory and high-density perturbative QCD to bridge theoretical predictions.
• Results constrain a 1.4-solar-mass neutron star to a maximum radius of 13.6 km with a tidal deformability lower bound of 120, informing dense matter research.

Gravitational-wave Constraints on the Neutron-star-matter Equation of State

The paper "Gravitational-wave constraints on the neutron-star-matter Equation of State" presents a comprehensive paper of the implications of recent gravitational wave observations for our understanding of the equation of state (EoS) of neutron star matter. The work tackles a fundamental problem in astrophysics and nuclear physics: constraining the properties of dense nuclear matter under extreme conditions, as present in neutron stars.

Overview of the Methodology

The authors focus their analysis on results derived from the LIGO/Virgo observation of the gravitational wave event GW170817, which provides constraints on the tidal deformabilities of neutron stars involved in a merger. By integrating this observational data with the existence of two-solar-mass neutron stars as previously observed, they construct a family of EoSs that bridge theoretical predictions at low and high baryon densities. The computational approach involves dividing the relevant density range into segments, utilizing polytropic forms in each for interpolation between the constraints provided by low-density Chiral Effective Theory (CET) and high-density perturbative QCD (pQCD).

Results and Implications

The inclusion of the tidal deformability constraints leads to a significant narrowing of the allowed EoS parameter space, resulting in a dramatic reduction in the family of permissible EoSs. Specifically, the authors find that the EoS must be consistent with a maximal neutron star radius of 13.6 km for a 1.4-solar-mass star, with a lower bound on the tidal deformability set at $\Lambda(1.4 M_\odot) = 120$. These results are strengthened by the corroboration of their constraints with prior studies, notably the observational bounds on two-solar-mass stars.

The implications of these findings are multi-faceted. Practically, they offer deeper insights into neutron star structure, enhancing our understanding of the macroscopic properties such as mass-radius relationships. Theoretically, they challenge and constrain models of nuclear matter under extreme conditions, imposing stringent boundaries on potential theories at intermediate densities where neither CET nor pQCD alone are feasible.

Future Directions

The paper anticipates further refinement of these constraints with upcoming gravitational wave and electromagnetic observations, suggesting that future detections and analyses could narrow the discussed bounds further. This paves the way for addressing unresolved questions, such as the nature of phase transitions within neutron star cores and the presence of exotic matter like quark matter.

In conclusion, this paper exemplifies the synergy between observational advancements and theoretical modeling, marking progress in delineating the elusive properties of matter at supra-nuclear densities. As gravitational wave astronomy matures, its contributions to nuclear astrophysics and dense matter physics through such rigorous studies will undoubtedly become increasingly significant.