Presence Of Black Hole Research Articles

Scattering of massless scalar field by charged dilatonic black holes

Wave propagations in the presence of black holes is a significant problem both in theoretical and observational aspects, especially after the discovery of gravitational wave and confirmation of black holes. We study the scattering of massless scalar field by a charged dilatonic black hole in frame of full wave theory. We apply partial wave method to obtain the scattering cross sections of the scalar field, and investigate how the black hole charge affects the scalar scattering cross sections. Furthermore, we investigate the Regge pole approach of the scattering cross section of the dilatonic black hole. We find that in order to obtain results at the same precision, we need more Regge poles as the black hole charge increases. We compare the results in the full wave theory and results in the classical geodesic scattering and the semi-classical glory approximations, and demonstrate the improvements and power of our approach.

Diagnostic revisions in multiple sclerosis

AbstractObjectivesThe diagnostic criteria for inflammatory demyelinating diseases of the central nervous system have evolved over the past years. Close follow up and accurate multiple sclerosis (MS) diagnosis are key to optimal treatment. We retrospectively reviewed the patients who had a diagnostic revision.MethodsThe medical records of patients referred to our MS clinic (Centro Hospitalar Universitário de São João, Porto, Portugal) (n = 635) between 2009 and 2016 were reviewed. A total of 62 patients were identified, 44 were misdiagnosed with MS; 18 had another diagnosis, later redefined as MS. A total of 44 controls (with MS diagnosis) were matched to the 44 misdiagnosed cases, and a statistical analysis was carried out to determine the predictors of misdiagnosis.ResultsThe mean age of our population (n = 44) was 51 ± 11 years; 77% were women. The mean duration of misdiagnosis was 13 years. Optic neuritis was the most frequent presenting symptom (25%), followed by spinal cord syndrome and non‐specific neurological symptoms (20% each). The most frequent MS misdiagnoses were non‐specific white matter hyperintensities, optic neuritis and cerebrovascular disease. The mean Extended Disability Status Scale and Multiple Sclerosis Severity Score was 0 (SD 2) and 0.6 (SD 2), respectively, in the misdiagnosed group, and 3.5 (SD 5.4) and 3.2 (SD 5.6), respectively, in the control group. From all the variables analyzed, we found that the presence of black holes and spinal cord lesions were predictors of a correct MS diagnosis (P < 0,05).ConclusionsOur series underlines the need to continuously rethink an MS diagnosis and to thoughtfully use paraclinical tests (oligoclonal bands and magnetic resonance imaging) avoiding an unfounded diagnosis. The first event might not be atypical, as has been reported in other series.

Is GW190425 Consistent with Being a Neutron Star–Black Hole Merger?

Abstract GW190425 is the second neutron star merger event detected by the Advanced LIGO/Virgo detectors. If interpreted as a double neutron star merger, the total gravitational mass is substantially larger than that of the binary systems identified in the Galaxy. In this work we analyze the gravitational-wave data within the neutron star–black hole merger scenario. For the black hole, we yield a mass of and an aligned spin of . As for the neutron star we find a mass of and the dimensionless tidal deformability of . These parameter ranges are for 90% credibility. The inferred masses of the neutron star and the black hole are not in tension with current observations and we suggest that GW190425 is a viable candidate of a neutron star–black hole merger event. Benefitting from the continual enhancement of the sensitivities of the advanced gravitational detectors and the increase of the number of the observatories, similar events are anticipated to be much more precisely measured in the future and the presence of black holes below the so-called mass gap will be unambiguously clarified. If confirmed, the mergers of neutron stars with (quickly rotating) low-mass black holes are likely important production sites of the heaviest r-process elements.

Thermodynamic phase transition for quintessence dyonic anti-de Sitter black holes

We study thermodynamic of a dyonic AdS black hole surrounded by quintessence dark energy where negative cosmological constant of AdS space behaves as pressure of the black hole. We choose grand canonical ensemble of the black hole where its magnetic charge $Q_M$ and electric potential $\Phi_E$ are hold as constant. Our goal in this work is study physical effects of the magnetic charge and electric potential on the thermodynamic phase transition of the black hole in presence of quintessence dark energy. When barotropic index of the quintessence is $\omega=-\frac{7}{9}$ we obtained that compressibility factor of the black hole reduces to $Z_c=\frac{3}{8}$ which corresponds to the Van der Waals fluid. We obtained analogy between the small/large black hole phase transition and liquid/gas phase transition of the Van der Waals fluid. Numerical calculations predict that the black hole may born $plasma$ phase which is fourth different state of the matter which does not appear in the Van der Waals fluid.

Constraining the Black Hole Initial Mass Function with LIGO/Virgo Observations

Abstract Prior to the detection of black holes (BHs) via the gravitational waves (GWs) that they generate at merger, the presence of BHs was inferred in X-ray binaries, mostly via dynamical measurements, with masses in the range between ∼5 and 20 M ⊙. The Laser Interferometer Gravitational-Wave Observatory (LIGO) discovery of the first BHs via GWs was surprising in that the two BHs that merged had masses of and , which are both above the range inferred from X-ray binaries. With 20 BH detections from the first/second observing (O1/O2) runs, the distribution of masses remains generally higher than the X-ray inferred one, while the effective spins are generally lower. This suggests that, at least in part, the GW-detected population might be of dynamical origin rather than produced by the common evolution of field binaries. Here we perform high-resolution N-body simulations of a cluster of isolated BHs with a range of initial mass spectra and upper mass cutoffs, and study the resulting binary mass spectrum resulting from the dynamical interactions. Our clusters have properties that are similar to those of the massive remnants in an OB association ∼10 Myr after formation. We perform a likelihood analysis for each of our dynamically formed binary population against the data from the O1 and O2 LIGO/Virgo runs. We find that an initial mass spectrum M BH ∝ M −2.35 with an upper mass cutoff M max ∼ 50M ⊙ is favored by the data, together with a slight preference for a merger rate that increases with redshift.

Black holes in presence of cosmological constant: second order in frac{1}{D}

We have extended the results of [1] upto second subleading order in an expansion around large dimension D. Unlike the previous case, there are non-trivial metric corrections at this order. Due to our ‘background-covariant’ formalism, the dependence on Ricci and the Riemann curvature tensor of the background is manifest here. The gravity system is dual to a dynamical membrane coupled with a velocity field. The dual membrane is embedded in some smooth background geometry that also satisfies the Einstein equation in presence of cosmological constant. We explicitly computed the corrections to the equation governing the membrane-dynamics. Our results match with earlier derivations in appropriate limits. We calculated the spectrum of QNM from our membrane equations and matched them against similar results derived from gravity.

Triage of 5 Noncontrast Computed Tomography Markers and Spot Sign for Outcome Prediction After Intracerebral Hemorrhage.

Background and Purpose- Besides the established spot sign (SS) in computed tomography angiography (CTA), there is growing evidence that different imaging markers in noncontrast CT offer great value for outcome prediction in patients with intracerebral hemorrhage (ICH). However, it is unclear how the concurrent presence of each sign independently contributes to the predictive power of poor outcome. We, therefore, aimed to clarify the predictive value of 5 recently published noncontrast CT parameters (blend sign, black hole sign, island sign, hematoma heterogeneity, and hypodensities) and the established SS in 1 consecutive series of patients with ICH. Methods- Retrospective study of patients with ICH at 2 German tertiary stroke centers; inclusion criteria were (1) spontaneous ICH and (2) noncontrast CT and CTA performed on admission within 6 hours after onset of symptoms. We defined a binary outcome (good outcome [modified Rankin Scale score of ≤3] versus poor outcome [modified Rankin Scale score of >3]) at discharge. The predictive value of each sign was assessed in univariate and multivariable logistic regression models. Results- Of 201 patients with spontaneous ICH, 28 (13.9%) presented with black hole sign, 38 (18.9%) with blend sign, 120 (59.7%) with hypodensities, 97 (48.3%) with heterogeneous densities, 53 with island sign (26.4%), and 45 (22.4%) with SS. In univariable logistic regression, higher hematoma volume ( P<0.001), intraventricular hemorrhage ( P=0.002), and the presence of black hole sign/blend sign/hypodensities/island sign/SS/heterogeneous density (all P<0.001) on admission CT were associated with poor outcome. Multivariable analysis confirmed intraventricular hemorrhage (odds ratio, 2.20; P=0.025), higher hematoma volume (odds ratio, 1.02 per mL; P<0.019), the presence of hypodensities (odds ratio, 2.47; P=0.018), and SS (odds ratio, 12.22; P<0.001) as independent predictors of poor outcome. Conclusions- This study demonstrates the degree of interaction between 5 recent noncontrast CT imaging markers and SS and their individual contribution for outcome prediction in patients with ICH. Of the CT variables indicating poor outcome SS on CTA and hypodensities were the most reliable outcome predictors.

Standing shocks in magnetized advection accretion flows onto a rotating black hole

We present the global structure of magnetized advective accretion flow around the rotating black holes in presence of dissipation. By considering accretion flow to be threaded by toroidal magnetic fields and by assuming synchrotron radiative mechanism to be the dominant cooling process, we obtain global transonic accretion solutions in terms of dissipation parameters, such as viscosity ($\alpha_B$), accretion rate (${\dot m}$) and plasma-$\beta$, respectively. In the rotating magnetized accretion flow, centrifugal barrier is developed in the nearby region of the black hole that triggers the discontinuous shock transition in the flow variables. Evidently, the shock properties and the dynamics of the post-shock flow (hereafter post-shock corona (PSC)) are being governed by the flow parameters. We study the role of dissipation parameters in the formation of standing shock wave and find that global shocked accretion solutions exist both in gas pressure dominated flows and in magnetic pressure dominated flows. In addition, we observe that standing shock continues to form around the rapidly rotating black holes as well. We identify the range of dissipation parameters that permits shocked accretion solutions and find that standing shocks continue to form even in presence of high dissipation limit, although the likelihood of shock formation diminishes with the increase of dissipation. Further, we compute the critical accretion rate (${\dot m}^{\rm cri}$) that admits shock and observe that standing shock exists in a magnetically dominated accretion flow when the accretion rate lies in general in the sub-Eddington domain. At the end, we calculate the maximum dissipated energy that may be escaped from the PSC and indicate its possible implication in the astrophysical context.

Constraints on tidal charge of the supermassive black hole at the Galactic Center with trajectories of bright stars

As it was pointed out recently in Hees et al. (Phys Rev Lett 118:211101, 2017), observations of stars near the Galactic Center with current and future facilities provide an unique tool to test general relativity (GR) and alternative theories of gravity in a strong gravitational field regime. In particular, the authors showed that the Yukawa gravity could be constrained with Keck and TMT observations. Some time ago, Dadhich et al. (Phys Lett B 487:1, 2001) showed that the Reissner–Nordström metric with a tidal charge is naturally appeared in the framework of Randall–Sundrum model with an extra dimension (Q^2 is called tidal charge and it could be negative in such an approach). Astrophysical consequences of presence of black holes with a tidal charge are considerered, in particular, geodesics and shadows in Kerr–Newman braneworld metric are analyzed in Schee and Stuchlík (Intern J Mod Phys D 18:983, 2009), while profiles of emission lines generated by rings orbiting braneworld Kerr black hole are considered in Schee and Stuchlík (Gen Relat Grav 52:1795, 2009). Possible observational signatures of gravitational lensing in a presence of the Reissner–Nordström black hole with a tidal charge at the Galactic Center are discussed in papers (Bin-Nun in Phys Rev D 81:123011, 2010; Bin-Nun in Phys Rev D 82:064009, 2010; Bin-Nun in Class Quant Grav 28:114003, 2011). Here we are following such an approach and we obtain analytical expressions for orbital precession for Reissner–Nordström–de-Sitter solution in post-Newtonian approximation and discuss opportunities to constrain parameters of the metric from observations of bright stars with current and future astrometric observational facilities such as VLT, Keck, GRAVITY, E-ELT and TMT.

Security Against Network Layer Attacks for Hierarchal Mesh Environments

This article aims to secure a routing mechanism by completing amendments in previously proposed efficient secure routing (ESR) protocols against networking layer attacks in mesh networking environments. Along with generating the tickets to prove the authenticity of communicating clients, each node proves the legitimacy of its succeeding node by computing the behaviour. The intermediate nodes selected for routing the data packets proves the legitimacy of each other by getting the passive acknowledgement process within a predefined time to live (TTL) time. Further, grey hole and black hole attacks are considered in the network simulation environment as they drastically affect the network metrics during the communication because of their severe attacking characteristics. The proposed mechanism is validated over conventional routing mechanisms against packet loss and network delay parameters in the presence of black hole and grey hole routing attacks.

Advective accretion flow properties around rotating black holes – application to GRO J1655-40

We examine the properties of the viscous dissipative accretion flow around rotating black holes in presence of mass loss. Considering thin disc approximation, we self-consistently calculate the inflow-outflow solutions and observe that the mass outflow rates decreases with the increase of viscosity parameter ($\alpha$). Further, we carry out the model calculation of Quasi-periodic Oscillation frequency ($\nu_{\rm QPO}$) that is frequently observed in black hole sources and observe that $\nu^{\rm max}_{\rm QPO}$ increases with the increase of black hole spin ($a_k$). Then, we employ our model in order to explain the High Frequency Quasi-periodic Oscillations (HFQPOs) observed in black hole source GRO J1655-40. While doing this, we attempt to constrain the range of $a_k$ based on observed HFQPOs ($\sim$ 300 Hz and $\sim$ 450 Hz) for the black hole source GRO J1655-40.

Properties of two-temperature dissipative accretion flow around black holes

We study the properties of two-temperature accretion flow around a non-rotating black hole in presence of various dissipative processes where pseudo-Newtonian potential is adopted to mimic the effect of general relativity. The flow encounters energy loss by means of radiative processes acted on the electrons and at the same time, flow heats up as a consequence of viscous heating effective on ions. We assumed that the flow is exposed with the stochastic magnetic fields that leads to Synchrotron emission of electrons and these emissions are further strengthen by Compton scattering. We obtain the two-temperature global accretion solutions in terms of dissipation parameters, namely, viscosity (α) and accretion rate (⁠|${\dot{m}}$|⁠), and find for the first time in the literature that such solutions may contain standing shock waves. Solutions of this kind are multitransonic in nature, as they simultaneously pass through both inner critical point (xin) and outer critical point (xout) before crossing the black hole horizon. We calculate the properties of shock-induced global accretion solutions in terms of the flow parameters. We further show that two-temperature shocked accretion flow is not a discrete solution, instead such solution exists for wide range of flow parameters. We identify the effective domain of the parameter space for standing shock and observe that parameter space shrinks as the dissipation is increased. Since the post-shock region is hotter due to the effect of shock compression, it naturally emits hard X-rays, and therefore, the two-temperature shocked accretion solution has the potential to explain the spectral properties of the black hole sources.

An efficient approach to circumvent black hole nodes in manets

MANETs are self-configured network. Nodes in Manets need not follow a specific infrastructure. Nodes are connected wirelessly and so nodes can travel to any direction. Manets assure that all its nodes are cooperating with each other. Sometimes, some nodes may not be reliable. These unreliable intermediate nodes participate in the packet forwarding and drop the packets instead of forwarding them to the destination node. This type of security attack is called black hole attack (Baadache and Belmehdi in Int Comput Sci Inf Sec 7(1):1–10, 2010). In this paper, an efficient method of route discovery process is used which bypasses the black hole nodes and uses only the reliable route for transmission. The main advantage of using the proposed method is that there is no need to maintain black hole list. So, there is no need to check the black hole list each time during route discovery. Dynamic source routing (DSR) is used for the transmission of packets. The simulations are done to measure packet delivery ratio, packet drop, average throughput, normalized routing overhead and average end-to-end delay. Simulation results shows that the proposed method improves the packet delivery ratio in presence of black hole and reduces the packet drop. Also the communication overhead is reduced which in turn minimizes the resource utilization in Manets.

Detection of Enhanced Central Mass-to-light Ratios in Low-mass Early-type Galaxies: Evidence for Black Holes?

Abstract We present dynamical measurements of the central mass-to-light ratio (M/L) of a sample of 27 low-mass early-type galaxies. We consider all galaxies with 9.7 &lt; log( &lt; 10.5 in our analysis, selecting out galaxies with available high-resolution Hubble Space Telescope (HST) data, and eliminating galaxies with significant central color gradients or obvious dust features. We use the HST images to derive mass models for these galaxies and combine these with the central velocity dispersion values from data to obtain a central dynamical M/L estimate. These central dynamical are higher than dynamical derived at larger radii and stellar population estimates of the galaxy centers in ∼80% of galaxies, with a median enhancement of ∼14% and a statistical significance of 3.3σ. We show that the enhancement in the central M/L is best described either by the presence of black holes in these galaxies or by radial initial mass function variations. Assuming a black hole model, we derive black hole masses for the sample of galaxies. In two galaxies, NGC 4458 and NGC 4660, the data suggest significantly overmassive black holes, while in most others only upper limits are obtained. We also show that the level of M/L enhancements we see in these early-type galaxy nuclei are consistent with the larger enhancements seen in ultracompact dwarf galaxies (UCDs), supporting the scenario where massive UCDs are created by stripping galaxies of these masses.

An Upper Limit on the Mass of a Central Black Hole in the Large Magellanic Cloud from the Stellar Rotation Field

Abstract We constrain the possible presence of a central black hole (BH) in the center of the Large Magellanic Cloud. This requires spectroscopic measurements over an area of the order of a square degree, due to the poorly known position of the kinematic center. Such measurements are now possible with the impressive field of view of the Multi Unit Spectroscopic Explorer (MUSE) on the ESO Very Large Telescope. We used the Calcium Triplet (∼850 nm) spectral lines in many short-exposure MUSE pointings to create a two-dimensional integrated-light line-of-sight velocity map from the individual spectra, taking care to identify and remove Galactic foreground populations. The data reveal a clear velocity gradient at an unprecedented spatial resolution of 1 arcmin2. We fit kinematic models to arrive at a upper-mass limit of for any central BH—consistent with the known scaling relations for supermassive black holes and their host systems. This adds to the growing body of knowledge on the presence of BHs in low-mass and dwarf galaxies, and their scaling relations with host-galaxy properties, which can shed light on theories of BH growth and host system interaction.

Estimation of mass outflow rates from dissipative accretion disc around rotating black holes

We study the properties of the dissipative accretion flow around rotating black holes in presence of mass loss. We obtain the complete set of global inflow-outflow solutions in the steady state by solving the underlying conservation equations self-consistently. We observe that global inflow-outflow solutions are not the isolated solution, instead such solutions are possible for wide range of inflow parameters. Accordingly, we identify the boundary of the parameter space for outflows, spanned by the angular momentum ($\lambda_{\rm in}$) and the energy (${\cal E}_{\rm in}$) at the inner sonic point ($x_{\rm in}$), as function of the dissipation parameters and find that parameter space gradually shrinks with the increase of dissipation rates. Further, we examine the properties of the outflow rate $R_{\dot m}$ (defined as the ratio of outflow to inflow mass flux) and ascertain that dissipative processes play the decisive role in determining the outflow rates. We calculate the limits on the maximum outflow rate ($R_{\dot{m}}^{\rm max}$) in terms of viscosity parameter ($\alpha$) as well as black hole spin ($a_k$) and obtain the limiting range as $3\% \le R_{\dot{m}}^{\rm max} \le 19\%$. Moreover, we calculate the viable range of $\alpha$ that admits the coupled inflow-outflow solutions and find that $\alpha \lesssim 0.25$ for $R_{\dot m} \ne 0$. Finally, we discuss the observational implication of our formalism to infer the spin of the black holes. Towards this, considering the highest observed QPO frequency of black hole source GRO J1655-40 ($\sim 450$ Hz), we constrain the spin value of the source as $a_k \ge 0.57$.

Strong gravitational lensing—a probe for extra dimensions and Kalb-Ramond field

Strong field gravitational lensing in the context of both higher spacetime dimensions and in presence of Kalb-Ramond field have been studied. After developing proper analytical tools to analyze the problem we consider gravitational lensing in three distinct black hole spacetimes—(a) four dimensional black hole in presence of Kalb-Ramond field, (b) brane world black holes with Kalb-Ramond field and finally (c) black hole solution in f(T) gravity. In all the three situations we have depicted the behavior of three observables: the asymptotic position approached by the relativistic images, the angular separation and magnitude difference between the outermost images with others packed inner ones, both numerically and analytically. Difference between these scenarios have also been discussed along with possible observational signatures.

Search and study of objects of the early universe

The “Big Trio” program is conducted at the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) aiming to investigate a sample of sources with steep and ultra-steep spectra fromthe RCcatalog obtained on the basis of observational data of the “Cold” survey. The population of distant FRII type radio galaxies with steep spectra is of particular interest, since new data indicate the presence of black holes with masses of more than 109 M ⊙ which already formed in these giant stellar systems in the first billion years of life of the Universe, as well as their connection with emerging clusters. There are three sources with z sp > 3 in the sample. According to the observations of the 6-m SAO RAS telescope, the archival data of Subaru and Spitzer, an increased density of objects and several Lyα-emitters have been detected near one of the most powerful radio galaxies, RCJ0311+0507 (4C+04.11) with z = 4.51, which is the second most distant of the known FRII-type galaxies. Another object— RCJ1740+0502 with z = 3.57, is a possible dual AGN candidate. The third source, RCJ0105+0501, is an FRII-type galaxy (z = 3.138) with a host galaxy of a complex structure, possibly generated by interaction in a close pair of galaxies. These radio sources have high radio luminosity (L 500MHz ≈ 1028–1029WHz−1), which requires the presence of a giant black hole with a sufficient accretion rate, and also with a rapid rotation, which in turn can be provided by major merging.

Destroying a Kerr Black Hole

Based on three fundamentals aspects presented by Penrose, Wald, and Hawking, the black hole’s destroying scenario can be made. The main problem of this destroying process is about the presence of black hole’s angular momentum and charge. Especially for this research which is only taking an action into a rotating uncharged black hole (Kerr Black Hole). This research showed that in order to destroy a Kerr Black Hole (especially a near-extremal Kerr Black Hole) , one needs to remove its angular momentum instead by forcing it in extremal conditions and let Hawking Radiation occurs. On the other hand, the research showed that particle’s mass is linearly dependant in Penrose Process. The result also showed (which ; is a black hole’s angular momentum and is a black hole mass) cannot be reached because only black hole with negative net-energy can fulfil the condition. In another side, we calculated the minimum power needed by hole to kick the particles out. DOI: http://dx.doi.org/10.17977/um024v2i12017p007

Observing shadow of the Schwarzschild black hole in presence of a plasma

AbstractWe have investigated particle motion around Schwarzschild black holes in the presence of a plasma with radial power-law density profile has been shown that the photon sphere around a spherically symmetric black hole is unchanged under the influence of the plasma; however, the Schwarzschild black hole shadow size is reduced due to the refraction of electromagnetic radiation in the plasma environment of the black hole.