Exploring the effective tidal deformability of neutron stars

Abstract

Finite size effects come into play during the late stages of neutron star binary inspiral, with the tidal deformability of the supranuclear density matter leaving an imprint on the gravitational-wave signal. As demonstrated in the case of GW170817, this leads to a constraint on the neutron star radius (and hence the equation of state). A deeper understanding of the tidal response requires an analysis of both the state and composition of matter. While these aspects may not have dramatic impact, they could lead to systematic effects that need to be kept in mind as the observational data become more precise. As a step in this direction we explore the role of the composition of matter, which is likely to remain "frozen" during the late stages of binary inspiral. We provide the first in-depth analysis of the problem, including estimates of how composition impacts on the effective tidal deformability. The results provide improved insight into how aspects of physics that tend to be "ignored" impact on binary neutron star gravitational-wave signals.

Gravitational-wave asteroseismology with fundamental modes from compact binary inspirals

“…Among these modes, the fundamental (f ℓ -)modes have the strongest tidal coupling and lead to a f-mode frequency-dependent amplification of tidal signatures in the GW signal that starts to accumulate long before the resonance [3][4][5] . In General Relativity (GR), and for a range of proposed nuclear EoSs for NSs, the f ℓ -mode frequencies are empirically found to be related to Λ ℓ through approximate universal relations (URs) 6,7 . However, not imposing such URs opens up the possibility of using GW observations to perform parameterised tests of GR, to understand properties of matter at supranuclear densities such as possible phase transitions from hadronic to quark matter 8 , and to test for the existence of exotic compact objects such as boson stars or gravastars 9 .…”

A gravitational-wave perspective on neutron-star seismology

“…In general, the mode-sum allows us to quantify the level at which the matter composition enters the problem. Evidence for simple model problems (with a fixed value for Γ 1 providing the stratification) shows that the f-modes vastly dominate the tidal response, with p-and g-modes contributing at (most at) the few percent level [69]. This is an interesting observation given that third generation (3G) gravitational-wave detectors like the Einstein Telescope or the Cosmic Explorer may be able to constrain the tidal deformability to the few percent level [73].…”

“…The relation is exact for the constant density model, where we only have to consider the f-mode. We then get [69]…”

Modelling neutron star mountains

“…The first example we consider is motivated by tidal deformations [see, e.g., Andersson & Pnigouras (2020)]. The source potential is taken to be a solution of Laplace's equation,…”