Hole Systems Research Articles

Blazar S 0528+134 is possibly the most powerful emitter in the Universe, including in the range of gravitational waves

A new method of determining the parameters of close binary systems of supermassive black holes (SMBHs) and the level of gravitational waves (GWs) on the Earth's surface are proposed. Data are presented from long-term monitoring of possibly the most powerful emitter in the Universe, S 0528+134, at five frequencies in the radio range from 4.8 GHz to 37 GHz, obtained by the RT-22 radio telescope of the Radio Astronomy Laboratory CrAO in Simeiz, the RT-26 radio telescope at Michigan Observatory, and the 40 m radio telescope of the Owens Valley Radio Observatory. The dynamics of powerful flares that have occurred in the object since its discovery in a sky survey in 1970 were considered. The main physical characteristics of binary SMBHs located in the central regions of the system were obtained. These data were used to find the masses of the SMBH companions, the parameters of their orbits, the energy reserve of the system, and the lifetime of the object before the SMBHs' merger. The level of GWs on the Earth's surface was determined and the possibility of their detection by International Pulsar Timing Array (IPTA) GW detectors was considered.

Circumbinary Disk Spectra Irradiated by Two Central Accretion Disks in a Binary Black Hole System

We study the effect of irradiation from two accretion disks (minidisks) around respective black holes of stellar-to-intermediate masses in a circular binary on the spectrum of a circumbinary disk (CBD) surrounding them. We assume the CBD to be a standard disk and adopt the orbit-averaged irradiation flux because the viscous timescale is much longer than the orbital period. We then solve the energy equation both analytically and numerically to compute the CBD temperature distribution and the corresponding disk spectrum. We find that the analytically calculated spectra are in good agreement with the numerical ones. The CBD spectrum is almost independent of the binary mass ratio. We also find that the combined spectra of two minidisks and the CBD have double peaks, one peak in the soft X-ray band and the other in the infrared (IR) band. The former peak comes from the two minidisks, while the latter peak from the CBD. The observed flux density increases with frequency as ν 1/3 toward the soft X-ray peak, while it decreases with frequency away from the IR peak as ν −5/3. The latter feature is testable with near-IR observations with Subaru and JWST.

Thermodynamics and null geodesics of a Schwarzschild black hole surrounded by a Dehnen type dark matter halo

In this work, we derive a novel black hole solution surrounded by a Dehnen-(1,4,0) type dark matter halo by embedding a Schwarzschild black hole within the halo, constituting a composite dark matter-black hole system. The thermodynamics of the resulting effective black hole spacetime is then studied with particular attention to the influence of the dark matter parameters on various thermodynamic properties. We examine the specific heat and free energy to assess the thermodynamic stability of the model. Furthermore, the null geodesics and the effective potential of light rays are studied to investigate how the dark matter parameters affect these geodesics and the radii of circular orbits. The stability of circular null geodesics is analysed using dynamical systems and Lyapunov exponents, which represent the dynamical behaviour of the circular photon orbits. Finally, we studied if the circular geodesics exhibit chaotic behaviour using the chaos-bound condition.

Discovery of persistent quasi-periodic oscillations in accreting white dwarfs: a new link to X-ray binaries

ABSTRACT Almost all accreting black hole and neutron star (NS) X-ray binary systems (XRBs) exhibit prominent brightness variations on a few characteristic time-scales and their harmonics. These quasi-periodic oscillations (QPOs) are thought to be associated with the precession of a warped accretion disc, but the physical mechanism that generates the precessing warp remains uncertain. Relativistic frame dragging (Lense–Thirring precession) is one promising candidate, but a misaligned magnetic field is an alternative, especially for NS XRBs. Here, we report the discovery of five accreting white dwarf systems (AWDs) that display strong optical QPOs with characteristic frequencies and harmonic structures that suggest they are the counterpart of the QPOs seen in XRBs. Since AWDs are firmly in the classical (non-relativistic) regime, Lense–Thirring precession cannot account for these QPOs. By contrast, a weak magnetic field associated with the white dwarf can drive disc warping and precession in these systems, similar to what has been proposed for NS XRBs. Our observations confirm that magnetically driven warping is a viable mechanism for generating QPOs in disc-accreting astrophysical systems, certainly in AWDs and possibly also in NS XRBs. Additionally, they establish a new way to estimate magnetic field strengths, even in relatively weak-field systems where other methods are not available.

A Comparison of the X-Ray Polarimetric Properties of Stellar and Supermassive Black Holes

X-ray polarization provides a new way to probe accretion geometry in black hole systems. If the accretion geometry of black holes is similar regardless of mass, we should expect the same to be true of their polarization properties. We compare the polarimetric properties of all nonblazar black holes observed with the Imaging X-ray Polarimetry Explorer. We find that their polarization properties are very similar, particularly in the hard state, where the corona dominates. This tentatively supports the idea that stellar and supermassive black holes share a common coronal geometry.

Exploring the Broadband Spectral and Timing Characteristics of GRS 1915+105 with AstroSat and NICER Observations

In this study, we undertake a spectral-timing analysis of the black hole X-ray binary source GRS 1915+105 using simultaneous observations carried out by AstroSat (Large Area X-ray Proportional Counter, LAXPC and Soft X-ray Telescope, SXT) and Neutron Star Interior Composition Explorer (NICER) in 2017. The source showed two flux levels (high and low), whose energy spectra can be described by the thermal comptonization of disk photons. The spectral parameters obtained by the joint fitting of SXT/LAXPC and NICER/LAXPC were consistent. The power density spectra from LAXPC and NICER revealed a broad, prominent feature at ∼2 Hz. The energy dependence of the fractional rms and time lag of this feature cannot be explained by only variations of coronal spectral parameters. Instead, a model where the coronal heating rate varies first and induces a change in the disk temperature and inner radius can explain the variation. Our results underline the importance of simultaneous observations by AstroSat and NICER and highlight the need for more sophisticated models to explain the spectral-temporal behavior of black hole systems.

Two Radio Cores in GPS J1543-0757: A New Dual Supermassive Black Hole System?

We report on the discovery of a dual supermassive black hole system in the radio galaxy J1543−0757, with a projected separation between the two black holes of ∼46 mas. The result is based on recent multifrequency observations using the Very Long Baseline Array and European VLBI Network, which reveal two compact, variable, flat-spectrum, active nuclei within the elliptical host galaxy of J1543−0757. Multiepoch observations from the Very Long Baseline Array also provide constraints on the spectral index and proper motions of all components. The flat spectra of both N and S at both frequencies strongly support the hypothesis that these radio components are associated with two separate, accreting supermassive black holes. The two nuclei appear stationary, while the jets emanating from the weaker of the two nuclei appear to move out and terminate in bright hotspots. The discovery of this system has implications for the number of close dual black holes that might be sources of gravitational radiation.

CFD Simulation of the Influence of the Type of Gas Distribution in the Burners on Thermal Aerodynamic Processes in the DKVR 10-13 Boiler

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power stations. However, in Asian countries, the ease of using natural gas as the main fuel and its environmental friendliness compared to coal made it possible to widely use natural gas in industry and energy sector. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion that it has the most attractive characteristics for its use in industry, including energy facilities, can be drawn. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy sector in the near future. The paper is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal one and at 60% capacity. The study was carried out using numerical methods with the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single-row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NOx generation in jet-niche systems was obtained. The authors of the paper believe that replacing the regular burners of the DKVR-10-13 water heating boiler with a jet-niche ones can contribute to better mixing of fuel and air and ensure more complete combustion. In this paper, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of combustion products spraying. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NOx. Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

Observations of fast radio variations in microquasars by FAST

Abstract Microquasars are the compact objects generally including accreting black holes which produce relativistic jets. The physical mechanisms of jet launching, collimation, and acceleration are poorly understood. Microquasars show strong variability in multi-wavelength observations. In X-rays, the sources show the fast variation features down to millisecond time scales, with the prominent quasiperiodic oscillations (QPOs) around 0.1 Hz - tens of Hz in light curves, however, physical origin of QPOs is still uncertain. FAST as the largest radio telescope provides the opportunity to study fast variability of both radio flux and polarization in microquasars. In the FAST observations from 2020 - 2022, we reported the first evidence of radio subsecond quasi-periodic oscillations of GRS 1915+105, providing the direct link between QPOs and the dynamics of relativistic jets. These QPOs with the centroid frequency around 5 Hz are transient, accompanied with strong evolution of the spectral index. Combined with multiwavelength observations, we discuss the possible physical models to produce radio QPOs in BH systems: the helical motion of jet knots or precession of the jet base. In near future, high time resolution radio monitoring of microquasars based on FAST is expected to discover more new phenomena in black hole systems, which will be important to understand the physics in strong gravity.

Modeling of thermo-aerodynamic and environmental parameters on the example of a two-pipe water heating boiler that has worked out the park resource

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power station. However, in Asian countries, the ease of using natural gas in industry as the main fuel, its environmental friendliness compared to coal, made it possible to widely use natural gas in industry and energy. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion can be drawn that it has the most attractive characteristics for its use in industry, including energy. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy industry in the near future. The presented work is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal and at 60% capacity. The study was carried out using numerical methods using the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single- row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NO x generation in SNS was obtained. In this work, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of spraying of combustion products. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NO x . Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

Explanation of puzzling FQHE at the filling fraction 3/4 in a band-hole 2D system in GaAs

A recent experiment revealed an unexpected FQHE at filling fraction 3/4 in a GaAs 2D hole system, which contradicts the composite fermion model prediction and the observation of a compressible Hall metal-type state in a twin 2D electron system in GaAs at the same filling fraction 3/4 at almost same other conditions. This finding challenges conventional effective single-quasiparticle model for FQHE exposing its limitations. We explain this experimental observation within a multiparticle approach based on a topological cyclotron commensurability criterion. This allows to generalize Laughlin function for filling fractions from the complete FQHE hierarchy including observable FQHE states at even denominator fractions. The topological multiparticle approach helps to decipher a structure of composite fermions and provides their generalization for so-called enigmatic states including even denominator filling fractions, and also for quantum fractional Hall-type behavior in Chern topological insulators without a magnetic field.

Detection of the Fe K lines from the binary AGN in 4C+37.11

We report the discovery of the Fe K line emission at $ $ keV with a width of $ $ keV using two epochs of Chandra archival data for the nucleus of the galaxy 4C+37.11, which is known to host a binary supermassive black hole (BSMBH) system where the SMBHs are separated by $ mas or sim 7pc. Our study reports the first detection of the Fe K line from a known binary AGN, which has an F-statistic value of 20.98 and a probability of $2.47 $. Stacking two spectra reveals another Fe K line component at $ $ keV. Different model scenarios indicate that the lines originate from the combined effects of accretion disk emission and circumnuclear collisionally ionized medium. The observed low column density favors a gas-poor merger scenario, where the high temperature of the hot ionized medium may be associated with the shocked gas in the binary merger and not with star formation activity. The estimated total BSMBH mass and disk inclination are $ $ M$_ and $ indicating that the BSMBH is probably a high-inclination system. We were not able to tightly constrain the spin parameter using the present data sets. Our results draw attention to the fact that detecting the Fe K line emissions from BSMBHs is important for estimating the individual SMBH masses and the spins of the binary SMBHs, as well as for exploring their emission regions.

Relaxation rate of ModMax–de Sitter black holes perturbed by massless neutral scalar fields

In this study, we investigate the behavior of ModMax-de Sitter black holes when perturbed by massless neutral scalar fields. Specifically, we analyze how the relaxation time, defined as the inverse of the fundamental imaginary frequency, varies with respect to two key parameters: the cosmological constant and the nonlinear parameter characterizing the ModMax theory. We explore scenarios both with and without a cosmological constant, focusing on the static charged ModMax black hole configuration. Our results reveal dependencies between the relaxation time and the nonlinear parameter, shedding light on the dynamical properties of these black hole systems. We also show the validity of WKB approximation under consideration.

Probing general relativistic spin–orbit coupling with gravitational waves from hierarchical triple systems

ABSTRACT Wave packets propagating in inhomogeneous media experience a coupling between internal and external degrees of freedom and, as a consequence, follow spin-dependent trajectories. These phenomena, well known in optics and condensed matter physics, are referred to as spin Hall effects. Similarly, the gravitational spin Hall effect is expected to affect the propagation of gravitational waves on curved spacetimes. In this general-relativistic setup, the curvature of spacetime acts as impurities in a semiconductor or inhomogeneities in an optical medium, leading to a frequency- and polarization-dependent propagation of wave packets. In this letter, we study this effect for strong-field lensed gravitational waves generated in hierarchical triple black hole systems in which a stellar-mass binary merges near a more massive black hole. We calculate how the gravitational spin Hall effect modifies the gravitational waveforms and show its potential for experimental observation. If detected, these effects will have profound implications for astrophysics and tests of general relativity.

Stabilizing effects of higher-order quantum corrections on charged BTZ black hole thermodynamics

In this paper, we study the thermodynamic properties and stability of static charged BTZ black holes with the inclusion of higher-order quantum corrections. The corrections to the entropy, mass, and Helmholtz free energy are derived, revealing the intricate interplay between quantum effects and classical gravitational forces in the context of black hole thermodynamics. The study of the specific heat capacity shows that higher-order corrections stabilize the system by removing the instabilities present at lower orders. The analysis of the van der Waals-like isotherms demonstrates the continuous transition from a highly compressible to an almost incompressible regime as the volume is decreased, akin to the behavior of supercritical fluids. Notably, the isotherms do not exhibit any regions of negative compressibility, indicating the absence of instabilities. Furthermore, the convexity of the Helmholtz free energy as a function of volume confirms the stability of the charged BTZ black hole system. These findings provide valuable insights into the complex thermodynamic landscape of three-dimensional black holes and the role of quantum corrections in shaping their behavior.

Stability Analysis of Stable Circular Orbit in Multi-Static Black Hole Spacetime

We herein study the circular orbit stability of a static black hole system composed of multiple Reissner–Nordstrom (RN) black holes. By comparing the circular orbits of two static black holes, three static black holes (TBHs), four static black holes and five static black holes at different spacetime, we find that the continuity of their stable circular orbits changes, i.e., the peaks of the effective potentials are transformed from single-peaked to bi-peaked, and that the distance a between the black holes is the main reason for this change. This characteristic is completely different from the continuity of the stable circular orbit interval of any kind of single black hole in the past. After calculation, we obtain several critical values that lead to the change in circular orbit stability. The three fundamental frequencies (orbital frequency, radial local frequency, and vertical local frequency) are derived and compared for two different spacetimes of double and three black holes. We also analyse the effect of the black hole distance a on the three fundamental frequencies of circular orbits.

Topology of charged AdS black hole in restricted phase space* *Supported by the National Natural Science Foundation of China (12075143, 12375050), and the Natural Science Foundation of Shanxi Province, China (202203021221209, 202303021211180)

The local topological properties of black hole systems can be expressed through winding numbers as defects. To date, AdS black hole thermodynamics are often depicted by the dual parameters of in the extended phase space, while there have been several studies on the black hole thermodynamics in the restricted phase space. In this paper, we analyze the topological properties of charged AdS black holes in the restricted phase space under the higher-dimension and higher-order curvature gravity frame. The results show that the topological number of the charged black hole in the same canonical ensembles is a constant and is independent of the concrete dual thermodynamical parameters. However, the topological number in the grand canonical ensemble is different from that in the canonical ensemble for the same black hole system. Furthermore, these results are independent of dimension d and highest order k of the Lanczos-Lovelock densities.

Resolving a Candidate Dual Active Galactic Nucleus with ∼100 pc Separation in MCG-03-34-64

We report the serendipitous multiwavelength discovery of a candidate dual black hole system with a separation of ∼100 pc, in the gas-rich luminous infrared galaxy MCG-03-34-64 (z = 0.016). Hubble Space Telescope/Advanced Camera for Surveys observations show three distinct optical centroids in the [O iii] narrow-band and F814W images. Subsequent analysis of Chandra/ACIS data shows two spatially resolved peaks of equal intensity in the neutral Fe Kα (6.2–6.6 keV) band, while high-resolution radio continuum observations with the Very Large Array at 8.46 GHz (3.6 cm band) show two spatially coincident radio peaks. Fast shocks as the ionizing source seem unlikely, given the energies required for the production of Fe Kα. If confirmed, the separation of ∼100 pc would represent the closest dual active galactic nuclei reported to date with spatially resolved, multiwavelength observations.

Eccentricity Estimation for Five Binary Black Hole Mergers with Higher-order Gravitational-wave Modes

The detection of orbital eccentricity for a binary black hole system via gravitational waves is a key signature to distinguish between the possible binary origins. The identification of eccentricity has been difficult so far due to the limited availability of eccentric gravitational waveforms over the full range of black hole masses and eccentricities. Here we evaluate the eccentricity of five black hole mergers detected by the LIGO and Virgo observatories using the TEOBResumS-DALI, TEOBResumS-GIOTTO, and TEOBResumSP models. This analysis studies eccentricities up to 0.6 at the reference frequency of 5 Hz and incorporates higher-order gravitational-wave modes critical to model emission from highly eccentric orbits. The binaries have been selected due to previous hints of eccentricity or due to their unusual mass and spin. While other studies found marginal evidence for eccentricity for some of these events, our analyses do not favor the incorporation of eccentricity compared to the quasi-circular case. While lacking the eccentric evidence of other analyses, we find our analyses marginally shifts the posterior in multiple parameters for several events when allowing eccentricity to be nonzero.

Merging hierarchical triple black hole systems with intermediate-mass black holes in population III star clusters

ABSTRACT Theoretical predictions suggest that very massive stars have the potential to form through multiple collisions and eventually evolve into intermediate-mass black holes (IMBHs) within Population III star clusters embedded in mini dark matter haloes. In this study, we investigate the long-term evolution of Population III star clusters, including models with a primordial binary fraction of $f_{\rm b}=0$ and 1, using the N-body simulation code petar. We comprehensively examine the phenomenon of hierarchical triple black holes in the clusters, specifically focusing on their merging inner binary black holes (BBHs), with post-Newtonian correction, by using the tsunami code. Our findings suggest a high likelihood of the inner BBHs containing IMBHs with masses on the order of $\mathcal {O}(100)\,{\rm M}_{\odot }$, and as a result, their merger rate could be up to $0.1{\rm Gpc}^{-3}{\rm yr}^{-3}$. The orbital eccentricities of some merging inner BBHs oscillate over time periodically, known as the Kozai–Lidov oscillation, due to dynamical perturbations. Detectable merging inner BBHs for mHz GW detectors LISA/TianQin/Taiji concentrate within $z\lt 3$. More distant sources would be detectable for CE/ET/LIGO/KAGRA/DECIGO, which are sensitive from $\mathcal {O}(0.1)$Hz to $\mathcal {O}(100)$ Hz. Furthermore, compared with merging isolated BBHs, merging inner BBHs affected by dynamical perturbations from tertiary BHs tend to have higher eccentricities, with a significant fraction of sources with eccentricities closing to 1 at mHz bands. GW observations would help constrain the formation channels of merging BBHs, whether through isolated evolution or dynamical interaction, by examining eccentricities.