Black Hole Potential Research Articles

Echoes from charged black holes influenced by quintessence

In this paper, we investigate the effective potential and echoes from dyonic black holes with quintessence. For a dyonic black hole, the quasi-topological electromagnetism provides proper matter energy–momentum tensor to curve the spacetime, and quintessence strengthens this force. We find that when the effect of quintessence becomes stronger, the black hole potential will experience a series of complex transition processes between single-peak and double-peak. This causes repeated appearance and disappearance of the black hole echoes. In particular, we find that observer will receive a sudden vanishment of high-frequency echoes when quintessence remains a relatively strong effect.

Greybody factors for massive scalar field emitted from black holes in dRGT massive gravity

Greybody factors are transmission probabilities of the Hawking radiation, which are emitted from black holes and can be obtained from the gravitational potential of black holes. The de Rham, Gabadadze, and Tolly (dRGT) massive gravity is one of the gravity theories that modified general relativity. In this paper, we investigate the greybody factor from the massive scalar field in both the asymptotically dS and the AdS spacetime using the WKB and the rigorous bound methods. We found that the greybody factor depends on the shape of the potential as found in quantum mechanics. The higher the potential barrier, the lower the amount of the greybody factor. Interestingly, for the low multipole case, we found that there exists a critical mass which provides the maximum bound of the greybody factor. This is a crucial feature of the massive scalar field on the greybody factor from the black holes in both the asymptotically dS and the AdS spacetime.

Tidal Disruption of Stellar Clusters and the Spatial Distribution of Their Remnants Near the Galactic Center

The accretion of massive star clusters via dynamical friction has previously been established to be a likely scenario for the buildup of nuclear stellar clusters (NSCs). A remaining issue is whether strong external tidal perturbation may lead to the severe disruption of loosely bound clusters well before they sink deeply into the center of their host galaxies. We carry out a series of N-body simulations and verify our early idealized analytic models. We show that if the density profile of the host galaxies can be described by a power-law distribution with an index of α < 1, the cluster would be compressed in the radial direction by the external galactic tidal field. In contrast, the galactic tidal perturbation is disruptive in regions with a steep, α > 1, density falloff or in the very center where gravity is dominated by the point-mass potential of supermassive black holes (SMBHs). This sufficient criterion supplements the conventional necessary Roche-lobe-filling condition in determining the preservation versus disintegration of satellite stellar systems. We simulate the disruption of stellar clusters that venture onto nearly circular, modestly, or highly eccentric orbits into the center of galaxies with a range of background density profiles and SMBHs. We obtain the spatial distribution of the stellar cluster remnants. We apply these results to the NSC within a few parsecs from SMBH Sgr A* at the Galactic Center. Recent observations indicate the coexistence of two populations of stars with distinctively separate ages and metallicities. We verify that the subsolar-metallicity population can be the debris of disrupted stellar clusters.

Study of photon orbit around magnetic black holes coupled to nonlinear electrodynamics

In this work we study the orbit of light particles around a asymptotically at, magnetically charged black hole which is coupled to a model of nonlinear form of Maxwell electrodynamics. The matter source is characterized by two parameters, β and γ, which determine the behaviour of photon around the corresponding spacetime. We serve the effective potential and analyse its change by varying the charge and the model parameter. Finally, we solve its orbit equation and show how photon moves according to the black hole potential.

Large-scale dynamics of winds driven by line force from a thin accretion disc

ABSTRACT Winds play a significant role in active galactic nuclei feedback process. Previous simulations studying winds only focus on a small dynamical range. Therefore, it is unknown how far the winds can go and what the properties of the winds will be if they can move to large radii. We perform simulations to study the large-scale dynamics of winds driven by line force. We find that the properties of the winds depend on both black hole mass (MBH) and accretion disc luminosity. When the accretion disc luminosity is 0.6Ledd (Ledd being Eddington luminosity), independent of MBH, the winds have kinetic energy flux exceeding $1{{\ \rm per\ cent}} L_{\rm edd}$ and can escape from the black hole potential. For the case with the accretion disc luminosity equaling 0.3 Ledd, the strength of the winds decreases with the decrease of MBH. If MBH decreases from 109 to 106 solar mass (M⊙), the winds kinetic energy flux decreases from ∼0.01 Ledd to ∼10−6Ledd. In case of $M_{\rm BH}\ge 10^7 \, \mathrm{M}_\odot$, winds can escape from black hole potential. In the case of $M_{\rm BH}=10^6 \, \mathrm{M}_\odot$, the winds cannot escape. We find that for the ultra-fast winds observed in hard X-ray bands, the observed dependence of the mass flux and the kinetic energy flux on accretion disc luminosity can be well produced by line force driven winds model. We also find that the properties of the ultra-fast winds observed in soft X-ray bands can be explained by the line force driven winds model.

Black hole attractors and U(1) Fayet-Iliopoulos gaugings: analysis and classification

We classify the critical points of the effective black hole potential which governs the attractor mechanism taking place at the horizon of static dyonic extremal black holes in mathcal{N} = 2, D = 4 Maxwell-Einstein supergravity with U(1) Fayet-Iliopoulos gaugings. We use a manifestly symplectic covariant formalism, and we consider both spherical and hyperbolic horizons, recognizing the relevant sub-classes to which some representative examples belong. We also exploit projective special Kähler geometry of vector multiplets scalar manifolds, the U-duality-invariant quartic structure (and 2-polarizations thereof) in order to retrieve and generalize various expressions of the entropy of asymptotically AdS4 BPS black holes, in the cases in which the scalar manifolds are symmetric spaces. Finally, we present a novel static extremal black hole solution to the STU model, in which the dilaton interpolates between an hyperbolic near-horizon geometry and AdS4 at infinity.

Molecular gas dynamics around nuclei of galaxies

Recent molecular line observations with ALMA in several nearby Seyferts have revealed the existence of molecular tori, and the nature of gas flows at 10-20 pc scale. At 100 pc scale, or kpc-scale, previous NOEMA work on gravitational torques had shown that only about one third of Seyfert galaxies experienced molecular inflow and central fueling, while in most cases the gas was stalled in rings. At higher resolution, i.e. 10-20 pc scale, it is possible now to see in some cases AGN fueling due to nuclear trailing spirals, influenced by the black hole potential. This brings smoking gun evidence for nuclear fueling. In our sample galaxies, the angular resolution of up to 60 mas allows us to reach the black hole (BH) sphere of influence and the BH mass can be derived more directly than with the M-sigma relation.

Tidal Disruptions of Main-sequence Stars. III. Stellar Mass Dependence of the Character of Partial Disruptions

Abstract In this paper, the third in this series, we continue our study of tidal disruption events of main-sequence stars by a nonspinning 106 M ⊙ supermassive black hole. Here we focus on the stellar mass dependence of the outcomes of partial disruptions. As the encounter becomes weaker, the debris mass is increasingly concentrated near the outer edges of the energy distribution. As a result, the mass fallback rate can deviate substantially from a t −5/3 power law, becoming more like a single peak with a tail declining as t −p with p ≃ 2–5. Surviving remnants are spun-up in the prograde direction and are hotter than main-sequence stars of the same mass. Their specific orbital energy is ≃10−3× that of the debris, but of either sign with respect to the black hole potential, while their specific angular momentum is close to that of the original star. Even for strong encounters, remnants have speeds at infinity relative to the black hole potential ≲300 km s−1, so they are unable to travel far out into the galactic bulge. The remnants most deeply bound to the black hole go through a second tidal disruption event upon their first return to pericenter; if they have not thermally relaxed, they will be completely disrupted.

Large-scale Dynamics of Winds Originating from Black Hole Accretion Flows. I. Hydrodynamics

Abstract Winds from black hole accretion flows are ubiquitous. Previous works mainly focus on the launching of wind on the accretion flow scale. It still remains unclear how far the winds can propagate outward and what their large-scale dynamics is. As the first paper of this series, we study the large-scale dynamics of thermal wind beyond accretion scales via analytical and numerical methods. Boundary conditions, which are crucial to our problem, are analyzed and presented based on small-scale simulations combined with observations of winds. Both black hole and galaxy potential are taken into account. For winds originating from hot accretion flows, we find that the wind can reach large scales. The radial profiles of velocity, density, and temperature can be approximated by and , where v r0, ρ 0, and T 0 are the velocity, density, and temperature of winds at the boundary , and γ is the polytropic index. During the outward propagation, the enthalpy and rotational energy compensate for the increase of gravitational potential. For thin disks, we find that because the Bernoulli parameter is smaller, winds cannot propagate as far as the hot winds, but stop at a certain radius where the Bernoulli parameter is equal to the potential energy. Before the winds stop, the profiles of dynamical quantities can also be approximated by the above relations. In this case, the rotational energy alone compensates for the increase in potential energy.

Secular evolution and pseudo-bulges

AbstractThrough vertical resonances, bars can produce pseudo-bulges, within secular evolution. Bulges and pseudo-bulges have doubled their mass since z=1. The frequency of bulge-less galaxies at z=0 is difficult to explain, especially since clumpy galaxies at high z should create classical bulges in all galaxies. This issue is solved in modified gravity models. Bars and spirals in a galaxy disk, produce gravity torques that drive the gas to the center and fuel central star formation and nuclear activity. At 0.1-1kpc scale, observations of gravity torques show that only about one third of Seyfert galaxies experience molecular inflow and central fueling, while in most cases the gas is stalled in resonant rings. At 10-20pc scale, some galaxies have clearly revealed AGN fueling due to nuclear trailing spirals, influenced by the black hole potential. Thanks to ALMA, and angular resolution of up to 80mas, it is possible to reach the central black hole (BH) zone of influence, discover molecular tori, circum-nuclear disks misaligned with the galaxy, and the BH mass can be derived more directly from the kinematics.

Inverse problem for Hawking radiation

In this work we study the inverse problem related to the emission of Hawking radiation. We first show how the knowledge of greybody factors of different angular contributions $l$ can be used to constrain the width of the corresponding black hole perturbation potentials. Afterwards we provide a framework to recover the greybody factors from the actual energy emission spectrum, which has to be treated as sum over all multipole numbers. The underlying method for the reconstruction of the potential widths is based on the inversion of the Gamow formula, a parabolic expansion and the P\"oschl-Teller potential. We define a `normalized' energy emission spectrum that turns out to be very beneficial for the numerical fitting process, as well as for an improved qualitative understanding of how much information of the black hole potentials are actually imprinted in the spectrum. The connection to recent studies on the inverse problem using the quasi-normal spectra of ultra compact stars and exotic compact objects is discussed as well. In the appendix we show that the spectrum can be approximated surprisingly well and simply with a parabolic expansion of the peak of the classical black hole scattering potentials.

Low angular momentum accretion of fractal medium on to Kerr black holes and the emergence of the acoustic manifold

For three different geometric configurations of matter and two different thermodynamic equations of state, low angular momentum, multi-transonic, axially symmetric accretion flow of matter having fractional dimension of mass distribution onto a rotating black hole has been studied by employing certain post-Newtonian pseudo-Kerr black hole potential. Such task has been accomplished mathematically by mapping the fractal nature of accreted medium onto its continuum counterpart. The difference between spin dependence of accretion dynamics of the fractal medium and the continuous medium has been highlighted. By employing a time dependent linear perturbation scheme, it has been demonstrated that accretion of matter with fractional dimension of density distribution can be considered as a natural example of classical analogue model. The corresponding acoustic surface gravity has been estimated in terms of accretion variables. The value of the surface gravity changes as the accreted matter makes a transition from its fractal nature to the corresponding continuum distribution.

Quasinormal modes of gravitational perturbation around regular Bardeen black hole surrounded by quintessence

In this paper, Quasinormal modes of gravitational perturbation are investigated for the regular Bardeen black hole surrounded by quintessence. Considering the metric of the Bardeen spacetime surrounded by quintessence, we derived the perturbation equation for gravitational perturbation using Regge-Wheeler gauge. The third order Wentzel-Kramers-Brillouin (WKB) approximation method is used to evaluate quasinormal frequencies. Explicitly, the behaviors of the black hole potential and quasinormal modes were plotted. The results show that, due to the presence of quintessence, the gravitational perturbation around the black hole damps more slowly and oscillates more slowly.

Thermodynamics of charged dilatonic BTZ black holes in rainbow gravity

In this paper, the charged three-dimensional Einstein's theory coupled to a dilatonic field has been considered in the rainbow gravity. The dilatonic potential has been written as the linear combination of two Liouville-type potentials. Four new classes of charged dilatonic rainbow black hole solutions, as the exact solution to the coupled field equations of the energy dependent space time, have been obtained. Two of them are correspond to the Coulomb's electric field and the others are consequences of a modified Coulomb's law. Total charge and mass as well as the entropy, temperature and electric potential of the new charged black holes have been calculated in the presence of rainbow functions. Although the thermodynamic quantities are affected by the rainbow functions, it has been found that the first law of black hole thermodynamics is still valid for all of the new black hole solutions. At the final stage, making use of the canonical ensemble method and regarding the black hole heat capacity, the thermal stability or phase transition of the new rainbow black hole solutions have been analyzed.

Scattering of Ricci scalar perturbations from Schwarzschild black holes in modified gravity

It has already been shown that the gravitational waves emitted from a Schwarzschild black hole in f(R) gravity have no signatures of the modification of gravity from General Relativity, as the Regge–Wheeler equation remains invariant. In this paper we consider the perturbations of Ricci scalar in a vacuum Schwarzschild spacetime, which is unique to higher order theories of gravity and is absent in General Relativity. We show that the equation that governs these perturbations can be reduced to a Volterra integral equation. We explicitly calculate the reflection coefficients for the Ricci scalar perturbations, when they are scattered by the black hole potential barrier. Our analysis shows that a larger fraction of these Ricci scalar waves are reflected compared to the gravitational waves. This may provide a novel observational signature for fourth order gravity.

Influence of the black hole spin on the chaotic particle dynamics within a dipolar halo

We investigate the role of the spin angular momentum of astrophysical black holes in controlling the special relativistic chaotic dynamics of test particles moving under the influence of a post-Newtonian pseudo-Kerr black hole potential, along with a perturbative potential created by a asymmetrically placed (dipolar) halo. Proposing a Lyapunov-like exponent to be the effective measure of the degree of chaos observed in the system under consideration, it has been found that black hole spin anti-correlates with the degree of chaos for the aforementioned dynamics. Our findings have been explained applying the general principles of dynamical systems analysis.

MAGNETOHYDRODYNAMIC NUMERICAL SIMULATION OF WIND PRODUCTION FROM HOT ACCRETION FLOWS AROUND BLACK HOLES AT VERY LARGE RADII

ABSTRACT Numerical simulations of hot accretion flows around black holes have shown the existence of strong wind. Those works focused only on the region close to the black hole and thus it is unknown whether or where the wind production stops at large radii. To address this question, we have recently performed hydrodynamic (HD) simulations by taking into account the gravitational potential of both the black hole and the nuclear star cluster. The latter is assumed to be proportional to , with σ being the velocity dispersion of stars and r the distance from the center of the galaxy. It was found that when the gravity is dominated by nuclear stars, i.e., outside a radius , winds can no longer be produced. That work, however, neglects the magnetic field, which is believed to play a crucial dynamical role in the accretion and thus must be taken into account. In this paper, we revisit this problem by performing magnetohydrodynamic (MHD) simulations. We confirm the result of our previous paper, namely that wind cannot be produced in the region . Our result, combined with recent results of Yuan et al., indicates that the formula describing the mass flux of wind, , can only be applied to the region where the black hole potential is dominant. Here is the mass accretion rate at the black hole horizon and the value of R A is similar to the Bondi radius.

Mayer's Formula for Black Hole Thermodynamics in Constant Magnetic Field

Using the concepts of the classical thermodynamics, we calculated in this work, the thermodynamic potential of black holes in the presence of a constant externel magnetic field present in the surrounding black hole. This calculation takes into account the developments previously provided by (Hawking, Bekenstein, Davies and Straumann) on the equations governing the dynamics of black holes,with an arbitrary value of the surface gravity k. Like the four classical thermodynamic Maxwell equations, we have developed, for black holes, new twenty four fundamental equations. Among these equations, particular attention was given to the calculation of specific heats CΩ,Φ,M and CJ,Q,B and the Mayer formula for a black hole in the presence of magnetic field.

Regular black holes in de Sitter universe: Scalar field perturbations and quasinormal modes

The purpose of this paper is to study quasinormal modes (QNMs) of a regular black hole with a cosmological constant due to scalar perturbations. A detailed study of QNMs frequencies for the massless scalar field was done by varying the parameters of the theory such as mass, magnetic charge, cosmological constant and the spherical harmonic index. We have employed the sixth-order WKB approximation to compute the QNMs frequencies. We have also proved analytically that the [Formula: see text] mode for the massless field reaches a constant value at late times. We have approximated the near-extreme regular-de Sitter (dS) black hole potential with the Pöschl–Teller potential to obtain exact frequencies. The null geodesics of the regular-de Sitter black hole is employed to describe the QNMs frequencies at the eikonal limit ([Formula: see text]).

An approach to the quantization of black hole quasi-normal modes

In this work, we derive the asymptotic quasi-normal modes of a Banados–Teitelboim–Zanelli (BTZ) black hole using a quantum field theoretic Lagrangian. The BTZ black hole is a very popular system in the context of 2 + 1-dimensional quantum gravity. However, to our knowledge the quasi-normal modes of the BTZ black hole have been studied only in the classical domain. Here we show a way to quantize the quasi-normal modes of the BTZ black hole by mapping it to the Bateman–Feschbach–Tikochinsky oscillator and the Caldirola–Kanai oscillator. We have also discussed a couple of other black hole potentials to which this method can be applied.