Tidal Deformabilities and Radii of Neutron Stars from the Observation of GW170817 (1804.08583v4)

Abstract: We use gravitational-wave observations of the binary neutron star merger GW170817 to explore the tidal deformabilities and radii of neutron stars. We perform Bayesian parameter estimation with the source location and distance informed by electromagnetic observations. We also assume that the two stars have the same equation of state; we demonstrate that for stars with masses comparable to the component masses of GW170817, this is effectively implemented by assuming that the stars' dimensionless tidal deformabilities are determined by the binary's mass ratio $q$ by $\Lambda_1/\Lambda_2 = q^6$. We investigate different choices of prior on the component masses of the neutron stars. We find that the tidal deformability and 90$\%$ credible interval is $\tilde{\Lambda}=222^{+420}_{-138}$ for a uniform component mass prior, $\tilde{\Lambda}=245^{+453}_{-151}$ for a component mass prior informed by radio observations of Galactic double neutron stars, and $\tilde{\Lambda}=233^{+448}_{-144}$ for a component mass prior informed by radio pulsars. We find a robust measurement of the common areal radius of the neutron stars across all mass priors of $8.9 \le \hat{R} \le 13.2$ km, with a mean value of $\langle \hat{R} \rangle = 10.8$ km. Our results are the first measurement of tidal deformability with a physical constraint on the star's equation of state and place the first lower bounds on the deformability and areal radii of neutron stars using gravitational waves.

Analysis of Tidal Deformabilities and Radii of Neutron Stars from GW170817 Observations

The paper "Tidal Deformabilities and Radii of Neutron Stars from the Observation of GW170817" explores the properties of neutron stars by analyzing the gravitational-wave (GW) data from the binary neutron star merger GW170817. This paper leverages the tidal deformability parameter, a crucial aspect of understanding the equation of state (EOS) of dense matter, to infer neutron star properties.

Methodology and Key Findings

The authors employ Bayesian parameter estimation techniques incorporating information from both gravitational and electromagnetic observations. The primary goal is to deduce the dimensionless tidal deformabilities ($\Lambda_1, \Lambda_2$) and areal radii ($R_1, R_2$) of the neutron stars involved in GW170817. This estimation assumes a common EOS for both stars, effectively linking $\Lambda_1/\Lambda_2$ to the mass ratio $q$ using $\Lambda_1/\Lambda_2 = q^6$. The analysis examines different priors for the component masses: uniform distribution, constraints informed by double neutron star binaries, and data from radio pulsars.

Tidal Deformability and Radius Estimates:

• For a uniform component mass prior, the estimated tidal deformability is $\tilde{\Lambda}=222^{+420}_{-138}$.
• The analysis provides a 90% credible interval for the common areal radius of the neutron stars as $8.9 \le \hat{R} \le 13.2$ km, with a mean radius of $\langle \hat{R} \rangle = 10.8$ km.

These measurements are notable as they represent the first constraints on neutron star tidal deformability and radius directly derived from GW observations, including considerations of physical constraints on the EOS.

Implications and Discussion

The results have significant implications for our understanding of dense matter physics. The tight constraints on the radii and tidal deformability reinforce certain nuclear physics models. While these observations don't strongly favor any specific EOS over others, they do exclude some EOS models with extreme properties and suggest relatively moderate radii for neutron stars.

The paper's approach underscores the utility of multimodal astronomical observations in refining EOS models. The combination of GW data with electromagnetic observations allows researchers to better isolate and measure neutron star characteristics, ultimately enhancing the fidelity of the EOS models that describe the state's high-density asymptotic behavior.

Prospects for Future Research

Future advancements in technology will likely refine these measurements. Enhanced sensitivity in GW detectors would improve parameter estimation accuracy, particularly for $\tilde{\Lambda}$ and $R$. Additionally, accumulating observations from successive binary neutron star mergers would lead to more robust statistical analysis, reducing uncertainty in EOS constraints.

Given these constraints on neutron star modeling, the paper provides a foundation for future theoretical and observational efforts. It will be essential to cross-verify findings with neutron star models derived from other astrophysical observations, such as x-ray and radio pulsar data, to consolidate our overall understanding of neutron star matter.

In conclusion, this paper successfully utilizes GW data to extract crucial physical characteristics of neutron stars, laying a foundational understanding of their structure and opening avenues for further detailed astrophysical and theoretical investigations.