Compact Objects Research Papers - Academia.edu (original) (raw)

2025, The Astrophysical Journal

Motivated by observational searches for sub-parsec supermassive black hole binaries (SBHBs) we develop a modular analytic model to determine the likelihood for detection of SBHBs by ongoing spectroscopic surveys. The model combines the parametrized rate of orbital evolution of SBHBs in circumbinary disks with the selection effects of spectroscopic surveys and returns a multivariate likelihood for SBHB detection. Based on this model we find that in order to evolve into the detection window of the spectroscopic searches from larger separations in less than a Hubble time, 10 8 M SBHBs must, on average, experience angular momentum transport faster than that provided by a disk with accretion rate 0.06 ṀE . Spectroscopic searches with yearly cadence of observations are in principle sensitive to binaries with orbital separations < few × 10 4 r g (r g = GM/c 2 and M is the binary mass), and for every one SBHB in this range there should be over 200 more gravitationally bound systems with similar properties, at larger separations. Furthermore, if spectra of all SBHBs in this separation range exhibit the AGN-like emission lines utilized by spectroscopic searches, the projection factors imply five undetected binaries for each observed 10 8 M SBHB with mass ratio 0.3 and orbital separation 10 4 r g (and more if some fraction of SBHBs is inactive). This model can be used to infer the most likely orbital parameters for observed SBHB candidates and to provide constraints on the rate of orbital evolution of SBHBs, if observed candidates are shown to be genuine binaries.

2025, https://community.openai.com/t/beyond-shannon-a-dynamic-model-of-entropy-in-open-systems/1129493?u=mitchell\_d00

This paper proposes a formal expansion of the Dynamic Entropy Model (DEM), introducing DEM II, a post-Shannonian framework that models entropy as an emergent, recursive, and observer-sensitive flow within open systems. DEM II resolves key limitations of classical Shannon entropy by incorporating the dynamics of observation collapse, emergent probability distributions, and chaotic environmental coupling.

2025

This paper proposes a conceptual and formal expansion of the Vibrational Time Theory (VTT), reinterpreting time as an emergent frequency generated by the interaction between electromagnetic fields and the curvature of space-time. Unlike the original formulation, which used a fixed coupling parameter β, this study introduces a new modeling based on a dynamic scalar field ϕ, derived from first principles and inspired by conformal coupling approaches. With this, vibrational time becomes dependent on a triad of fundamental factors: gravitational curvature, the energy of light, and the scalar state of the universe, such that β(ϕ) = ϕ 2 /M p . Computational simulations were conducted in different astrophysical environments (white dwarfs, neutron stars, and black holes) and across various spectral energy regimes (UV, visible, and CMB). The results indicate a temporal modulation pattern consistent with the hypothesis of vibrational layers of time and reveal a possible residual spectral signature ∆λ that could be detected in observations of quasars and gravitational lenses. The new formulation expands the testability of VTT, establishes connections with scalar field theories and quantum gravity, and provides a conceptually unified framework for treating time as an emergent property of the universe's geometry and 1 energy. The study concludes with cosmological implications, limitations in sub-Planckian regimes, and proposals for future theoretical and observational developments.

2025, Journal of Physics & Optics Sciences, 7(4), pp:1-11

This study investigates Einstein-Maxwell field equations with anisotropic pressure by means of a quadratic equation of state (Bose-Einstein equation of state) in the presence of an electric field and a modified version of the metric potential proposed for Korkina and Orlyanskii (1991). We obtain new classes of models that satisfy all the physical conditions for a realistic star. According to visual analysis, physical properties including energy density, radial pressure, charge density, and anisotropy are consistent with the stellar binary system GW191219, which is composed of a neutron star and a black hole.

2025, Journal of emerging technologies and innovative research

A Neutron star is formed when an ordinary star dies and a rotating Neutron star is called a Pulsar. Study of pulsars have also been beneficial for time keeping as they are considered among the most accurate known natural time keepers. The current work is used to analyse the time period of a Pulsar using the secondary data from NASA data archive. INTRODUCTION: Pulsars are quickly rotating, extremely magnetised neutron stars that were first seen through pulsed radio emission at a very down radio observing frequency of 81 MHz. A pulsar is a highly magnetized rotating neutron star or white dwarf that is emitting a beam of electromagnetic radiation. There are different types of pulsars i.e. CRAB PULSAR and VELA PULSAR. The Crab Nebula is the supernova remnant in the constellation of Taurus. A neutron star that formed when a massive star collapsed. The Vela pulsar is about 1,000 light years away from Earth, spansis about 12 miles in diameter, and makes over 11 complete rotations every sec...

2025, Zenodo

This supporting paper elaborates on how the Elbertse Time Field Model explains the evolution of primordial mass into cosmic structure without relying on inflation, dark energy, or external forces. Through relativistic time gradients (τ-fields), the model shows how voids, filaments, and early supermassive black holes (Obscurions) form deterministically. It offers a unified explanation for cosmic web structure, CMB isotropy, and horizon homogeneity via internal time dynamics rather than metric expansion or speculative fields.

2025, Zenodo

This paper introduces the Obscurion: a gravitationally stable, non-singular compact object that can form under both stellar and cosmological conditions, depending on the gravitational environment. The Obscurion does not contain a central singularity, and its event horizon is not a mathematically sharp boundary, but rather a gradual transition zone where photons increasingly fail to escape. Central to this model is the concept of a relativistic time field that varies with gravitational curvature and background structure. We propose a modified version of General Relativity that incorporates background gravitational influence, providing a consistent explanation for compact object behavior, cosmological time variation, and quantum compatibility.

2025

The present paper is intended to build on top of existing research in r-process lanthanide production and heating rates in binary neutron star mergers (Lippuner and Roberts, 2015; Meyer et al., 1998). The r-process is thought to be responsible for the nucleosynthesis of all heavy elements in the universe. It occurs in neutron-rich environments like core-collapse supernovae and neutron star mergers. In neutron star mergers, the radioactive decay of r-process elements powers an electromagnetic transient called kilonova. The hypothesis in this paper is to introduce a possible adjustment factor for current r-process simulations and related kilo-nova heating models, which mainly use nuclear reaction networks (e.g. Lippuner and Roberts, 2017) with well-known cross-section values for all relevant atomic and particle interactions. These values are mostly published from experimental setups in laboratory conditions. As we will see, the presence of ultra-strong magnetic fields like those produced in binary neutron star mergers introduces a variety of changes to known nuclear and atomic processes (Shinkevich and Studenikin, 2019; Reiss, 1983; Arteaga et al., 2011; Ciolfi, 2020; Duncan, 2011). For example, it can make the r-process more efficient (Kondratyev, 2021). The cross-section of a given particle-nucleus interaction depend on many factors like the geometric setup, the energy of incident particles, and the spin of incident particles with respect to target nuclei, to name a few. In this paper we will only discuss changes in the geometric cross-section of neutron absorption interactions and estimate the overall effect on the total energy release for the kilonova emission. We will leave the rest of the cross-section components as topics for further discussion.

2025

We propose a novel approach to Unified Field Theory by linking gravity and electromagnetism through plasma physics. By incorporating gravitational collapse, plasma formation, and electromagnetic field generation into Einsteins equations, we derive Bommans Equation. This equation suggests that electromagnetism is an emergent phenomenon of spacetime curvature in the presence of ionized matter. The proposed framework provides a pathway to unify gravity and electromagnetism, offering new insights into astrophysical phenomena such as neutron stars, magnetars, and cosmic plasma fields.

2025, Classical and Quantum Gravity

Optical and infrared observations have thus far detected more celestial cataclysms than have been seen in gravity waves (GW). This argues that we should search for gravity wave signatures that correspond to flux variability seen at optical wavelengths, at precisely known positions. There is an unknown time delay between the optical and gravitational transient, but knowing the source location precisely specifies the corresponding time delays across the gravitational antenna network as a function of the GW-to-optical arrival time difference. Optical searches should detect virtually all supernovae that are plausible gravitational radiation sources. The transient optical signature expected from merging compact objects is not as well understood, but there are good reasons to expect detectable transient optical/IR emission from most of these sources as well. The next generation of deep wide-field surveys (for example PanSTARRS and LSST) will be sensitive to subtle optical variability, but we need to fill the "blind spots" that exist in the Galactic plane, and for optically bright transient sources. In particular, a Galactic plane variability survey at λ ∼2 µm seems worthwhile. Science would benefit from closer coordination between the various optical survey projects and the gravity wave community.

2025, HAL (Le Centre pour la Communication Scientifique Directe)

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2024, The Harmonic Universe. A New Perspective on Cosmic Interactions

The Harmonic Universe proposes a conceptual and mathematical shift in the
description of gravitational interactions and celestial motions. Based on the
idea that spacetime can be modeled as a dynamic medium, akin to a vibrating
mesh, this model redefines orbital motion as a wave phenomenon, eliminating
the need to consider gravity as a classical attractive force. This approach
does not refute Einstein’s theories but seeks to extend their scope, providing
an alternative vision capable of addressing phenomena such as dark energy,
dark matter, and the dynamic effects observed in planetary and galactic
systems. This new perspective also offers a unified vision that connects the
macroscopic dynamics of the cosmos with the fundamental principles of the
quantum world.

2024, Nuclear Fusion Tecnology

This report presents a multidisciplinary investigation combining relativistic plasma dynamics, magneto-hydrodynamics (MHD), and quantum computing-assisted simulations. Collaborations with institutions such as the MIT Quantum Engineering Lab, IBM Quantum Computing Research, Harvard Advanced Materials Group, and Lawrence Berkeley National Laboratory have yielded promising advancements. The study explores the stability and energy efficiency of Tokamak-inspired systems, anisotropic jet morphologies, and advanced fusion models using quantum-enhanced simulations to address challenges in high-dimensional modeling and experimental validation

2024, Results in Physics

FOV/Camera Pair 70° × 70° FWHM Energy Range 2-50 keV Energy Resolution 300 eV FWHM Sensitivity (1 s) 600 mcrab Sensitivity (1 day) 2 mcrab Sky Coverage (Instantaneous) 4.1 sr Angular Resolution 4.3 arcmin Position Accuracy 1 arcmin X-ray Concentrator Array (XRCA) Energy Range 0.2-12 keV Effective Area (cm^2 @ 1.5 keV) 21,760 cm2 Energy Resolution 85-175 eV FWHM Time Resolution 100 ns Collimator 4 arcmin FWHM Background Rate 2.2 c/s Count Rate on Crab (0.2-10 keV) 148,000 Large Area Detector (LAD) Energy Range 2-30 keV Effective Area (cm^2 @ 10 keV) 51,000 cm2 Energy Resolution 200-300 eV FWHM Time Resolution 10 µs Collimator 1° FWHM Count Rate on Crab (2-30 keV) 156,000 Background Rate 822 c/s (5 mcrab) 1 STROBE-X March 11, 2019 STROBE-X 's formidable capabilities will also enable a broad portfolio of additional science including accretion physics, stellar evolution, stellar flares, gamma-ray bursts, tidal disruption events, active galactic nuclei, clusters of galaxies, and axion searches. STROBE-X carries three instruments: • The X-ray Concentrator Array (XRCA) covers the soft or low-energy band (0.2-12 keV) with an array of lightweight optics (3 m focal length) that concentrate incident photons onto small solid-state detectors with CCD-level (85-175 eV) energy resolution, 100 ns time resolution, and low background rates. This technology has been fully developed for NICER and will be scaled up to take advantage of the longer focal length of XRCA, which provides an order-of-magnitude improvement in effective area over NICER with over 2.1 m 2. • The Large Area Detector (LAD) covers the harder or higher-energy band (2-30 keV or beyond), with modules of Si drift detectors and micropore collimators originally developed for the European LOFT mission concept. LAD provides an order-of-magnitude improvement in both effective area (5.1 m 2) and spectral resolution (200-300 eV) over RXTE /PCA. • The Wide-Field Monitor (WFM) will act as a trigger for pointed observations of X-ray transients and will also provide high duty-cycle, high time-resolution, and high spectralresolution monitoring of the dynamic X-ray sky over the 2-50 keV band. WFM will have 15 times the sensitivity of the RXTE All-Sky Monitor, enabling multi-wavelength and multimessenger investigations with a large instantaneous field of view, down to a new, order-ofmagnitude lower flux regime. The STROBE-X mission does not require any new technologies to be developed. The XRCA is a small modification of the flight-proven optics and detectors from NICER, while the LAD and WFM are based on large-area silicon drift detectors already used in experiments at the Large Hadron Collider as well as microchannel plate collimators that have multiple commercial vendors available. In addition, the spacecraft relies only on high-Technology Readiness Level (TRL) components. During our study, we produced detailed instrument and mission designs working with the Integrated Design Center (IDC) at NASA/GSFC. We constructed master equipment lists (MELs) down to the component level for both the instruments and the mission, and we validated our parts acquisition and screening strategy and optimized our design to facilitate manufacture, assembly, integration and test flow. Based on these efforts, we produced a realistic development schedule assuming a Phase A start of October 1, 2023 that yields a launch date of January 1, 2031. The final result of our study is a mission cost estimate. The instrument and spacecraft costs are parametric cost estimates from PRICE-H and SEER, driven by the detailed MELs and using a common set of assumptions for a Class B mission. To that hardware cost, we applied standard percentage multipliers for the other work breakdown structure (WBS) elements and 25% reserves, a 150Mfixedchargeforlaunchservicesgivingatotalmissionlifecyclecostestimateof150M fixed charge for launch services giving a total mission lifecycle cost estimate of 150Mfixedchargeforlaunchservicesgivingatotalmissionlifecyclecostestimateof880M (FY2018 dollars). This fits within the maximum probe-class budget of $1000M with an additional 13% margin beyond the reserves, giving us high confidence that this mission is executable as a probe. STROBE-X is a highly executable probe-class mission that is ready for construction in the 2020s. This mission is poised to deliver high-impact science in the 2030s that will address some of the highest priority science questions about the formation, evolution, and accretion processes of black holes, the nature of dense matter and gravity, and a wide range of cosmic explosions.

2024, arXiv (Cornell University)

Mathematical modeling within the framework of the general theory of relativity has been used to explain the behavior and structure of massive objects as neutron stars, quasars, black holes, pulsars and white dwarfs and requires finding the exact solutions of the Einstein-Maxwell system. In this paper we study the effects induced by fluctuations of local anisotropy in a new family of anisotropic solutions depending on a parameter α, whose value α=2 provides a radial pressure having the same functional dependence on the radial coordinate as the Schwarzschild solution. It is shown the effect the functional dependence on the radial coordinate has in the occurrence of cracking within the sphere when anisotropy fluctuations are allowed.

2024, Oriental Journal of Physical Sciences, Vol.09, No.(2) ,pp. 96-105

A method is developed to obtain solutions of Einstein field equations for anisotropic charged spheres. This procedure needs to choose a linear relationship between energy density and radial pressure and a metric function proposed for Buchdahl (1959). A new class of solution is obtained and subjected to several physical analyses for realistic models of compact stars. The new solutions in this research are physically reasonable, wellbehaved in the interior of the star, which indicates that these new models satisfies important physical conditions as the measure of anisotropy and matching. The models are consistent with the upper limit on the mass of compact stars for PSR J1823-3021G, PSR J1748-2446an and PSR J1518+4904.

2024, Academic Journal of Physics Research, 1(1), pp.1-8

In order to describe the properties and behavior of anisotropic charged compact stars, in this study we presented new exact solutions to the Einstein-Maxwell field equations. We assume a linear equation of state and a metric function defining a gravitational potential dependent on an adjustable parameter n. We used a relationship between gravitational potential and the electric field that helps to solve the field equations. The class of solution obtained undergoes several physical analyses for the realistic compact star models. The analysis reveals that both gravitational potentials and matter variables are well behaved and the model satisfies important physical conditions as the measure of anisotropy and matching.

2024, Journal of Physics & Optics Sciences,6(10), pp.1-7

In this paper, we studied the behavior of relativistic objects with charged anisotropic matter distribution with a linear equation of state considering a metric potential proposed for Buchdahl (1959). The new solutions to the Einstein-Maxwell system of equations are found in term of elementary functions. A physical analysis of electromagnetic field indicates that is regular in the origin and well behaved. The new obtained models satisfy all physical requirements of a physically reasonable stellar object. The models are consistent with the upper limit on the mass of compact stars for PSR J1823-3021G, PSR J1748-2446an and PSR J1518+4904.

2024

Neutron stars are remnants of supernovae explosion of massive stars upto 20-40 Mʘ at the time of their formation, neutron stars gain recoil kicks due to asymmetries that develops during the core-collapse process. Neutron stars are classified as Radio Loud and Radio Quiet. 1E 161348-5055.1 is a radio quiet neutron star found in the Centre of RCW103 which is Supernova Remnant (SNR) and is a periodic X-Ray with a period of 6.67 hours. This source was discovered by the HEAO-2 (Einstein Observatory), which is the first fully imaging X-Ray telescope. This source attracted interest due to the two main reasons. Firstly, its periodicity of 6.67 hrs which is too long for star having age 2000 years, it is behaving like a multi-million-year-old star. Secondly, the star becomes 50 times brighter in between October 1999 and January 2000. Astrophysicist put forward many theories to explain this phenomenon. In present work, the author downloaded one archived data from XMM Newton Mission and analyzed it as well as reviewed the works related to this source to understand the nature of the neutron star 1E 161348-5055.1. .

2024, Papers.ssrn.com

This paper presents a comprehensive study of metric engineering within the framework of Generalized Relativistic Symmetry Engineering, coined "GRSE" for simplicity. We aim to achieve practical applications for the manipulation of spacetime such as traversable wormholes and advanced propulsion systems. Building upon the foundations of general relativity and quantum field theory in curved spacetime, we integrate engineered symmetry fields and vacuum fluctuations to propose mechanisms that allow for the violation of classical energy conditions without resorting to unphysical forms of matter. A key contribution of this work is the incorporation of Harold Puthoff's pioneering research on vacuum engineering and zero-point energy manipulation. By harnessing vacuum fluctuations and modifying boundary conditions, we demonstrate that effective negative energy densities necessary for traversable wormholes can be generated. The GRSE framework is extended to include these quantum effects, providing a robust theoretical basis for practical metric engineering. We develop the mathematical formulation of the GRSE framework, modifying Einstein's field equations to account for symmetry fields and vacuum contributions. Specific solutions for traversable wormholes are derived, utilizing engineered scalar fields and vacuum energy manipulation to satisfy the modified field equations. The paper also addresses technological challenges and proposes experimental setups to validate the theoretical models, including precision measurements of the Casimir effect and applications of metamaterials. By unifying concepts from general relativity, quantum field theory, and vacuum engineering, this work advances the prospects of controlled spacetime manipulation. The implications of this research extend to potential breakthroughs in energy extraction, propulsion technology, and fundamental physics, paving the way for future exploration and innovation in metric engineering.

2024, Physics Letters B

We derive an equation of state (EOS) for strange matter, starting from an interquark potential which (i) has asymptotic freedom built into it, (ii) shows confinement at zero density (ρ B = 0) and deconfinement at high ρ B , and (iii) gives a stable configuration for chargeless, β-stable quark matter. This EOS is then used to calculate the structure of Strange Stars, and in particular their mass-radius relation. Our present results confirm and reinforce the recent claim[1, 2] that the compact objects associated with the x-ray pulsar Her X-1, and with the x-ray burster 4U 1820-30 are strange stars.

2024

Powerful jets in high-mass microquasars are likely to be crossed by dense inhomogeneities (clumps) from the stellar winds, which may lead to particle acceleration and thus nonthermal emission in X-rays and gamma-rays. We characterise a typical clump-jet interaction scenario and compute the contribution to the high-energy emission of these systems. We use hydrodynamical simulations of a single clump-jet interaction and we use this result to compute its non-thermal (synchrotron and inverse Compton) radiation. We present several radiative calculations for a number of clump states, as the clump is disrupted over time, letting different parameters vary (viewing angle, magnetic field). We obtain significant amounts of non-thermal radiation from jet-clump interactions in high-mass microquasars.

2024, Astronomy & Astrophysics

MAXI J1659-152 is a bright X-ray transient black-hole candidate binary system discovered in September 2010. We report here on MAXI, RXTE, Swift, and XMM-Newton observations during its 2010/2011 outburst. We find that during the first one and a half week of the outburst the X-ray light curves display drops in intensity at regular intervals, which we interpret as absorption dips. About three weeks into the outbursts, again drops in intensity are seen. These dips have, however, a spectral behaviour opposite to that of the absorption dips, and are related to fast spectral state changes (hence referred to as transition dips). The absorption dips recur with a period of 2.414 ± 0.005 h, which we interpret as the orbital period of the system. This implies that MAXI J1659-152 is the shortest period black-hole candidate binary known to date. The inclination of the accretion disk with respect to the line of sight is estimated to be 65-80 • . We propose the companion to the black-hole candidate to be close to an M5 dwarf star, with a mass and radius of about 0.15-0.25 M and 0.2-0.25 R , respectively. We derive that the companion had an initial mass of about 1.5 M , which evolved to its current mass in about 5-6 billion years. The system is rather compact (orbital separation of 1.33 R ), and is located at a distance of 8.6 ± 3.7 kpc, with a height above the Galactic plane of 2.4 ± 1.0 kpc. The characteristics of short orbital period and high Galactic scale height are shared with two other transient black-hole candidate X-ray binaries, i.e., XTE J1118+480 and Swift J1735.5-0127. We suggest that all three are kicked out of the Galactic plane into the halo, rather than being formed in a globular cluster.

2024, Arxiv preprint arXiv:0911.4627

We address the existence of globally neutral neutron star configurations in contrast with the traditional ones constructed by imposing local neutrality. The equilibrium equations describing this system are the Einstein-Maxwell equations which must be solved self-consistently with the general relativistic Thomas-Fermi equation and β-equilibrium condition. To illustrate the application of this novel approach we adopt the Baym, Bethe, and Pethick (1971) strong interaction model of the baryonic matter in the core and of the white-dwarf-like material of the crust. We illustrate the crucial role played by the boundary conditions satisfied by the leptonic component of the matter at the interface between the core and the crust. For every central density an entire new family of equilibrium configurations exists for selected values of the Fermi energy of the electrons at the surface of the core. Each such configuration fulfills global charge neutrality and is characterized by a non-trivial electrodynamical structure. The electric field extends over a thin shell of thickness ∼ /(mec) between the core and the crust and becomes largely overcritical in the limit of decreasing values of the crust mass.

2024, Universal Library of Innovative Research and Studies,1(2), pp.1-8

In this paper we obtained some spherically stellar configurations that represent new models of dark energy stars specifying particular forms for gravitational potential and the electric field intensity which allows solve the Einstein-Maxwell field equations. We have chosen the metric potential proposed by Buchdahl (1959) with the equation of state r p ωρ = where r p is the radial pressure, ρ is the dark energy density and ω is the dark energy parameter. We found that the radial pressure, the anisotropy factor, energy density, metric coefficients, mass function, charge density are regular and well behaved in the stellar interior but the causality conditions and of strong energy are not satisfied. These models have great application in physics and cosmology due to the fact that several independent observations indicate that the universe is in a phase of accelerated expansion which can be explained by the presence of dark energy that has not been detected.

2024, The Astrophysical Journal

We report results of three dimensional mangetohydrodynamical (MHD) simulations of global accretion disks threaded with weak vertical magnetic fields. We perform the simulations in the spherical coordinates with different temperature profiles and accordingly different rotation profiles. In the cases with a spatially constant temperature, because the rotation frequency is vertically constant in the equilibrium condition, general properties of the turbulence excited by magnetorotational instability (MRI) are quantitatively similar to those obtained in local shearing box simulations. On the other hand, in the cases with a radially variable temperature profile, the vertical differential rotation, which is inevitable in the equilibrium condition, winds up the magnetic field lines, in addition to the usual radial differential rotation. As a result, the coherent wound magnetic fields contribute to the Maxwell stress in the surface regions. Our global simulations give somewhat larger density fluctuation, δρ/ρ = 0.1 -0.2, near the midplane than the values obtained in previous local shearing box simulations and global simulations without net vertical magnetic field. The velocity fluctuations, dominated by the radial component, are ≈ 0.1 -0.2 of the local sound speed. The azimuthal power spectra of the magnetic fields show shallow slopes, ∝ m 0 ∼ m -1 , where m is an azimuthal mode number, which might be related to the energy injection by MRI from small scales. On the other hand, the power spectra of the velocities and density show steeper slopes, ∝ m -1 ∼ m -2 . We observe intermittent and structured disk winds driven by the Poynting flux associated with the MHD turbulence, with the slightly smaller mass fluxes than that obtained in our local simulations. The Poynting flux originating from magnetic tension is injected from the regions above a scale height toward both the midplane and the surfaces. Related to this, sound waves are directed to the midplane from the surface regions. The mass accretion mainly occurs near the surfaces and the gas near the midplane slowly moves outward in the time domain of the present simulations. The vertical magnetic fields are also dragged inward in the surface regions, while they stochastically move outward and inward around the midplane. The difference of the velocities at the midplane and the surfaces might cause large-scale meridional circulations. Applying to protoplanetary disks, these waves and circulation are supposed to play an important role in the dynamics of solid particles. We also discuss an observational implication of induced spiral structure in the simulated turbulent disks.

2024

This paper explores the influence of a black hole's spin on the formation of its accretion disk and how this affects our ability to observe black holes. Contrary to the idea that black holes accrete matter from all directions, the presence of a fixed spin axis leads to the formation of a flat accretion disk rather than a spherical shell of material. This phenomenon allows for specific observational opportunities, particularly in the context of relativistic jets and gravitational lensing effects.

2024, Journal of emerging technologies and innovative research

2024, Monthly Notices of the Royal Astronomical Society

In thisseries of papers, we shall present a simplistic approach to the study of particle dynamics, fluid dynamics and numerical simulations of accretion flows and outflows around rotating black holes. We show that with a suitably modified effective potential of the central gravitating rotating object, one can carry out these studies very accurately. In this approach, one need not use the full general relativistic equations to obtain the salient features of the general relativistic flows provided the Kerr parameter remains within −1 a 0.8. We present the equatorial and the non-equatorial particle trajectories from our potential and compare salient properties in Kerr and in pseudo-Kerr geometries. Our potential naturally produces accurate results for motions around the Schwarzschild geometry when the black hole angular momentum is set to zero.

2024, Open Access Journal of Astronomy, volume 2, issue 1

In this paper, we obtained a new class of solutions for the Einstein-Maxwell field equations with a charged anisotropic matter distribution considering the dark energy equation of state r p ωρ = , where ω is the dark energy parameter, is the radial pressure and is the energy density. We have chosen a form for the metric potential proposed for Tolman (1939) known as Tolman IV type potential. We found that the physical properties as the radial pressure, the anisotropy, energy density, mass function are regular and well behaved in the stellar interior but the strong energy condition is violated. The models are consistent with the upper limit on the mass of compact stars for Her X-1, 4U1538-52 and SAXJ1808.4-3658.

2024, American Journal of Planetary and Space Science, Volume 3 Issue 1

In this paper, we found new classes of solutions to the Einstein-Maxwell field equations with matter anisotropic distribution incorporating a particular form of electric field intensity within the framework of general relativity. We use a metric potential or ansatz that depends on an adjustable parameter n in order to get the new solutions. We generated new models of compact stars with n=1 and n=2. Graphical analysis allows us to conclude that the new models satisfy all the physical characteristics for astrophysical objects and can be very useful in the study and description of compact structures. We obtained models consistent with the pulsars PSR J1311-3430 and PSR J0952-0607.

2024

The Monitoring Spectroscopic Telescope for Energetic Radiation (MonSTER) will provide time-resolved, broadband X-ray spectroscopy (3-50 keV) of stellar mass X-ray Binary systems (XRBs) as they undergo outburst. MonSTER will be dedicated to following these sources for weeks or months at a time, with instrumentation optimized for sensitivity and spectral resolution across the crucial iron line complex that will provide a complete picture of the dynamics of key parameters such as the disk inner radius, the ionization state, and the temperature and optical depth of the corona as the outburst evolves. With flight heritage of the X-ray detectors and collimator design and modest requirements on the spacecraft bus pointing, MonSTER provides an inexpensive alternative to dedicating time from flagship missions to study accretion in extreme environments.

2024, Classical and Quantum Gravity

The general relativistic version is developed for Robertson's discussion of the Poynting-Robertson effect that he based on special relativity and Newtonian gravity for point radiation sources like stars. The general relativistic model uses a test radiation field of photons in outward radial motion with zero angular momentum in the equatorial plane of the exterior Schwarzschild or Kerr spacetime.

2024

Gravitomagnetic clock effects for circularly rotating orbits in black hole spacetimes are studied from a relative observer point of view, clarifying the roles played by special observer families.

2024, Arxiv preprint astro-ph/ …

VITRUV is a second generation spectro-imager for the PRIMA enabled Very Large Telescope Interferometer. By combining simultaneously up to 8 telescopes VITRUV makes the VLTI up to 6 times more efficient. This operational gain allows two novel scientific methodologies: 1) massive surveys of sizes; 2) routine interferometric imaging. The science cases presented concentrate on the qualitatively new routine interferometric imaging methodology. The science cases are not exhaustive but complementary to the PRIMA reference mission. The focus is on: a) the close environment of young stars probing for the initial conditions of planet formation and disk evolution; b) the surfaces of stars tackling dynamos, activity, pulsation, mass-loss and evolution; c) revealing the origin of the extraordinary morphologies of Planetary Nebulae and related stars; d) studying the accretion-ejection structures of stellar black-holes (microquasars) in our galaxy; e) unveiling the different interacting components (torus, jets, BLRs) of Active Galactic Nuclei; and f) probing the environment of nearby supermassive black-holes and relativistic effects in the Galactic Center black-hole.

2024, Monthly Notices of the Royal Astronomical Society

The Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) Coma Cluster Treasury Survey is a deep two-passband imaging survey of the nearest very rich cluster of galaxies, covering a range of galaxy density environments. The imaging is complemented by a recent wide field redshift survey of the cluster conducted with Hectospec on the 6.5-m Monolithic Mirror Telescope (MMT). Among the many scientific applications for these data is the search for compact galaxies. In this paper, we present the discovery of seven compact (but quite luminous) stellar systems, ranging from M32-like galaxies down to ultra-compact dwarfs (UCDs)/dwarf to globular transition objects (DGTOs). We find that all seven compact galaxies require a two-component fit to their light profile and have measured velocity dispersions that exceed those expected for typical early-type galaxies at their luminosity. From our structural parameter analysis, we conclude that three of the samples should be classified as compact ellipticals or M32-like galaxies, and the remaining four being less extreme systems. The three compact ellipticals are all found to have old luminosity weighted ages (12 Gyr), intermediate metallicities (−0.6 < [Fe/H] < −0.1) and high [Mg/Fe] (0.25). Our findings support a tidal stripping scenario as the formation mode of compact galaxies covering the luminosity range studied here. We speculate that at least two early-type morphologies may serve as the progenitor of compact galaxies in clusters.

2024

The Galactic black hole candidate (BHC) 4U 1630 −472 has gone through several outbursts (13 to be particular) in the last two and a half decades starting from the RXTE era till date. Like the outbursts of other transient BHCs, the outbursts of this source show variations in duration, peak numbers, highest peak flux, etc. Ho we ver, unlike other soft X-ray transients, this source showed outbursts of two types, such as normal and super. The normal outbursts of duration ∼100 −200 d are observed with an average recurrence or quiescence period of ∼500 d. The super outbursts of duration ∼1.5 −2.5 yr, consist of more than one normal outburst and one mega outburst. We make an effort to separate the flux contributions of the normal and mega components from the super outbursts, and try to understand the nature of evolution of both types (normal and mega) of outbursts, based on the quiescent period prior to the outbursts.

2024

In 2016-17, the Galactic transient black hole candidate GRS 1716-249 exhibited an outburst event after a long quiescence period of almost 23 years. The source remained in the outbursting phase for almost 9 months. We study the spectral and temporal properties of the source during this outburst using archival data from four astronomy satellites, namely MAXI, Swift, NuSTAR and AstroSat. Initial spectral analysis is done using combined disk black body and power-law models. For a better understanding of the accretion flow properties, we studied spectra with the physical two component advective flow (TCAF) model. Accretion flow parameters are extracted directly from the spectral fits with the TCAF model. Low frequency quasi periodic oscillations are also observed in the Swift/XRT and AstroSat/LAXPC data. From the spectral fit, we also estimate the probable mass of GRS 1716-249 to be in the range of 4.50-5.93M or 5.01 +0.92 −0.51 M. Refitting of all spectra is done by freezing the mass at its average value. An insignificant deviation of the TCAF model parameters is observed. From the nature of the variation of the newly fitted spectral and temporal properties, we find that the source stays in only the harder (hard and hard-intermediate) states during the outburst. It does not make a transition to the softer states which makes it a 'failed' outburst.

2024

Spectral and timing properties of the stellar-mass black hole candidate XTE J1752-223 during its 2009-10 outburst are studied using RXTE PCA data in the 2.5-25 keV energy range. Low frequency quasi-periodic oscillations are seen during outburst. The spectral analysis is done using two types of models: one is the combined disc blackbody plus power-law model and the other is Transonic flow solution based Two Component Advective Flow (TCAF) model. Light-curve profiles and evolution of hardness ratios are studied using MAXI GSC and Swift BAT data. Based on the evolution of the temporal and the spectral properties, we find that the object evolved through the following spectral states: hard, hard-intermediate, and soft-intermediate/soft. From the TCAF model fitted spectral analysis, we also estimate the probable mass of the black hole in the range of 8.1-11.9 M , and more precisely, the mass appears to be 10 ± 1.9 M .

2024, The Astrophysical Journal

Transient black hole candidates are interesting objects to study in X-rays as these sources show rapid evolutions in their spectral and temporal properties. In this paper, we study the spectral properties of the Galactic transient X-ray binary MAXI J1659-152 during its very first outburst after discovery with the archival data of RXTE Proportional Counter Array instruments. We make a detailed study of the evolution of accretion flow dynamics during its 2010 outburst through spectral analysis using the Chakrabarti-Titarchuk two-component advective flow (TCAF) model as an additive table model in XSPEC. Accretion flow parameters (Keplerian disk and sub-Keplerian halo rates, shock location, and shock strength) are extracted from our spectral fits with TCAF. We studied variations of these fit parameters during the entire outburst as it passed through three spectral classes: hard, hard-intermediate, and soft-intermediate. We compared our TCAF fitted results with standard combined disk blackbody (DBB) and power-law (PL) model fitted results and found that variations of disk rate with DBB flux and halo rate with PL flux are generally similar in nature. There appears to be an absence of the soft state, unlike what is seen in other similar sources.

2024, Valtonen Mauri Karttunen Hannu

How do three celestial bodies move under their mutual gravitational attraction? This problem was studied by Isaac Newton and other leading mathematicians over the last two centuries. Poincaré's conclusion, that the problem represents an example of chaos in nature, opens the new possibility of using a statistical approach. For the first time this book presents these methods in a systematic way, surveying statistical as well as more traditional methods.

2024, Classical and Quantum Gravity

The well-known Regge-Wheeler equation describes the axial perturbations of Schwarzschild metric in the linear approximation. From a mathematical point of view it presents a particular case of the confluent Heun equation and can be solved exactly, due to recent mathematical developments. We present the basic properties of its general solution. A novel analytical approach and numerical techniques for study the boundary problems which correspond to quasi-normal modes of black holes and other simple models of compact objects are developed.

2024, Arxiv preprint gr-qc/0603003

We solve the Regge-Wheeler equation for axial perturbations of the Schwarzschild metric in the black hole interior in terms of Heun's functions and give a description of the spectrum and the eigenfunctions of the interior problem. The... more

2024, Springer eBooks

Gravitational magnetism (or the Blackett effect) is the generation of a magnetic field by an electrically neutral rotating mass, whose magnitude is determined by analogy with the magnetic field generated by a rotating electric charge. Since 1947, there is increasing evidence for this effect by the measurements of the magnetic fields of the solar planets, the sun, other stars, and even pulsars, as well as the galactic magnetic field. However, the attempt to measure this effect in the laboratory depends on the ability to measure extremely weak magnetic fields and the shielding of extraneous magnetic fields. Early attempts to measure this effect in the laboratory depended on ad hoc extensions of the simple rotational version of gravitational magnetism. Recently there have been more sophisticated laboratory approaches. Also the extended observational evidence has generated a plethora of theoretical attempts to derive the Blackett equation in a larger context. Of particular interest is the work of R.I. Gray, who performed an advanced version of Blackett's static experiment, and also related the Blackett effect to several other theoretical and empirical relations particularly the Wesson effect-the constancy of the ratio of spin to mass-squared for planetary, stellar, and galactic bodies. Pauli's anomalous magnetic moment (as a Blackett effect) is also considered as a bridge to the gravitomagnetic field generated by superconductors.

2024, General Relativity and Gravitation

We study the generation of a stochastic gravitational wave (GW) background produced by a population of neutron stars (NSs) which go over a hadron-quark phase transition in its inner shells. We obtain, for example, that the NS phase transition, in cold dark matter scenarios, could generate a stochastic GW background with a maximum amplitude of hBG ∼ 10 −24 , in the frequency band ≃ 20 − 2000 Hz for stars forming at redshifts of up to z ≃ 20. We study the possibility of detection of this isotropic GW background by correlating signals of a pair of 'advanced' LIGO observatories.

2024, 72nd International Astronautical Congress (IAC), Dubai

In recent years CubeSats have transcended their original purpose of being an educational and technology demonstration platform only. It has now brought in reach affordable yet state-of-the-art Earth observation missions to academia, governments, and private industry. ISISpace has taken up its share by supporting this Earth observation trend with the launch of NAPA-1 in September 2020, it being the first Earth Observation CubeSat of the Royal Thai Airforce. Successful commissioning and the transfer of operations to the customer has led to valuable feedback and lessons learnt. These have been directly put to use during the design and development of its successor NAPA-2. NAPA-2 takes small satellite Earth observation up a notch thanks to its multispectral imager: the Simera MultiScape100 CIS. This not only means an upgrade from NAPA-1's 50-meter ground sampling distance (GSD) to a stunning 5-meter GSD, but also being able to scan the surface in up to 7 spectral bands at the same time. Implications of this, however, are stricter platform requirements to meet optical performance and the need for dedicated on-ground image processing capability. The latter is achieved by the inclusion of Pinkmatter Solutions' FarEarth application. While images and satellite data obtained and lessons learnt throughout the NAPA-1 commissioning period will be shared, this paper will focus on the improvements made and the resulting differences with the next generation satellite NAPA-2. Insight into its design and in-orbit performance will be provided. On top of that, the assembly, integration, and verification phase will be elaborated on. It will also include details on the on ground optical verification of the MultiScape100 CIS, showing how verification before and after, for example, environmental testing was achieved. Finally, an outlook will be given to show the next steps in the coming years at ISISpace regarding small satellite Earth observation and image processing.

2024

The ixRD is the primary science payload on Sharjah-Sat-1, a 3U CubeSat expected to be launched in Q4, 2022. Its main scientific goal is monitoring bright hard X-ray sources and transients in 20 - 200 keV band. The iXRD consists of a CdZnTe crystal (6.45 cm2 area, 5 mm thickness), a Tungsten collimator with square holes with an opening angle of 4.26o, readout and control electronics and power circuitry, a back-shield and mechanical structures. Some of the design elements of iXRD have been inherited from the XRD on BeEagleSat with significant improvements in terms of collecting area, X-ray background and electronic noise. In this article, the design of the iXRD is discussed in detail taking into account mechanical, electronics, control software and data handling aspects. Its expected performance is determined after ground calibration. Depending on the pixel size, the energy resolution is 4 - 7 keV at 60 keV and the minimum detectable energy is 19 - 23 keV.

2024, Experimental Astronomy

The Chasing All Transients Constellation Hunters (CATCH) space mission plans to launch three types of micro-satellites (A, B, and C). The type-B CATCH satellites are dedicated to locating transients and detecting their time-dependent energy spectra. A type-B satellite is equipped with lightweight Wolter-I X-ray optics and an array of position-sensitive multi-pixel Silicon Drift Detectors. To optimize the scientific payloads 1

2024, Astrophysics and Space Science

The inner structure of a star or a primordial interstellar cloud is a major topic in classical and relativistic physics. The impact that General Relativistic principles have on this structure has been the subject of many research papers. In this paper we consider within the context of General Relativity a prototype model for this problem by assuming that a star consists of polytropic gas. To justify this assumption we observe that stars undergo thermodynamically irreversible processes and emit heat and radiation to their surroundings. Due to the emission of this energy it is worthwhile to consider an idealized model in which the gas is polytropic. To find interior solutions to the Einstein equations of General Relativity in this setting we derive a single equation for the cumulative mass distribution of the star and use Tolman-Oppenheimer-Volkoff equation to derive formulas for the isentropic index and coefficient. Using these formulas we present analytic and numerical solutions for the polytropic structure of self-gravitating stars and examine their stability. We prove also that when the thermodynamics of a star as represented by the isentropic index and coefficient is known, the corresponding matter density within the star is uniquely determined.