Massive Astrophysical Objects Research Articles

Tidal effect on the gyroscopic precession around a compact star

General relativistic effects around massive astrophysical objects can be captured using a test gyro orbiting the object in a circular geodesic. This paper discusses how the tidal field due to a companion object affects the spin precession frequency and orbital angular velocity of a spinning gyro orbiting around a compact astrophysical object. The precession frequency is studied in a region of space around the central object using a perturbative approach. The central object is either a neutron star or a white dwarf in this study. The test gyro is any planetary or asteroid-like object orbiting a neutron star or a white dwarf. Moreover, the companion object that causes the tidal field can be a neutron star, white dwarf or a stellar black hole. It is seen that the tidal effect significantly affects the spacetime around the central object, which affects the gyro precession frequency and the orbital angular velocity. Slow rotation approximation has been considered for the central object, which creates negligible deformation. The change in the gyro’s precession frequency and the orbital angular velocity due to the tidal field increases with an increase in the companion object’s mass and decreases as the separation between the central star and the companion star increases. The tidal effect also varies with the stiffness of the equation of state of matter describing the host star. The lower the compactness of the host star, the greater is the tidal response; thus the greater is the change in the gyro’s precession and angular velocity of the geodesic.

An Eccentric Binary Blackhole in Post-Newtonian Theory

Gravitational waves radiated during binary black hole coalescence are a perfect probe for studying the characteristics of strong gravity. Advanced techniques for creating numerical relativity substitute models for eccentric binary black hole systems are presumed to be crucial in existing and anticipated gravitational wave detectors. The imprint on the observation data of the gravitational wave emitted by the binary coalescence enhances two-body system studies. The aim of this study is to present an overview of the change in characteristic behaviors of hierarchical massive astrophysical objects merger, which are the databank of the early universe. We present results from numerical relativity simulations of an equal-mass and unequal mass nonspinning inspiral binary-black-hole system in the Post-Newtonian framework. We also consider the time evolution of eccentricity for an initial eccentric system. The eccentric Post-Newtonian equations are expanded in the form of the frequency related variable x=(Mω)2/3. The model is restricted to the (2, 2) spin-weighted spherical harmonic modes. We conclude that for higher eccentricity as well as mass ratio, there is higher oscillation in orbital radius and in eccentricity.

Fundamental Gravity and Gravitational Waves

While being as old as general relativity itself, the gravitational two-body problem has never been under so intense investigation as it is today, spurred by both phenomenological and theoretical motivations. The observations of gravitational waves emitted by compact binary coalescences bear the imprint of the source dynamics, and as the sensitivity of detectors improve over years, more accurate modeling is being required. The analytic modeling of classical gravitational dynamics has been enriched in this century by powerful methods borrowed from field theory. Despite being originally developed in the context of fundamental particle quantum scatterings, their applications to classical, bound system problems have shown that many features usually associated with quantum field theory, such as, e.g., divergences and counterterms, renormalization group, loop expansion, and Feynman diagrams, have only to do with field theory, be it quantum or classical. The aim of this work is to present an overview of this approach, which models massive astrophysical objects as nonrelativistic particles and their gravitational interactions via classical field theory, being well aware that while the introductory material in the present article is meant to represent a solid background for newcomers in the field, the results reviewed here will soon become obsolete, as this field is undergoing rapid development.

On the Identification of Individual Gravitational-wave Image Types of a Lensed System Using Higher-order Modes

Abstract Similarly to light, gravitational waves can be gravitationally lensed as they propagate near massive astrophysical objects such as galaxies, stars, or black holes. In recent years, forecasts have suggested a reasonable chance of strong gravitational-wave lensing detections with the LIGO–Virgo–KAGRA detector network at design sensitivity. As a consequence, methods to analyze lensed detections have seen rapid development. However, the impact of higher-order modes on the lensing analyses is still under investigation. In this work, we show that the presence of higher-order modes enables the identification of individual image types for the observed gravitational-wave events when two lensed images are detected, which would lead to unambiguous confirmation of lensing. In addition, we show that higher-order mode content can be analyzed more accurately with strongly lensed gravitational-wave events.

Beyond the Detector Horizon: Forecasting Gravitational-Wave Strong Lensing

Abstract When gravitational waves pass near massive astrophysical objects, they can be gravitationally lensed. The lensing can split them into multiple wave fronts, magnify them, or imprint beating patterns on the waves. Here we focus on the multiple images produced by strong lensing. In particular, we investigate strong lensing forecasts, the rate of lensing, and the role of lensing statistics in strong lensing searches. Overall, we find a reasonable rate of lensed detections for double, triple, and quadruple images at the LIGO–Virgo–KAGRA design sensitivity. We also report the rates for A+ and LIGO Voyager and briefly comment on potential improvements due to the inclusion of subthreshold triggers. We find that most galaxy-lensed events originate from redshifts z ∼ 1–4 and report the expected distribution of lensing parameters for the observed events. Besides forecasts, we investigate the role of lensing forecasts in strong lensing searches, which explore repeated event pairs. One problem associated with the searches is the rising number of event pairs, which leads to a rapidly increasing false alarm probability. We show how knowledge of the expected galaxy-lensing time delays in our searches allow us to tackle this problem. Once the time delays are included, the false alarm probability increases linearly (similar to nonlensed searches) instead of quadratically with time, significantly improving the search. For galaxy cluster lenses, the improvement is less significant. The main uncertainty associated with these forecasts are the merger-rate density estimates at high redshift, which may be better resolved in the future.

A fast and precise methodology to search for and analyse strongly lensed gravitational-wave events

ABSTRACT Gravitational waves, like light, can be gravitationally lensed by massive astrophysical objects such as galaxies and galaxy clusters. Strong gravitational-wave lensing, forecasted at a reasonable rate in ground-based gravitational-wave detectors such as Advanced LIGO, Advanced Virgo, and KAGRA, produces multiple images separated in time by minutes to months. These images appear as repeated events in the detectors: gravitational-wave pairs, triplets, or quadruplets with identical frequency evolution originating from the same sky location. To search for these images, we need to, in principle, analyse all viable combinations of individual events present in the gravitational-wave catalogues. An increasingly pressing problem is that the number of candidate pairs that we need to analyse grows rapidly with the increasing number of single-event detections. At design sensitivity, one may have as many as $\mathcal {O}(10^5)$ event pairs to consider. To meet the ever-increasing computational requirements, we develop a fast and precise Bayesian methodology to analyse strongly lensed event pairs, enabling future searches. The methodology works by replacing the prior used in the analysis of one strongly lensed gravitational-wave image by the posterior of another image; the computation is then further sped up by a pre-computed lookup table. We demonstrate how the methodology can be applied to any number of lensed images, enabling fast studies of strongly lensed quadruplets.

Effect of rotation and magnetic field in the gyroscopic precession around a neutron star

General relativistic effects are essential in defining the spacetime around massive astrophysical objects. The effects can be captured using a test gyro. If the gyro rotates at some fixed orbit around the star, then the gyro precession frequency captures all the general relativistic effects. In this article, we calculate the overall precession frequency of a test gyro orbiting a rotating neutron star or a rotating magnetar. We find that the gyro precession frequency diverges as it approaches a black hole, whereas, for a neutron star, it always remains finite. For a rotating neutron star, a prograde motion of the gyro gives a single minimum, whereas a retrograde motion gives a double minimum. We also find that the gyroscope precession frequency depends on the star’s mass and rotation rate. Depending on the magnetic field configuration, we find that of the precession frequency of the gyro differs significantly inside the star; however, outside the star, the effect is not very prominent. Also, the gyro precession frequency depends more significantly on the star’s rotation rate than its magnetic field strength.

Updating the MACHO fraction of the Milky Way dark halowith improved mass models

Recent interest in primordial black holes as a possible dark matter candidate has motivated the reanalysis of previous methods for constraining massive astrophysical compact objects in the Milky Way halo and beyond. In order to derive these constraints, a model for the dark matter distribution around the Milky Way must be used. Previous microlensing searches have assumed a semi-isothermal density sphere for this task. We show this model is no longer consistent with data from the Milky Way rotation curve, and test two replacement models, namely NFW and power-law. The power-law model is the most flexible as it can break spherical symmetry, and best fits the data. Thus, we recommend the power-law model as a replacement, although it still lacks the flexibility to fully encapsulate all possible shapes of the Milky Way halo. We then use the power-law model to rederive some previous microlensing constraints in the literature, while propagating the primary halo-shape uncertainties through to our final constraints. Our analysis reveals that the microlensing constraints towards the Large Magellanic Cloud weaken somewhat for MACHO masses around $10\, M_\odot$ when this uncertainty is taken into account, but the constraints tighten at lower masses. Exploring some of the simplifying assumptions of previous constraints we also study the effect of wide mass distributions of compact halo objects, as well as the effect of spatial clustering on microlensing constraints. We find that both effects induce a shift in the constraints towards smaller masses, and can effectively remove the microlensing constraints from $M \sim 1-10 M_\odot$ for certain MACHO populations.

Neutron stars structure in the context of massive gravity

Motivated by the recent interests in spin−2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

Evolution and dynamical properties of Bose-Einstein condensate dark matter stars

Using recently developed nonrelativistic numerical simulation code, we investigate the stability properties of compact astrophysical objects that may be formed due to the Bose-Einstein condensation of dark matter. Once the temperature of a boson gas is less than the critical temperature, a Bose-Einstein condensation process can always take place during the cosmic history of the Universe. Because of dark matter accretion, a Bose-Einstein condensed core can also be formed inside massive astrophysical objects such as neutron stars or white dwarfs, for example. Numerically solving the Gross-Pitaevskii-Poisson system of coupled differential equations, we demonstrate, with longer simulation runs, that within the computational limits of the simulation the objects we investigate are stable. Physical properties of a self-gravitating Bose-Einstein condensate are examined both in nonrotating and rotating cases.

On slow flows of a weakly stratified relativistic fluid in a static gravitational field

Simplified equations for slow flows of a weakly stratified (in entropy) fluid inside or near a massive astrophysical object have been derived from the variational formulation of ideal general relativistic hydrodynamics under the conditions that the gravitational field in the leading order is centrosymmetric and static and that the effect of a magnetic field is negligibly small. Internal waves and vortices in such systems are soft modes as compared to sound. This circumstance allows the formulation of a “soundproof” Hamiltonian model. This model is an analog of nonrelativistic hydrodynamic anelastic models, which are widely used in studies of internal waves and/or convection in spatially inhomogeneous compressible media in atmospheric physics, geophysics, and astrophysics.

Energy Transfer and Fluid Flow around a Massive Astrophysical Object

In this work it is presented the modeling and simulation of energy transfer and fluid flow of a stationary spherical arrangement of particles surrounding a gravitational body such as an astrophysical object that carries the curvature of space-time continuum in general relativity, taking into account the thermodynamics of the second law. This model also predicts the drag of space and time around an astrophysical object as it rotates, with results close to the experimental data reported by other authors. To model the energy transfer of the mass and the fluid flow in the space-time, it is used a 4-dimensional system. In order to make measurements of entropy in the arrow of time (past-present), tensors in General Relativity were used to calculate this thermodynamic quantity and with this, the big bang ́s low entropy condition in phase space of coarse graining (Hawking ́s box), according to Weyl curvature hypothesis (WCH) of Roger Penrose. Contribution of this paper is presented by tensors which carry information that has to do with something as non-distortion effect in fluid flow around the astrophysical object and the low entropy condition that is believed to exist in the past, in the big bang; what leads us to search for a new physical-mathematical science to continue. At this point, the Einstein field equations are out of context, which leads us to conclude that it is necessary a mathematical science that allows us to make calculations to rescue lost information due to collapse of matter to a black hole. This math should allow us to clear up physical phenomena (like origin of the universe) and their relationship, with the objective of unifying theories that lead to a physical science without uncertainties, as at the present time. In this regard, we propose a metric in hyperbolic coodinates to build a physical wormhole shaped object where gravitational bodies can be housed that allow us to link the past entropy with the present entropy according to the second law of thermodynamics, as a kind of mathematical space or alternative model to compensate in some way, the link between WCH and the phase space volume of the Hawking's box, and the link between WCH and the quantum-mechanical state-vector reduction, , proposed by Penrose which still have not been determined by any author. Nomenclature

Twisting of light around rotating black holes

Kerr black holes are among the most intriguing predictions of Einstein's general relativity theory. These rotating massive astrophysical objects drag and intermix their surrounding space and time, deflecting and phase-modifying light emitted nearby them. We have found that this leads to a new relativistic effect that imposes orbital angular momentum onto such light. Numerical experiments, based on the integration of the null geodesic equations of light from orbiting point-like sources in the Kerr black hole equatorial plane to an asymptotic observer, indeed identify the phase change and wavefront warping and predict the associated light-beam orbital angular momentum spectra. Setting up the best existing telescopes properly, it should be possible to detect and measure this twisted light, thus allowing a direct observational demonstration of the existence of rotating black holes. Since non-rotating objects are more an exception than a rule in the Universe, our findings are of fundamental importance.

Polarization of a plasma in massive astrophysical objects

The macroscopic polarization of a plasma in massive astrophysical objects, which is created by gravitational and other inertial forces acting on a mass, is discussed. An additional polarization source, which appears due to the effect of Coulomb nonideality induced by the strong Coulomb interaction between charged particles, is considered. The solution of the problem can be obtained in the form of a final compact expression for a simplified case of a completely equilibrium (isothermal) star without the relativistic and magnetic-field effects. The variation formulation of statistical mechanics leads to the global equilibrium condition as an extremum of the thermodynamic potential of the star as a whole, as well as to two equivalent local forms of such an equilibrium condition in terms of the constancy of the sum of the potentials including the generalized electrochemical potential and the total balance of forces acting on each charged particle. The hypothetical consequences of the polarization of the plasma in the thermodynamics of massive astrophysical objects including the existence of a macroscopic charge localized at any interface deep in the star are discussed. The possible mechanisms of the suppression of hydrodynamic instability in massive astrophysical objects owing to the almost complete compensation (“screening”) of the effect of the gravitational field acting on each heavy charge particle by the electrostatic polarization field are analyzed.

Plasma Polarization in High Gravity Astrophysical Objects

AbstractMacroscopic plasma polarization, which is created by gravitation and other mass‐acting (inertial) forces in massive astrophysical objects (MAO) is under discussion. Non‐ideality effect due to strong Coulomb interaction of charged particles is introduced into consideration as a new source of such polarization. Simplified situation of totally equilibrium isothermal star without relativistic effects and influence of magnetic field is considered. The study is based on variational approach combined with “local density approximation”. It leads to two local forms of thermodynamic equilibrium conditions: constancy for generalized (electro)chemical potentials and/or conditions of equilibrium for the forces acting on each charged specie. New “non‐ideality potential” and “non‐ideality force” appear naturally in this consideration. Hypothetical sequences of gravitational, inertial and non‐ideality polarization on thermo‐ and hydrodynamics of MAO are under discussion (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Plasma polarization in massive astrophysical objects

Macroscopic plasma polarization, which is created by gravitation and other mass-acting (inertial) forces in massive astrophysical objects (MAOs), is under discussion. A non-ideality effect due to strong Coulomb interaction of charged particles is introduced into consideration as a new source of such polarization. A simplified situation of a totally equilibrium isothermal star without relativistic effects and influence of magnetic field is considered. The study is based on a density functional approach combined with a ‘local density approximation’. It leads to conditions of constancy for generalized (electro) chemical potentials and/or conditions of equilibrium for the forces acting on each charged species. A new ‘non-ideality force’ appears in this consideration. Hypothetical sequences of gravitational, inertial and non-ideality polarization on thermo- and hydrodynamics of MAO are under discussion.

Mass screening in modified gravity

Models of modified gravity introduce extra degrees of freedom, which for a consistency with the data, should be suppressed at observable scales. In the models that share properties of massive gravity such a suppression is due to nonlinear interactions: an isolated massive astrophysical object creates a halo of a nonzero curvature around it, shielding its vicinity from the influence of the extra degrees of freedom. We emphasize that the very same halo leads to a screening of the gravitational mass of the object, as seen by an observer beyond the halo. We discuss the case when the screening could be very significant and may rule out, or render the models observationally interesting.

Behaviour of matter close to the event horizon

ABSTRACT Investigation of the behaviour of accreting matter close to the black hole event horizonis of fundamental importance in relativistic and high energy astrophysics because theyprovide the key features of the diagnostic spectra of the stellar mass and super-massiveblack holes. In this paper, we examine the terminal behaviour of general relativis-tic matter in multi-transonic, advective black hole accretion discs. We compute, forthe first time we believe, the values of various dynamical and thermodynamic multi-transonic flow variables extremely close (≤0.01 r g ) to the event horizon and study thedependence of these variables on fundamental accretion parameters. Our calculationis useful for a better understanding of Hawking radiation from acoustic black holes.Key words: Accretion, accretion discs — black hole physics — general relativity —hydrodynamics — Hawking Radiation 1 INTRODUCTIONGravitational capture of surrounding fluid by massive astrophysical objects is known as accretion. There remains a major dif-ference between black hole (BH) accretion and accretion onto other cosmic objects including neutron stars and white dwarfs.For celestial bodies other than black holes, infall of matter terminates either by a direct collision with the hard surface of theaccretor or with the outer boundary of the magneto-sphere, resulting the luminosity through energy release from the surface.Whereas for black hole accretion, matter ultimately dives through the event horizon from where radiation is prohibited toescape according to the rule of classical general relativity (GR) and the emergence of luminosity occurs on the way towardsthe black hole event horizon. The efficiency of accretion process may be thought as a measure of the fractional conversion ofgravitational binding energy of matter to the emergent radiation and is considerably high for black hole accretion comparedto accretion onto any other astrophysical objects. Hence accretion onto classical astrophysical black holes has been recognizedas a fundamental phenomena of increasing importance in relativistic and high energy astrophysics (Frank, King & Raine1992, hereafter FKR, Shapiro & Teukolsky 1983). The extraction of gravitational energy from the black hole accretion isbelieved to power the energy generation mechanism of X-ray binaries and of the most luminous objects of the Universe, theQuasars and active galactic nuclei (AGN). The BH accretion is, thus, the most appealing way through which the all pervadingpower of gravity is explicitly manifested. If the infalling matter does not possess intrinsic angular momentum, accretion flowremains spherically symmetric. However, Inter stellar / intergalactic fluid is always likely to posses non-vanishing rotationalenergy, sufficient to dynamically break the spherical symmetry, and in almost all real physical situations, accreting matter isthrown into circular orbits around the central accretor, leading to the formation of the accretion disc around the galactic andextra-galactic black holes.If the instantaneous dynamical velocity and local acoustic velocity of the accreting fluid, moving along a space curve parame-terized by r, are u(r) and a(r) respectively, then the local Mach number M(r) of the fluid can be defined as M(r) =

LIGO data analysis

Abstract Gravitational waves promise to provide new information about massive astrophysical objects in the universe. Technological advances and engineering experience have finally made it feasible to construct detectors with sufficient sensitivity to detect the extremely weak waves which are believed to reach Earth. The Laser Interferometer Gravitational-Wave Observatory (LIGO) project has constructed two “observatories” in the United States which are poised to begin collecting scientifically interesting data. The LIGO Data Analysis System has been designed to support various types of scientific analysis to be performed using this data; its components include an interface to the raw data archive, a “Beowulf” cluster of PCs for parallel processing, and a database to store data analysis products. Attention has also been paid to the deployment of client interface programs and utility software to scientists throughout the LIGO Scientific Collaboration.

Gravitational microlensing in NUT space

We study the theoretical signature of magnetic masses on the light curve of gravitational microlensing effect in NUT space. The light curves for microlensing events in NUT space are presented and contrasted with those due to lensing produced by normal matter. In the next step, associating magnetic mass to massive astrophysical compact objects (MACHOs), we try to see its effect on the light curves of microlensing candidates observered by the MACHO group. Presence or absence of this feature in the observed microlensing events can shed light on the question of the existence of magnetic masses in the Universe.