Empirical constraints on the high-density equation of state from multimessenger observables

Abstract

We search for possible correlations between neutron star observables and thermodynamic quantities that characterize high density nuclear matter. We generate a set of model-independent equations of state describing stellar matter from a Taylor expansion around saturation density. Each equation of state which is a functional of the nuclear matter parameters is thermodynamically consistent, causal and compatible with astrophysical observations. We find that the neutron star tidal deformability and radius are strongly correlated with the pressure, the energy density and the sound velocity at different densities. Similar correlations are also exhibited by a large set of mean-field models based on non-relativistic and relativistic nuclear energy density functionals. These model independent correlations can be employed to constrain the equation of state at different densities above saturation from measurements of NS properties with multi-messenger observations. In particular, precise constraints on the radius of PSR J0030+0451 thanks to NICER observations would allow to better infer the properties of matter around two times the nuclear saturation density.

Nonparametric constraints on neutron star matter with existing and upcoming gravitational wave and pulsar observations

“…greater model freedom allowed by our nonparametric representation of the EoS, we are not able to rule out any phase transition phenomenology based on the joint astronomical observations, although the connections between the constraints on macroscopic EoS observables and the nuclear microphysics merit further investigation (see e.g., [138,139]). Conversely, nuclear theory predictions, e.g., from chiral effective field theory [140][141][142][143], are known to be helpful in constraining the low-density EoS [52,144,145].…”

Neutron-star tidal deformability and equation-of-state constraints

“…Various studies have empirically identified correlations between various combinations of parameters that characterize the symmetry energy and its density dependence with the neutron star radius and tidal parameters [246,[266][267][268][269] or terrestrial experimental results [239,[270][271][272], as they all are linked to the low-density behavior of the equation of state around (twice) saturation. The tidal constraints from GW170817, and more recently radius constraints from NICER have been used to examine implications for the symmetry energy [273][274][275][276][277][278][279][280][281][282] as well as potential systematics in the mapping [283].…”

Interpreting binary neutron star mergers: describing the binary neutron star dynamics, modelling gravitational waveforms, and analyzing detections

“…This is valid for any and (44) is to be substituted for y when evaluating Λ from (42). A number of studies have computed examples of Λ for a wide range of EOS models and delineated interpretations of its physics content such as symmetry energy, phase transitions, and multi-body interactions [16,25,29,30,59,74,86,112,113,121,129,168,[204][205][206]213,223,239,246,254,267,270,282,293,305,307,319,328,329,[343][344][345][346][347][348][349][350][351][353][354][355]362,363,365,378,385,402,…”