Explore the vast range of titles available.

In this work, we investigate the structure and properties of neutron stars in R2 gravity using two approaches, viz: the perturbative and non-perturbative methods. For this purpose, we consider NS with several nucleonic, as well as strange EoS generated in the framework of relativistic mean field models. The strange particles in the core of NS are in the form of Λ hyperons and quarks, in addition to the nucleons and leptons. In both the approaches, we obtain mass–radius relation for a wide range of values of the extra degree of freedom parameter a arising due to modification of gravity at large scales. The mass–radius relation of the chosen equation of states lies well within the observational limit in the case of GR. We identify the changes in the property of neutron star in the background of f(R) gravity, and compare the results in both the methods. We also identify the best suited method to study the modified gravity using the astrophysical observations.

In the present work, we investigate the r-mode instability windows, spindown, and spindown rates of sub- and super-Chandrasekhar magnetized white dwarfs in the presence of Landau quantization of the electron gas and magnetic braking. The gravitational wave strain amplitudes due to r-mode instability is also calculated. The dominant damping mechanism is taken to be the shear viscosity arising due to scattering of the degenerate electrons from the ion liquid. We find that the critical frequencies of Landau-quantized magnetized white dwarfs are the lowest, those of non-Landau-quantized ones are higher, and those of non-magnetized ones are the highest at the same temperature. This implies that magnetic braking and Landau quantization both enhance r-mode instability. We have also seen that there is rapid spindown of magnetized white dwarfs due to additional magnetic braking term, but there is no considerable effect of Landau quantization on the spindown and spindown rates for magnetic field strengths relevant for white dwarf interiors. We find that the r-mode gravitational wave strain amplitude for a rapidly rotating super-Chandrasekhar white dwarf at 1 kpc is ∼ 10 - 27 , making isolated massive rapidly rotating hot magnetized white dwarfs prime candidates for search of gravitational waves in the future.

A phase transition from hadronic to exotic phases might occur in the early post-bounce phase of a core collapse supernova. We investigate the role of strange hyperons in the dynamical collapse of a non-rotating massive star to a black hole using 1D General relativistic simulation GR1D. We follow the dynamical formation and collapse of a protoneutron star (PNS) from the gravitational collapse of a 40Msolar progenitor of Wooseley, adopting Shen hyperonic EoS. We also study the neutrino signals that may be used as a probe to core collapse supernova. We compare the results with those of Shen nuclear EoS and understand the role of strange hyperons in the core collapse.

We study cold as well as hot neutron star (NS) at finite entropy using density dependent relativistic mean field model in the presence of nucleons and antikaon condensates. The parameters like gravitational mass(M), radius(R), moment of inertia(I) and quadrupole moment(Q) are calculated as a function of rotation frequency for a NS with fixed baryonic mass. Next, we investigate the relation of normalized I with compactness (M/R). Finally, we extend our study to calculate the tidal deformability parameter and tidal love number and show their variation with compactness.

We investigate the combined evolution of the dipolar surface magnetic field (B s ) and the spin-period (P s ) of known Magnetars and high magnetic field ( $${{\\rm{B}}_s} \\mathbin{\\lower.3ex\\hbox{$\\buildrel>\\over {\\smash{\\scriptstyle\\sim}\\vphantom{_x}}$}} {10^{13}}{\\rm{G}}$$ ) radio pulsars. We study the long term behaviour of these objects assuming a simple Ohmic dissipation of the magnetic field. Identifying the regions (in the P s -B s plane) in which these neutron stars would likely move into, before crossing the death-line to enter the pulsar graveyard, we comment upon the possible connection between the Magnetars and other classes of neutron stars.

It is an exceptionally opportune time for astrophysics when a number of next-generation mega-instruments are poised to observe the Universe across the entire electromagnetic spectrum with unprecedented data quality. The Square Kilometre Array (SKA) is undoubtedly one of the major components of this scenario. In particular, the SKA is expected to discover tens of thousands of new neutron stars giving a major fillip to a wide range of scientific investigations. India has a sizeable community of scientists working on different aspects of neutron star physics with immediate access to both the uGMRT (an SKA pathfinder) and the recently launched X-ray observatory Astrosat. The current interests of the community largely centre around studies of (a) the generation of neutron stars and the SNe connection, (b) the neutron star population and evolutionary pathways, (c) the evolution of neutron stars in binaries and the magnetic fields, (d) the neutron star equation of state, (e) the radio pulsar emission mechanism, and (f) the radio pulsars as probes of gravitational physics. Most of these studies are the main goals of the SKA first phase, which is likely to be operational in the next four years. This article summarizes the science goals of the Indian neutron star community in the SKA era, with significant focus on coordinated efforts among the SKA and other existing/upcoming instruments.

We perform a comparative Bayesian analysis of fermionic and bosonic dark matter admixed neutron stars (DMANS) by incorporating a comprehensive set of theoretical, experimental, and astrophysical constraints. The hadronic matter equation of state (EoS) is modeled using a relativistic mean-field approach, constrained by chiral effective field theory (\\(\\chi\\)EFT) calculations at low densities, finite nuclei and heavy-ion collision data at intermediate densities, and neutron star (NS) observations at high densities. For the dark sector, we consider fermionic dark matter (FDM) interacting via a dark vector meson, and two bosonic dark matter models (BDM1 and BDM2) characterized by self-interacting scalar fields. Bayesian inference is employed to constrain the model parameters, including the dark matter mass, coupling strength, and dark matter fraction within NSs. Our analysis finds that all models yield consistent nuclear matter parameters, allowing a small dark matter fraction under 10%. The presence of dark matter slightly softens the EoS, leading to a modest reduction in NS mass, radius, and tidal deformability, though all models remain compatible with NICER and GW170817 observations. The log-evidence and likelihood analyses reveal no statistical preference among the FDM and BDM models, indicating that current astrophysical data cannot decisively distinguish between fermionic and bosonic dark matter scenarios. This study provides a unified statistical framework to constrain dark matter properties using NS observables.

We studied the properties of dark matter admixed-neutron stars (DMANS), considering fermionic dark matter (DM) that interacts gravitationally with hadronic matter (HM). Using relativistic mean-field equations of state (EoSs) for both components, we solved the two-fluid Tolman Oppenheimer Volkoff (TOV) equations to determine neutron star (NS) properties assuming that DM is confined within the stellar core. For hadronic matter, we employed realistic EoSs derived from low energy nuclear physics experiments, heavy-ion collision data, and NS observations. To constrain key dark matter parameters such as particle mass, mass fraction, and the coupling to mass ratio, we applied Bayesian inference, incorporating various astrophysical data including mass, radii, and NICER mass-radius distributions for PSR J0740+6620 and PSR J0030+0451. Additionally, we explored the influence of high-density HM EoSs and examined the impact of stiffer hadronic EoSs, excluding the vector meson self-interaction term. Our findings indicate that current astrophysical observations primarily constrain the dark matter fraction, while providing limited constraints on the particle mass or coupling. However, the dark matter fraction is largely insensitive to how astrophysical observations or uncertainties in the high-density EoS are incorporated. Instead, it is predominantly determined by the stiffness of the hadronic EoS at high densities, with stiffer hadronic EoSs yielding a higher dark matter mass fraction. Therefore, we conclude that the dark matter fraction plays a crucial role in shaping the properties of DMANS. Future investigations incorporating more realistic EoSs and astrophysical observations of other compact objects may provide deeper insights into dark matter.

In recent years, modified gravity theories have gained significant attention as potential replacements for the general theory of relativity. Neutron stars, which are dense compact objects, provide ideal astrophysical laboratories for testing these theories. However, understanding the properties of neutron stars within the framework of modified gravity theories requires careful consideration of the presently known uncertainty of equations of state (EoS) that describe the behavior of matter at extreme densities. In this study, we investigate three realistic EoS generated using a relativistic mean field framework, which covers the currently known uncertainties in the stiffness of neutron star matter. We then employ a Bayesian approach to statistically analyze the posterior distribution of the free parameter \\(\\) of the \\(f(R)\\) gravity model, specifically \\(f(R) = R + R^2\\). By using this approach, we are able to account for our limited understanding of the interiors of neutron stars as well as the uncertainties associated with the modified gravity theory. We impose observational constraints on our analysis, including the maximum mass, and the radius of a neutron star with a mass of \\(1.4 M_\\) and \\(2.08 M_\\), which are obtained from X-ray NICER observations. By considering these constraints, we are able to robustly investigate the relationship between the \\(f(R)\\) gravity model parameter \\(\\) and the maximum mass of neutron stars. Our results reveal a universality relationship between the \\(f(R)\\) gravity model parameter \\(\\) and the maximum mass of neutron stars. This relationship provides insights into the behavior of neutron stars in modified gravity theories and helps us understand the degeneracies arising from our current limited knowledge of the interiors of neutron stars and the free parameter \\(\\) of the modified gravity theory.

Antikaon (\\(K^-\\)) condensation within neutron star matter (NS) depends on the antikaon-nucleon interaction potential (\\(U_K\\)). Appearance of \\(K^-\\) generally softens the equation of state (EOS). The impact of this softening on the structure of the NS can be leveraged to find a telltale sign of the phase transition from nucleonic matter to \\(K^-\\) condensation. To investigate the impact of \\(K^-\\) condensation on NS properties using a Bayesian inference framework, we choose two sets of RMF model parameters to obtain a stiff (DD2) and relatively soft (FSU) nucleonic EOS, and explore a wide range of optical potential depths. Multimessenger observations from NICER and LIGO/Virgo constrain the optical potential values to \\(U_K = -104.72^{+13.82}_{-12.48}\\) MeV and \\(U_K = -66.46^{+2.47}_{-3.42}\\) MeV for the stiff and soft cases, respectively. Deeper \\(K^-\\) potentials trigger condensation at a lower density, softening the EOS and lowering the corresponding maximum masses. While slopes of mass-radius and tidal deformability curves overlap between nucleonic and exotic EOSs, their curvature and \\(f-\\)mode oscillation properties (frequency and damping time) reveal features attributable to EOS softening. However, distinguishing the specific exotic degrees of freedom responsible for the softening remains an open challenge.