Neutron stars were first posited in the early thirties, and discovered as pulsars in the late sixties; however we are only recently beginning to understand the matter they contain. I will describe the ongoing development of a consistent picture of the liquid interiors of neutron stars, now driven by ever increasing observations as well as theoretical advances. These include in particular...
Traditionally, neutron star observations from which mass and radius estimates are obtained are used to inform the dense matter equation of state through Bayesian inference. This procedure introduces a difficult-to-infer uncertainty stemming from prior choices for equation of state models and their parameters. We are developing a method to directly estimate central values of energy density...
Models of neutron and quark stars are considered in the case of a uniform density distribution. A universal
algebraic equation, valid for any equation of state, is obtained in General Relativity. This equation allows one to find
the approximate mass of a star for a given density without resorting to the integration of differential equations. The solutions neutron star models for various...
We perform a Bayesian analysis of the equation of state (EOS) constraints using recent observational data, including pulsar masses, radii, and tidal deformabilities. Our focus is on a class of hybrid neutron star EOS that incorporates color superconducting quark matter, based on a recently developed nonlocal chiral quark model. The nuclear matter phase is described using a relativistic density...
The equation of state (EoS) for dense, strongly interacting matter serves as the central input in an array of astrophysical simulations involving isolated compact objects and binary systems across various scenarios. While numerous models exist to describe the composition of cold neutron stars, the range narrows considerably when considering the so-called general-purpose EoS, which encompass...
By consideration of the Compact object HESS J1731-347 as a hybrid twin
compact star, i.e., a more compact star than its hadronic twin of the
same mass, its stellar properties are derived. Besides showing that the
properties of compact stars in this work are in good agreement with
state-of-the-art constraints both from measurements carried out in
laboratory experiments as well as by...
We investigate the correspondence between modified gravity theories and general entropic cosmology theory. Such a theory is proposed by an analogy with Jacobson’s work, where the Einstein equation was derived from the Bekenstein-Hawking entropy. We compare FLRW equations obtained in entropic gravity with those in modified gravity theories. It is found the correspondence of F(T) and F(Q)...
I will present an overview of the history of observing supermassive black holes (SMBHs) in contemporary astronomy, including discussing various methods to detect these objects, and constrain their masses and accretion rates. I will go on to review important evidence for SMBHs impacting their host galaxies via a mix of : (i) “quasar-mode”, ejective feedback; and via (ii) “radio-mode”,...
We revisit the derivation of the Rhoades-Ruffini bound [1] of 3.2 M⊙ for the upper limit of the maximum mass of neutron stars. We find that the assumption made there for the onset density of an ultimately stiff phase of high-density matter is not stringent. Relaxing this assumption and allowing for an onset of stiff non-nucleonic constant-speed-of-sound matter under neutron star constraints at...
The combined effects of spatial curvature and topology are investigated on the properties of the vacuum state for a charged scalar field localized on the (2+1)-dimensional Beltrami pseudosphere. It is assumed that the field obeys the quasiperiodicity condition along azimuthal angle with a constant phase. As important local characteristics of the vacuum state the vacuum expectation values...
Spherical orbits around rotating black holes have a major astrophysical importance. In the presence of quintessential matter [1, 2], the geodesic equations can be investigated using a combined numerical-analytical approach [3]. One may notice significant differences compared to the results previously derived for Kerr black holes [4]. Also, as it is known, the rotating black holes produce...
Observed cooling rate of the young neutron star (NS) in the Cassiopeia A supernova remnant (Cas A NS) exceeds theoretical expectations based on conventional scenarios of NS cooling, controlled mainly by modified Urca (mUrca) neutrino emission. Several hypotheses have been suggested to explain these observations. The most popular one assumes the cooling enhancement by neutrino emission due to...
One of the key challenges in the theory of neutron star cooling is to explain the observed existence of compact relativistic objects of the same age but with different surface temperatures. To address this issue, we investigate the dependence of the neutrino cooling rate on the average density, mass, and internal structure of a neutron star. This study focuses on the medium modification of...
Gaia detected a new population of neutron stars. They are the oldest neutron stars known, which are members of wide binaries with small orbital velocities. I argue that their current orbits are fossils of their turbulent youth and present considerable clues to the physics of their younger selves.
Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.
This work investigates the bulk viscosity of warm, dense,
neutrino-transparent, color-superconducting quark matter, where
damping of density oscillations in the kHz frequency range arises
from weak-interaction-driven direct Urca processes involving
quarks. We study the two-flavor red-green paired
color-superconducting (2SC) phase, while allowing for the presence
of unpaired strange...
Born from gravitational-core collapse supernovae, with initial temperatures as high as $\sim 10^{12}$K, neutron stars cool down to temperatures $10^9$ K within a few days, providing a unique opportunity to explore matter under extreme conditions. In particular, neutron stars contain nuclear superfluids whose presence is supported by observations of pulsar frequency glitches, rapid decline in...
The pseudo-Riemann metric organization of spacetime can describe the quasi-elastic field hierarchy with the constant rest energy integral in the case of negligible inelastic losses or non-metric intrusions. Visible matter consists of very dense regions of massive fields associated with the material analogue of the Einstein tensor. The non-Schwarzschild metric solution of the non-dual analogue...
Recently, within the framework of the stochastic Yang-Mills equations for the gauge symmetry group SU(2)xU(1), the possibility of the evidence of massless Bose particles with spin-1- The formation of a scalar field from an ensemble of chions as a result of Bose condensation of entangled pairs of chions with a common spin of 0 is theoretically substantiated. has been proven [1]. The formation...
ABSTRACT
Until now, the theory of quantum mechanics of the photon has not been sufficiently developed; moreover, the idea of the wave function of the photon is often considered a controversial concept, see, for example [1]. Note that for the photon, there is only the quantum theory of the electromagnetic radiation, which, except for the frequency or wavelength, does not provide any other...
The energy density functional for dense nuclear matter can be presented as the sum of two parts. The isospin-symmetric part determines the equation of state of symmetric nuclear matter. The isospin-asymmetric part is commonly considered to be proportional to the squared isospin asymmetry, with the proportionality coefficient referred to as the nuclear symmetry energy. There are two ways to...
This work investigates thermoelectric coefficients (electrical and thermal conductivities and thermoelectric power) of two-flavor quark matter from the Kubo formalism within the framework of the Nambu–Jona-Lasinio model. The subject of the study is quark matter under physical conditions relevant to heavy-ion collisions, where electric fields and temperature gradients are present...
We investigate the electrical conductivity of hot and dense plasma relevant to the outer crusts of neutron stars and the interiors of white dwarfs. The main novelty of the work is the inclusion of positrons in the composition of matter and in the transport. We solve a system of coupled Boltzmann kinetic equations for electrons' and positrons' distribution functions in the relaxation time...
We study the thermal conductivity and thermoelectric power of the inner crust of a neutron star at finite temperatures where ions are in a liquid state. Such crust can be formed in various astrophysical scenarios including binary neutron star mergers, proto-neutron stars and accreting neutron stars. We employed the linearized Boltzmann equation assuming simultaneous presence of...
We investigate the dynamics of test particles near a magnetized black hole surrounded by quintessence which is modeled as an anisotropic fluid with a specific equation of state [1,2]. The motion of both massive and massless test particles is analyzed using the Lagrangian formalism, with particular focus on the effective potential governing their trajectories. Quintessence modifies the...
The magnetic field strengths of neutron stars are typically inferred from pulse timing, relying on a model for the electromagnetic braking torque. I will provide a theoretical overview for the various pieces of physics that adjust this torque, relating to general-relativistic effects, the equation of state, magnetospheric conditions, and dynamical phenomena, arguing that actually there is a...
One of the important properties of nuclear forces is
the nuclear repulsive core which provides a stability for atomic nuclei, making
possible the emergence of a structure for the visible matter.
However the origin of the nuclear core is poorly understood. We discuss how
the strong repulsive nuclear core at short distances can emerge from QCD,
even though one should expect a...
The discrepancy between low and high redshift Hubble constant $H_0$ measurements is the highest significance tension within the concordance Lambda cold dark matter paradigm. If not due to unknown systematics, the Hubble Puzzle suggests a lack of understanding of the universe’s expansion history despite the otherwise spectacular success of the theory. We show that a Gödel inspired slowly...
R-modes are quasitoroidal oscillations of rotating stars, primarily restored by the Coriolis force. The fact that, among the variety of stellar oscillations, r-modes are the most susceptible to the Chandrasekhar-Friedman-Schutz (CFS) instability (i.e., instability with respect to gravitational wave emission) makes them promising targets for current and future gravitational wave searches. An...
We present the results of self-consistent radiation-hydrodynamic modeling of accretion channels of subcritical X-ray pulsars. The process of resonant Compton scattering and vacuum polarization is taken into account. It is shown that the radiation in the cyclotron line is determined by the hydrodynamic characteristics of the flow in the accretion channel and the position of the cyclotron line...
Some electromagnetic properties of the protoquark star matter are investigated. It is assumed that during the formation of the protoquark star, the matter of the initial star was already opaque for neutrinos. Thus, this process was accompanied by the conservation of the total lepton charge. The lepton charges of the protoquark star and the initial star are almost equal. In our numerical...
We study rotating hybrid stars, with a particular emphasis on the effect of a deconfinement phase
transition on their properties at high spin. Our analysis is based on a hybrid equation of state with
a phase transition from hypernuclear matter to color-superconducting quark matter, where both
phases are described within a relativistic density functional approach. By varying the vector...
Observed data about quasi-periodic variations of period derivative of pulsars is considered. Characteristic radii of superfluid regions of pulsars are derived under the assumption that these variations are collective elastic oscillations of the superfliud vortex lattice (Tkachenko oscillations). The found values of radii are compared with values derived from X-ray data NICER and XMM-Newton...
The presence of dark matter in neutron stars is of growing interest due to its possible impact on their structure and observables. Among proposed candidates, the hypothetical sexaquark has emerged as a promising bosonic dark matter particle, potentially forming under extreme conditions in neutron star cores.
We investigate this scenario using a relativistic density functional approach,...
This study explores the equations of state for strange quark matter as a superdense ground state within the MIT bag model, considering both fixed and baryon density–dependent parameters. We examine the structure of cold, self-bound strange stars capable of reaching masses above two solar masses, forming a continuous family with neutron stars along the mass–central density (M(ρ_c)) relation....
X-ray telescopes—NICER, eXTP, ATHENA, and STROBE-X—offer a promising probe of the structure of compact objects such as neutron stars. A dark-matter halo surrounding these objects alters the local space-time and, in turn, affects light propagation. In this work, we examine the impact of forming a self-interacting bosonic dark-matter halo around neutron stars, aiming to identify signatures that...
The neutron star equation of state (EOS) remains one of the fundamental challenges in nuclear astrophysics, with current modeling approaches facing distinct limitations. Phenomenological models, while successful in reproducing nuclear and astrophysical constraints, suffer from inherent model dependencies in their parametrizations. These dependencies can introduce biases in posterior...
The recent identification of the compact object in HESS J1731-347, with a remarkably low mass of M~0.77 solar mass and radius R~10.4 km, challenges the conventional understanding of dense matter. Such a light and compact star points to the necessity of a softer equation of state (EoS), in tension with the requirement of a stiff EoS to support massive pulsars above 2 solar mass. In this work,...
In contrast to symmetric nuclear matter, which has been extensively studied in laboratory experiments, the matter inside neutron stars is highly isospin-asymmetric. We investigate the properties of strongly interacting matter under both symmetric and neutron-star-like conditions to determine how electric charge neutrality and beta equilibrium influence the emergence of quark matter. In...
To more precisely constrain the Equation of State (EOS) of supradense neutron-rich nuclear matter, future high-precision X-ray and gravitational wave observatories are proposed to measure the radii of neutron stars (NSs) with an accuracy better than about 0.1 km. However, it remains unclear what particular aspects (other than the stiffness generally spoken of in the literature) of the EOS and...
Abstract:
Numerical relativity (NR) has revolutionized our understanding of strong-field gravity, enabling high-fidelity simulations of compact binary systems. This paper reviews recent breakthroughs in NR methodologies, with emphasis on binary neutron star (BNS) and black hole–neutron star (BHNS) mergers. We discuss advancements in adaptive mesh refinement, constraint-damping formulations,...
Observations of massive pulsars indicate that the core densities of compact stars can greatly exceed nuclear saturation density, possibly giving rise to exotic forms of matter such as hyperons, meson condensates, and quark matter. Among meson condensates, anti-kaon ($K^-$) condensation stands out as a promising candidate, though the nature of kaon-meson interactions remains incompletely...
Understanding the dynamics of magnetically arrested accretion disks (MAD) is crucial for deciphering relativistic jet launching mechanisms in black hole systems. General relativistic magnetohydrodynamics (GRMHD) simulations provide the most comprehensive framework for probing these extreme environments, where angular momentum transport efficiency fundamentally governs accretion-ejection...
We have conducted an extensive study using a diverse set of equations of state (EoSs) to uncover strong relationships between neutron star (NS) observables and the underlying EoS parameters using symbolic regression method. These EoS models, derived from a mix of agnostic and physics-based approaches, considered neutron stars composed of nucleons, hyperons, and other exotic degrees of freedom...
The relationship between cosmic strings and black holes is examined in this work, with particular attention paid to how cosmic strings affect the spin and accretion processes of black holes. The study investigates the effects of a cosmic string on the mass, spin, and rotational energy of black holes and how changes in the innermost stable circular orbit (ISCO) of accretion disks can be used to...
Abstract
We analyzed the recent controversies in the definitions of the
Feynman-Dyson propagator for the field operator. In this work we
present some insights with respect to this for spin 1/2. Both
algebraic equation $Det(\hat p − m) = 0$ and $Det(\hat p + m) = 0$ for
u− and v− 4-spinors have solutions with
$p_0 = \pm E_p = \pm \sqrt{p^2 + m^2}$. The same is true for
higher-spin...
Transiently accreting low-mass x-ray binaries have the potential to probe the core composition of their neutron stars via deep crustal heating caused by nuclear reactions. We statistically assess this deep crustal heating scenario, taking into account the various microphysical and astrophysical uncertainties. We find that despite the sizable uncertainties, there is a chance to discriminate...
The ground based gravitational wave detectors such as LIGO, measures metric perturbation in to a preferred polarization basis. The initial Ligo configuration runs were based on second post Newtonian approximation of quadrupolar moments. A post Minkowskian and a post Newtonian approach is adopted for the wave form generation of slow moving and non-spinning binaries. The non linearity of...
We investigate Tsallis holographic dark energy (THDE) model in light of modern observations of supernovae, Hubble parameter measurements, data for baryon acoustic oscillations and fluctuations of matter density. The dark energy density for THDE model is written as ρd=3C2/L4−2γ where C and γ are some constants. Scale L is infrared cut-off length for which we use the event horizon. For analysis...
