Tidal Deformability Of Neutron Stars Research Articles

Exploring the Distribution and Impact of Bosonic Dark Matter in Neutron Stars

The presence of dark matter (DM) within neutron stars (NSs) can be introduced by different accumulation scenarios in which DM and baryonic matter (BM) may interact only through the gravitational force. In this work, we consider asymmetric self-interacting bosonic DM, which can reside as a dense core inside the NS or form an extended halo around it. It is seen that depending on the boson mass (mχ), self-coupling constant (λ) and DM fraction (Fχ), the maximum mass, radius and tidal deformability of NSs with DM admixture will be altered significantly. The impact of DM causes some modifications in the observable features induced solely by the BM component. Here, we focus on the widely used nuclear matter equation of state (EoS) called DD2 for describing NS matter. We show that by involving DM in NSs, the corresponding observational parameters will be changed to be consistent with the latest multi-messenger observations of NSs. It is seen that for mχ≳200 MeV and λ≲2π, DM-admixed NSs with 4%≲Fχ≲20% are consistent with the maximum mass and tidal deformability constraints.

Impact of Fermi-surface distortion in a relativistic mean-field model on the moment of inertia and tidal deformability of neutron stars

Impact of Fermi-surface distortion in a relativistic mean-field model on the moment of inertia and tidal deformability of neutron stars

Tidal Deformability of Neutron Stars in Scalar-tensor Theories of Gravity

Gravitational waves from compact binary coalescences are valuable for testing theories of gravity in the strong field regime. By measuring neutron star tidal deformability using gravitational waves from binary neutron stars, stringent constraints were placed on the equation of state of matter at extreme densities. Tidal Love numbers in alternative theories of gravity may differ significantly from their general relativistic counterparts. Understanding exactly how the tidal Love numbers change will enable scientists to untangle physics beyond general relativity from the uncertainty in the equation of state measurement. In this work, we explicitly calculate the fully relativistic l ≥ 2 tidal Love numbers for neutron stars in scalar-tensor theories of gravitation. We use several realistic equations of state to explore how the mass, radius, and tidal deformability relations differ from those of general relativity. We find that tidal Love numbers and tidal deformabilities can differ significantly from those in general relativity in certain regimes. The electric tidal deformability can differ by ∼200%, and the magnetic tidal deformability differs by ∼300%. These deviations occur at large compactnesses (C = M/r ≳ 0.2) and vary slightly depending on the equation of state. This difference suggests that using the tidal Love numbers from general relativity could lead to significant errors in tests of general relativity using the gravitational waves from binary neutron star and neutron star black hole mergers.

What constraints can one pose on the maximum mass of neutron stars from multimessenger observations?

ABSTRACT The maximum mass of neutron stars (MTOV) plays a crucial role in understanding their equation of state (EoS). Previous studies have used the measurements for the compactness of massive pulsars and the tidal deformability of neutron stars in binary neutron star (BNS) mergers to constrain the EoS and thus the MTOV. The discovery of the most massive pulsar, PSR J0952−0607, with a mass $\sim 2.35\, {\rm M}_{\odot }$, has provided a valuable lower limit for MTOV. Another efficient method to constrain MTOV is by examining the type of central remnant formed after a BNS merger. Gravitational wave (GW) data can provide the total mass of the system, while accompanying electromagnetic signals can help infer the remnant type. In this study, we combine all the previous constraints and utilize the observational facts that about 24 per cent of the short gamma-ray bursts are followed by an X-ray internal plateau, which indicate that roughly this fraction of BNS mergers yield supermassive neutron stars, to perform (Markov Chain) Monte Carlo simulations. These simulations allow us to explore the probability density distribution of MTOV and other parameters related to BNS mergers. Our findings suggest that MTOV is likely around $2.49\!-\!2.52\, {\rm M}_{\odot }$, with an uncertainty range of approximately [$-0.16$, $0.15\, {\rm M}_{\odot }$] ([$-0.28$, $0.26\, {\rm M}_{\odot }$]) at 1σ (2σ) confidence level. Furthermore, we examine the type of merger remnants in specific events like GW170817 and GW190425 to further constrain MTOV and other relevant parameters, which can help to understand the physical processes involved in BNS mergers.

The role of temperature on the tidal deformability of an inspiraling binary neutron star system

The detection of gravitational waves emitted by binary neutron star mergers consists a very promising tool for studying the properties of dense nuclear matter. The lack of exact evidence for a zero-temperature scenario regarding the inspiral phase of a coalescing binary neutron star system raises the question of the role of temperature. Based on some theoretical studies, the existence of temperature (about a few MeV) before the merger is possible. The main goal of our work is to study the thermal effects on the tidal deformability of neutron stars, by taking into consideration the observations of binary neutron star mergers. In our study, we used various hot equations of state, both isothermal and adiabatic, and for different nuclear models. The main finding is that for temperature below 1 MeV the tidal deformability as a function of the neutron star mass remains insensible. In the adiabatic case, this behavior is present up to entropy per baryon S=0.2 kB.

Systematic errors due to quasiuniversal relations in binary neutron stars and their correction for unbiased model selection

Inference of the equation of state (EOS) of dense nuclear matter in neutron-star cores is a principal science goal of x-ray and gravitational-wave observations of neutron stars. In particular, gravitational-wave observations provide an independent probe of the properties of bulk matter in neutron star cores that can then be used to compare with theoretically derived equations of state. In this paper, we quantify the systematic errors arising from the application of EOS-independent quasiuniversal relations in the estimation of neutron star tidal deformabilities and radii from gravitational-wave measurements and introduce a strategy to correct for the systematic biases in the inferred radii. We apply this method to a simulated population of events expected to be observed by future upgrades of current detectors and the next generation of ground-based observatories. We show that our approach can accurately correct for the systematic biases arising from approximate universal relations in the mass-radius curves of neutron stars. Using the posterior distributions of the mass and radius for the simulated population we infer the underlying EOS with a good degree of precision. Our method revives the possibility of using the universal relations for rapid Bayesian model selection of the dense matter EOS in gravitational-wave observations.

Tidal Deformability of Neutron Stars in Unimodular Gravity

Unimodular gravity is a modified theory with respect to general relativity by an extra condition that the determinant of the metric is fixed. Especially, if the energy-momentum tensor is not imposed to be conserved separately, a new geometric structure will appear with potential observational signatures. In this paper, we study the tidal deformability of a compact star in unimodular gravity under the assumption of a non-conserved energy-momentum tensor. Both the electric-type and magnetic-type quadrupole tidal Love numbers are calculated for neutron stars using the polytrope model. It is found that the electric-type tidal Love numbers are monotonically increasing, but the magnetic-type ones are decreasing, with the increase in the non-conservation parameter. Compared with the observational data from the detected gravitational-wave events, a small negative non-conservation parameter is favored.

Measurability of neutron star tidal deformability from merging neutron star-black hole binaries

The neutron star-black hole binary (NSBH) system has been considered one of the promising detection candidates for ground-based gravitational-wave (GW) detectors such as LIGO and Virgo. The tidal effects of neutron stars (NSs) are imprinted on the GW signals emitted from NSBHs as well as binary neutron stars. In this work, we study how accurately the parameter $\lambda_{\rm NS}$ can be measured in GW parameter estimation for NSBH signals. We set the parameter range for the NSBH sources to $[4M_{\odot}, 10M_{\odot}]$ for the black hole mass, $[1M_{\odot}, 2M_{\odot}]$ for the NS mass, and $[-0.9, 0.9]$ for the dimensionless black hole spin. For realistic populations of sources distributed in different parameter spaces, we calculate the measurement errors of $\lambda_{\rm NS}$ ($\sigma_{\lambda_{\rm NS}}$) using the Fisher matrix method. In particular, we perform a single-detector analysis using the advanced LIGO and the Cosmic Explorer detectors and a multi-detector analysis using the 2G (advanced LIGO-Hanford, advanced LIGO-Livingstone, advanced Virgo, and KAGRA) and the 3G (Einstein Telescope and Cosmic Explorer) networks. We show the distribution of $\sigma_{\lambda_{\rm NS}}$ for the population of sources as a one-dimensional probability density function. Our result shows that the probability density function curves are similar in shape between advanced LIGO and Cosmic Explorer, but Cosmic Explorer can achieve $\sim 15$ times better accuracy overall in the measurement of $\lambda_{\rm NS}$. In the case of the network detectors, the probability density functions are maximum at $\sigma_{\lambda_{\rm NS}} \sim 130$ and $\sim 4$ for the 2G and the 3G networks, respectively, and the 3G network can achieve $\sim 10$ times better accuracy overall.

Dependence of the tidal deformability of neutron stars on the nuclear equation of state* *Supported by the Shanxi Provincial Foundation for Returned Overseas Scholars (20220037), the Natural Science Foundation of Shanxi Province (20210302123085), the discipline construction project of Yuncheng university, and the National Natural Science Foundation of China (12075327)

Within the Bayesian framework, using an explicitly isospin-dependent parametric equation of state (EOS) for the core of neutron stars (NSs), we studied how the NS EOS behaves when we confront it with the tidal deformabilities of canonical NSs with different error and different lower boundaries, and with the tidal deformabilities of massive NSs. We found that it does not significantly improve the constraints on the NS EOS but has a weak effect on narrowing down the slope parameter of the symmetry energy by decreasing the measurement errors of . Both the isospin-dependent and isospin-independent parts of the NS EOS were significantly constrained and raised as the tidal deformabilities of massive NSs were adopted in the calculations, especially in high-density regions. We also found that is more competent to limit the curvature parameter than the slope parameter of the symmetry energy, whereas the opposite occurs for the radius of canonical NSs . The tidal deformability of an NS with two times the solar mass is more sensitive to skewness than the curvature parameter of the symmetry energy, and and have no correlation with the former.

Thermal effects on tidal deformability in the last orbits of an inspiraling binary neutron star system

The study of binary neutron stars mergers by the detection of the emitted gravitational waves is one of the most promised tools to study the properties of dense nuclear matter at high densities. It is worth claiming that strong evidence that the temperature of the stars during the last orbits before coalescing is very low, T≪1 MeV (hereafter cold case or cold star; kB=1), does not exist. Nevertheless, theoretical studies suggest that the temperature concerning the inspiral phase, could reach even a few MeV. The heating process of the interior of the neutron stars is as follows; tides transfer mechanical energy and angular momentum to the star at the expense of the orbit, where friction within the star converts the mechanical energy into heat. During the inspiral, these effects are potentially detectable. Different treatments have been used to estimate the transfer of the mechanical energy and the size of the tidal friction, leading to different conclusions about the importance of pre-merger tidal effects. The present work is dedicated to the study of the effect of temperature on the tidal deformability of neutron stars during the inspiral of a neutron star system just before the merger. We applied a class of hot equations of state, both isothermal and adiabatic, originated from various nuclear models. We found that even for low values of temperature (T<1 MeV), the effects on the basic ingredients of tidal deformability are not negligible. On the other hand, in the case of the adiabatic star, the thermal effects on tidal deformability remain imperceptible, up to the entropy per baryon value S=0.2 (in units of kB). According to the main finding, the effects of the temperature on tidal deformability, at least for low temperatures, are almost negligible. This is a surprising effect since both radius and Love number, the basic ingredients of the tidal deformability, are sensitive to temperature. The consequences of the above result are discussed and analyzed.

Spin symmetry energy and equation of state of spin-polarized neutron star matter

The equation of state (EOS) of spin-polarized nuclear matter (NM) is studied within the Hartree-Fock (HF) formalism using the realistic density-dependent nucleon-nucleon interaction. With a nonzero fraction $\mathrm{\ensuremath{\Delta}}$ of spin-polarized baryons in NM, the spin- and spin-isospin dependent parts of the HF energy density give rise to the spin symmetry energy that behaves in about the same manner as the isospin symmetry energy, widely discussed in the literature as the nuclear symmetry energy. The present HF study shows a strong correlation between the spin symmetry energy and nuclear symmetry energy over the whole range of baryon densities. The important contribution of the spin symmetry energy to the EOS of the spin-polarized NM is found to be comparable with that of the nuclear symmetry energy to the EOS of the isospin-polarized or asymmetric (neutron-rich) NM. Based on the HF energy density, the EOS of the spin-polarized ($\ensuremath{\beta}$-stable) $npe\ensuremath{\mu}$ matter is obtained for the determination of the macroscopic properties of neutron stars (NS). A realistic density dependence of the spin-polarized fraction $\mathrm{\ensuremath{\Delta}}$ has been suggested to explore the impact of the spin symmetry energy on the gravitational mass $M$ and radius $R$, as well as the tidal deformability of NS. Based on the empirical constrains inferred from a coherent Bayesian analysis of gravitational wave signals of the NS merger GW170817 and the observed masses of the heaviest pulsars, the present study shows the strong impact of the spin symmetry energy $W$, nuclear symmetry energy $S$, and nuclear incompressibility $K$ on the EOS of nucleonic matter in magnetar.

Neutron stars in massive scalar-Gauss-Bonnet gravity: Spherical structure and time-independent perturbations

The class of scalar-tensor theories with the scalar field coupling to the Gauss-Bonnet invariant has drawn great interest since solutions of spontaneous scalarization were found for black holes in these theories. We contribute to the existing literature a detailed study of the spontaneously scalarized neutron stars (NSs) in a typical theory where the coupling function of the scalar field takes the quadratic form and the scalar field is massive. The investigation here includes the spherical solutions of the NSs as well as their perturbative properties, namely the tidal deformability and the moment of inertia, treated in a unified and extendable way under the framework of spherical decomposition. We find that while the mass, the radius, and the moment of inertia of the spontaneously scalarized NSs show very moderate deviations from those of the NSs in general relativity (GR), the tidal deformability exhibits significant differences between the solutions in GR and the solutions of spontaneous scalarization for certain values of the parameters in the scalar-Gauss-Bonnet theory. As a result, the celebrated universal relation between the moment of inertia and the tidal deformability of neutron stars breaks down. With the mass and the tidal deformability of NSs attainable in the gravitational waves from binary NS mergers, the radius measurable using the X-ray satellites, and the moment of inertia accessible via the high-precision pulsar timing techniques, future multi-messenger observations can be contrasted with the theoretical results and provide us necessary information for building up theories beyond GR.

Early deconfinement of asymptotically conformal color-superconducting quark matter in neutron stars

We present a relativistic density functional approach to color superconducting quark matter that mimics quark confinement by a fast growth of the quasiparticle selfenergy in the confining region. The approach is shown to be equivalent to a chiral model of quark matter with medium dependent couplings. While the (pseudo)scalar sector of the model is fitted to the vacuum phenomenology of quantum chromodynamics, the strength of interaction in the vector and diquark channels is varied in order to provide the best agreement with the observational constraints on the mass-radius relation and tidal deformability of neutron stars modelled with our approach. In order to recover the conformal behavior of quark matter at asymptotically high densities we introduce a medium dependence of the vector and diquark couplings motivated by the non-perturbative gluon exchange. Our analysis signals that the onset of deconfinement to color superconducting quark matter is likely to occur in neutron stars with masses below 1.0 M⊙.

Inferring the dense nuclear matter equation of state with neutron star tides

During the late stages of a neutron star binary inspiral finite-size effects come into play, with the tidal deformability of the supranuclear density matter leaving an imprint on the gravitational-wave signal. As demonstrated in the case of GW170817—the first direct detection of gravitational waves from a neutron star binary—this can lead to strong constraints on the neutron star equation of state. As detectors become more sensitive, effects which may have a smaller influence on the neutron star tidal deformability need to be taken into consideration. Dynamical effects, such as oscillation mode resonances triggered by the orbital motion, have been shown to contribute to the tidal deformability, especially close to the neutron star coalesence, where current detectors are most sensitive. We calculate the contribution of the various stellar oscillation modes to the tidal deformability and demonstrate the (anticipated) dominance of the fundamental mode. We show what the impact of the matter composition is on the tidal deformability, as well as the changes induced by more realistic additions to the problem, e.g. the presence of an elastic crust. Finally, based on this formulation, we develop a simple phenomenological model describing the effective tidal deformability of neutron stars and show that it provides a surprisingly accurate representation of the dynamical tide close to merger.

Constraints on the Equation of State of Dense Nuclear Matter from the Tidal Deformability of Neutron Stars

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Tidal deformabilities of neutron stars in scalar-Gauss-Bonnet gravity and their applications to multimessenger tests of gravity

The spacetime surrounding compact objects such as neutron stars and black holes provides an excellent place to study gravity in the strong, nonlinear, dynamical regime. Here, the effects of strong curvature can leave their imprint on observables which we may use to study gravity. Recently, NICER provided a mass and radius measurement of an isolated neutron star using x-rays, while LIGO/Virgo measured the tidal deformability of neutron stars through gravitational waves. These measurements can be used to test the relation between the tidal deformability and compactness of neutron stars that are known to be universal in general relativity. Here, we take (shift-symmetric) scalar-Gauss-Bonnet gravity (motivated by a low-energy effective theory of a string theory) as an example and study whether one can apply the NICER and LIGO/Virgo measurements to the universal relation to test the theory. To do so, this paper is mostly devoted on theoretically constructing tidally deformed neutron star solutions in this theory perturbatively and calculate the tidal deformability for the first time. We find that the relation between the tidal deformability and compactness remains to be mostly universal for a fixed dimensionless coupling constant of the theory though the relation is different from the one in general relativity. We also present a universal relation between the tidal deformability of one neutron star and the compactness for another neutron star that can be directly applied to observations by LIGO/Virgo and NICER. For the equations of state considered in this paper, it is still inconclusive whether one can place a meaningful bounds on scalar Gauss-Bonnet gravity with the new universal relations. However, we found a new bound from the mass measurement of the pulsar $\mathrm{J}0740+6620$ that is comparable to other existing bounds from black hole observations.

Tidal Love numbers of neutron stars in Rastall gravity

Gravitational-wave measurements of the tidal deformability of neutron stars could reveal important information regarding their internal structure, the equation of state of high-dense nuclear matter and gravity in strong field regime. In this work, we extend the relativistic theory of the tidal deformability of neutron stars to Rastall gravity. Both the electric-type and magnetic-type quadrupole tidal Love numbers are calculated for neutron stars in the polytrope model. It is found that neutron star's tidal Love numbers in Rastall gravity is significantly smaller than those in general relativity. Our results provide new evidence of the degeneracy between the modification of gravity and the equation of state of nuclear matter in neutron stars.

Radius and equation of state constraints from massive neutron stars and GW190814

Motivated by the unknown nature of the $2.50-2.67\,M_\odot$ compact object in the binary merger event GW190814, we study the maximum neutron star mass based on constraints from low-energy nuclear physics, neutron star tidal deformabilities from GW170817, and simultaneous mass-radius measurements of PSR J0030+045 from NICER. Our prior distribution is based on a combination of nuclear modeling valid in the vicinity of normal nuclear densities together with the assumption of a maximally stiff equation of state at high densities, a choice that enables us to probe the connection between observed heavy neutron stars and the transition density at which conventional nuclear physics models must break down. We demonstrate that a modification of the highly uncertain supra-saturation density equation of state beyond 2.64 times normal nuclear density is required in order for chiral effective field theory models to be consistent with current neutron star observations and the existence of $2.6\,M_\odot$ neutron stars. We also show that the existence of very massive neutron stars strongly impacts the radii of $\sim 2.0\,M_\odot$ neutron stars (but not necessarily the radii of $1.4\,M_\odot$ neutron stars), which further motivates future NICER radius measurements of PSR J1614-2230 and PSR J0740+6620.

Neutron star deformability with hyperonization in density-dependent relativistic mean-field models

Neutron star tidal deformability extracted from gravitational wave data provides a novel probe to the interior neutron star structures and the associated nuclear equation of state (EOS). Instead of the popular composition of nucleons and leptons in neutron stars, we include hyperons and examine the role of hyperons in the tidal deformability and its impact on the symmetry energy in a relativistic mean-field approach with the density-dependent parametrizations. The hyperons are found to have a significant impact on the deformability, correlated sensitively with the onset density and fraction of hyperons in neutron star matter. A moderately lower onset density of hyperons can yield considerable modification to the tidal deformability and shift its inference on the nuclear EOS. The future measurements of the tidal deformability at multifiducial star masses are anticipated to lift the degeneracy between the contributions from the hyperon component and symmetry energy.

Tidal deformability of neutron stars with exotic particles within a density dependent relativistic mean field model in R-squared gravity

There is a growing interest in investigating modified theories of gravity, primarily, with the aim of explaining the universe's accelerated expansion, which has been confirmed by several independent observations. Compact objects, like neutron stars, exhibit strong gravity effects and therefore are used to study modified gravity theories. We use the f(R)=R+aR 2 model, where R is the Ricci scalar and a is a free parameter. This model has been studied both perturbatively and non-perturbatively. However, it was found that perturbative methods results in nonphysical solutions for the neutron stars. In this paper, we examine neutron star properties, such as mass, radius, tidal deformability in non-perturbative f(R) gravity model with density dependent relativistic equation of state with different particle compositions. The strange particles in the core of NS in the form of Λ hyperons, K - condensate, and quarks are considered. We have observed that while the mass-radius relation allows for a wide range of parameter a, when tidal deformability is considered, the parameter a is constrained down by one order.