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

Abstract

Despite their long history and astrophysical importance, some of the key properties of neutron stars are still uncertain. The extreme conditions encountered in their interiors, involving matter of uncertain composition at extreme density and isospin asymmetry, uniquely determine the stars' macroscopic properties within General Relativity. Astrophysical constraints on those macroscopic properties, such as neutron star masses and radii, have long been used to understand the microscopic properties of the matter that forms them. In this article we discuss another astrophysically observable macroscopic property of neutron stars that can be used to study their interiors: their tidal deformation. Neutron stars, much like any other extended object with structure, are tidally deformed when under the influence of an external tidal field. In the context of coalescences of neutron stars observed through their gravitational wave emission, this deformation, quantified through a parameter termed the tidal deformability, can be measured. We discuss the role of the tidal deformability in observations of coalescing neutron stars with gravitational waves and how it can be used to probe the internal structure of Nature's most compact matter objects. Perhaps inevitably, a large portion of the discussion will be dictated by GW170817, the most informative confirmed detection of a binary neutron star coalescence with gravitational waves as of the time of writing.

Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

“…Recent measurements of the neutron skin thickness of 208 Pb suggest a stiff EoS for densities ≲ρ nuc [16,17], though uncertainties are still large and there is potential tension with other laboratory probes [16,18,20]. Gravitational wave (GW) observations by LIGO [21] and Virgo [22] provide information about the tidal properties of merging NSs [23][24][25], and have thus far set an upper limit on the stiffness at ∼2 ρ nuc . However, they are intrinsically less informative for larger NS masses.…”

“…We infer that c 2 s reaches a maximum of 0.75 þ0. 25 −0.24 at a density of 1.01 þ6.3 −5.3 × 10 14 g=cm 3 (3.60 þ2. 25 −1.89 ρ nuc ) in NS matter.…”

“…25 −0.24 at a density of 1.01 þ6.3 −5.3 × 10 14 g=cm 3 (3.60 þ2. 25 −1.89 ρ nuc ) in NS matter. Our results are comparable to other analyses of the new J0740 þ 6620 radius measurement.…”

Progress in Constraining Nuclear Symmetry Energy Using Neutron Star Observables Since GW170817

“…Understanding the nature and constrain the Equation of State (EOS) of dense neutronrich nuclear matter is a major science goal [1][2][3][4] shared by many other astrophysical observations (see, e.g., the analyses and reviews in [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]) and terrestrial nuclear experiments (see, e.g., [22][23][24][25][26][27][28][29][30][31][32][33]). However, realizing this goal is very challenging for many scientific and technical reasons.…”

Leading nonlinear tidal effects and scattering amplitudes

“…In this paper we investigate the effects of tidal deformations [93][94][95] on the conservative two-body Hamiltonian during the inspiral phase, focusing on their structure in the post-Minkowskian expansion. The tidal deformations offer a window into the equation of state of neutrons stars [96][97][98][99] and test our understanding of black holes [83,[100][101][102][103][104][105][106][107] and of possible exotic physics [108][109][110][111][112][113][114].…”