Hole Orbits Research Articles

Dual effect of string cloud and dark matter halos on particle motions, shadows and epicyclic oscillations around Schwarzschild black holes

In this work, we study the particle dynamics, shadows and quasi-periodic oscillations around the Schwarzschild black hole with three different dark matter halos and string cloud parameters. The motion of particles is considered with the string cloud parameter α and investigated for massive and massless particles. The photon orbits and inner stable circular orbits of these black holes are obtained from the effective potential. The black hole shadows are calculated using three different dark matter halos. The shadow radius of these black holes increases compared to a pure Schwarzschild black hole for different values of the string cloud parameter. Further, quasi-periodic oscillations are also discussed in the current analysis. Our study examines how the radial profiles of orbital and radial harmonic oscillation frequencies change with the string cloud parameter. This study examines the major properties of test particle's quasi-periodic oscillations near stable circular orbits in the black hole equatorial plane. Our findings indicate that observational tests for black holes influenced by dark matter halos and cloud strings are also feasible and viable.

Constraining the nuclear equation of state from orbits of primordial black holes inside neutron stars

Constraining the nuclear equation of state from orbits of primordial black holes inside neutron stars

A calibrated model for N-body dynamical friction acting on supermassive black holes

Abstract Black holes are believed to be crucial in regulating star formation in massive galaxies, which makes it essential to faithfully represent the physics of these objects in cosmological hydrodynamics simulations. Limited spatial and mass resolution and the associated discreteness noise make following the dynamics of black holes especially challenging. In particular, dynamical friction, which is responsible for driving massive black holes towards the centres of galaxies, cannot be accurately modelled with softened N-body interactions. A number of subgrid models have been proposed to mimic dynamical friction or directly include its full effects in simulations. Each of these methods has its individual benefits and shortcomings, while all suffer from a common issue of being unable to represent black holes with masses below a few times the simulated dark matter particle mass. In this paper, we propose a correction for unresolved dynamical friction, which has been calibrated on simulations run with the code KETJU, in which gravitational interactions of black holes are not softened. We demonstrate that our correction is able to sink black holes with masses greater than the dark matter particle mass at the correct rate. We show that the impact of stochasticity is significant for low-mass black holes (MBH ≤ 5MDM) and propose a correction for stochastic heating. Combined, this approach is applicable to next generation cosmological hydrodynamics simulations that jointly track galaxy and black hole growth with realistic black hole orbits.

Forming off-center massive black hole binaries in dwarf galaxies through Jacobi capture

It is well established that black holes reside in the central regions of virtually all types of known galaxies. Recent observational and numerical studies however challenge this picture, suggesting that intermediate-mass black holes in dwarf galaxies may be found on orbits far from the center. In particular, constant-density cores minimize orbital energy losses due to dynamical friction, and allow black holes to settle on stable off-center orbits. Using controlled simulations, we study the dynamics of off-center black holes in dwarf galaxies with such cores. We propose a new scenario to describe off-center mergers of massive black holes, starting with a Jacobi capture. We focus on initially circular and co-planar black hole orbits and explore a large parameter space of black hole masses and orbital parameters. We find that Jacobi captures are a complex and chaotic phenomenon that occurs in about 13% of cases in this simplified setup, and we quantify how the likelihood of capture depends on the simulation parameters. We note that this percentage is likely an upper limit of the general case. Nevertheless, we show that Jacobi captures in cored dwarf galaxies can facilitate the formation of off-center black hole binaries, and that this process is sufficiently common to have a substantial effect on black hole growth. While our setup only allows for temporary captures, we expect dissipative forces from baryons and post-Newtonian corrections to maintain the captures over time and to lead to the formation of stable binary systems. This motivates future studies of the effectiveness of such dissipative forces, within stripped nuclei or globular clusters, in forming stable bound systems.

Probing the tunable multi-cone band structure in Bernal bilayer graphene

Bernal bilayer graphene (BLG) offers a highly flexible platform for tuning the band structure, featuring two distinct regimes. One is a tunable band gap induced by large displacement fields. Another is a gapless metallic band occurring at low fields, featuring rich fine structure consisting of four linearly dispersing Dirac cones and van Hove singularities. Even though BLG has been extensively studied experimentally, the evidence of this band structure is still elusive, likely due to insufficient energy resolution. Here, we use Landau levels as markers of the energy dispersion and analyze the Landau level spectrum in a regime where the cyclotron orbits of electrons or holes in momentum space are small enough to resolve the distinct mini Dirac cones. We identify the presence of four Dirac cones and map out topological transitions induced by displacement field. By clarifying the low-energy properties of BLG bands, these findings provide a valuable addition to the toolkit for graphene electronics.

Synthesis, formation mechanism, and intrinsic physical properties of several As/P-containing MAX phases

• Molten-salt sintering is applicable to P-based MAX phases • Solid-state sintering is suitable to As-based MAX phases • Route 1: NbP+Nb+C → Nb 3 P 2 C is most favorable to obtain pure Nb 3 P 2 C • Molten-salt sintering do well on all routes, especially for Nb 2 PC+NbP→Nb 3 P 2 C • Various intrinsic physical properties of 321 phases are firstly reported 321 phases are an atypical series of MAX phases, in which A = As/P, with superior elastic properties, featuring in the MA-triangular-prism bilayers in the crystal structure. Until now, besides Nb 3 As 2 C, the pure phases of the other 321 compounds have not been realized, hampering the study of their intrinsic properties. Here, molten-salt sintering (MSS) and solid-state synthesis (SSS) were applied to synthesize As/P-containing 321 phases and 211 phases. Analyzing the phase composition of the end-product via multiple-phase Rietveld refinement, we found that MSS can effectively improve the purity of P-containing MAX phases, with the phase content up to 99% in Nb 3 P 2 C and 75.4(5)% in Nb 2 PC. In contrast, MSS performed poorly on As-containing MAX phases, only 8.9(4)% for Nb 3 As 2 C and 64(2)% for Nb 2 AsC, as opposed to the pure phases obtained by SSS. The experimental analyses combined with first-principles calculations reveal that the dominant formation route of Nb 3 P 2 C is through NbP + Nb + C → Nb 3 P 2 C. Moreover, we found that the benefits of MSS on P-containing MAX phases are on the facilitation of three considered chemical reaction routes, especially on Nb 2 PC + NbP → Nb 3 P 2 C. Furthermore, the intrinsic physical properties and Fermi surface topology of two 321 phases consisting of electron, hole, and open orbits are revealed theoretically and experimentally, in which the electron carriers are dominant in electrical transport. The feasible synthesis methods and the formation mechanism are instructive to obtain high-purity As/P-containing MAX phases and explore new MAX phases. Meanwhile, the intrinsic physical properties will give great support for future applications on 321 phases.

Precisely computing bound orbits of spinning bodies around black holes. I. General framework and results for nearly equatorial orbits

Very large mass ratio binary black hole systems are of interest both as a clean limit of the two-body problem in general relativity, as well as for their importance as sources of low-frequency gravitational waves. At lowest order, the smaller body moves along a geodesic of the larger black hole's spacetime. Accurate models of such systems require postgeodesic corrections to this motion. Postgeodesic effects that drive the small body away from the geodesic include the gravitational self-force, which incorporates the backreaction of gravitational-wave emission, and the spin-curvature force, which arises from coupling of the small body's spin to the black hole's spacetime curvature. In this paper, we describe a method for precisely computing bound orbits of spinning bodies about black holes. Our analysis builds off of pioneering work by Witzany which demonstrated how to describe the motion of a spinning body to linear order in the small body's spin. Exploiting the fact that in the large mass-ratio limit spinning-body orbits are close to geodesics (in a sense that can be made precise) and using closed-form results due to van de Meent describing precession of the small body's spin along black hole orbits, we develop a frequency-domain formulation of the motion which can be solved very precisely. We examine a range of orbits with this formulation, focusing in this paper on orbits which are eccentric and nearly equatorial (i.e., the orbit's motion is $\mathcal{O}(S)$ out of the equatorial plane), but for which the small body's spin is arbitrarily oriented. We discuss generic orbits with general small-body spin orientation in a companion paper. We characterize the behavior of these orbits, contrasting them with geodesics, and show how the small body's spin shifts the frequencies ${\mathrm{\ensuremath{\Omega}}}_{r}$ and ${\mathrm{\ensuremath{\Omega}}}_{\ensuremath{\phi}}$ which affect orbital motion. These frequency shifts change accumulated phases which are direct gravitational-wave observables, illustrating the importance of precisely characterizing these quantities for gravitational-wave observations.

Eccentricity evolution of compact binaries and applications to gravitational-wave physics

Searches for gravitational waves from compact binaries focus mostly on quasi-circular motion, with the rationale that wave emission circularizes the orbit. Here, we study the generality of this result, when astrophysical environments (e.g., accretion disks) or other fundamental interactions are taken into account. We are motivated by possible electromagnetic counterparts to binary black hole coalescences and orbits, but also by the possible use of eccentricity as a smoking-gun for new physics. We find that: i) backreaction from radiative mechanisms, including scalars, vectors and gravitational waves circularize the orbital motion. ii) by contrast, environmental effects such as accretion and dynamical friction increase the eccentricity of binaries. Thus, it is the competition between radiative mechanisms and environmental effects that dictates the eccentricity evolution. We study this competition within an adiabatic approach, including gravitational radiation and dynamical friction forces. We show that that there is a critical semi-major axis below which gravitational radiation dominates the motion and the eccentricity of the system decreases. However, the eccentricity inherited from the environment-dominated stage can be substantial, and in particular can affect LISA sources. We provide examples for GW190521-like sources.

Comparison of stellar populations in simulated and real post-starburst galaxies in MaNGA

ABSTRACT Recent integral field spectroscopic (IFS) surveys have revealed radial gradients in the optical spectral indices of post-starburst (PSB) galaxies, which can be used to constrain their formation histories. We study the spectral indices of post-processed mock IFS datacubes of binary merger simulations, carefully matched to the properties of the MaNGA IFS survey, with a variety of black hole (BH) feedback models, progenitor galaxies, orbits, and mass ratios. Based on our simulation sample, we find that only major mergers on prograde–prograde or retrograde–prograde orbits in combination with a mechanical BH feedback model can form galaxies with weak enough ongoing star formation, and therefore absent H α emission, to be selected by traditional PSB selection methods. We find strong fluctuations in nebular emission line strengths, even within the PSB phase, suggesting that H α selected PSBs are only a subsample of the underlying population. The global PSB population can be more robustly identified using stellar continuum-based approaches. The difficulty in reproducing the very young PSBs in simulations potentially indicates that new sub-resolution star formation recipes are required to properly model the process of star formation quenching. In our simulations, we find that the starburst peaks at the same time at all radii, but is stronger and more prolonged in the inner regions. This results in a strong time evolution in the radial gradients of the spectral indices that can be used to estimate the age of the starburst without reliance on detailed star formation histories from spectral synthesis models.

The Closest Black Hole Is 1,000 Light-Years Away

An unseen object—probably a black hole—orbits with two normal stars in our cosmic neighborhood.

Bound orbits of a slowly evolving black hole

Bound orbits of black holes are very well understood. Given a Kerr black hole of mass $M$ and spin $S = aM^2$, it is simple to characterize its orbits as functions of the orbit's geometry. How do the orbits change if the black hole is itself evolving? How do the orbits change if the orbiting body evolves? In this paper, we consider a process that changes a black hole's mass and spin, acting such that the spacetime is described by the Kerr solution at any moment, or that changes the orbiting body's mass. Provided this change happens slowly, the orbit's actions ($J_r, J_\theta, J_\phi$) are {\it adiabatic invariants}, and thus are constant during this process. By enforcing adiabatic invariance of the actions, we deduce how an orbit evolves due to changes in the black hole's mass and spin and in the orbiting body's mass. We demonstrate the impact of these results with several examples: how an orbit responds if accretion changes a black hole's mass and spin; how it responds if the orbiting body's mass changes due to accretion; and how the inspiral of a small body into a black hole is affected by change to the hole's mass and spin due to the gravitational radiation absorbed by the event horizon. In all cases, the effect is very small, but can be an order of magnitude or more larger than what was found in previous work which did not take into account how the orbit responds due to these effects.

Population Estimates for Electromagnetically Distinguishable Supermassive Binary Black Holes

Abstract Distinguishing the photon output of an accreting supermassive black hole binary system from that of a single supermassive black hole accreting at the same rate is intrinsically difficult because the majority of the light emerges from near the innermost stable orbits of the black holes. However, there are two possible signals that can distinctively mark binaries, both arising from the gap formed in circumbinary accretion flows inside approximately twice the binary separation. One of these is a “notch” cut into the thermal spectra of these systems in the IR/optical/UV, the other a periodically varying excess hard X-ray luminosity whose period is of order the binary orbital period. Using data from detailed galaxy evolution simulations, we estimate the distribution function in mass, mass ratio, and accretion rate for accreting supermassive binary black holes (SMBBHs) as a function of redshift and then transform this distribution function into predicted source counts for these two potential signals. At flux levels ≳10−13 erg cm−2 s−1, there may be ∼O(102) such systems in the sky, mostly in the redshift range 0.5 ≲ z ≲ 1. Roughly 10% should have periods short enough (≲5 yr) to detect the X-ray modulation; this is also the period range accessible to Pulsar Timing Array observations.

Constraining Quasar Relativistic Reflection Regions and Spins with Microlensing

Abstract We present an analysis of Chandra spectra of five gravitationally lensed active galactic nuclei. We confirm the previous detections of FeKα emission lines in most images of these objects with high significance. The line energies range from 5.8 to 6.8 keV, with widths from unresolved to 0.6 keV, consistent with emission close to spinning black holes viewed at different inclination angles. We also confirm the positive offset from the Iwasawa–Taniguchi effect, the inverse correlation between the FeKα equivalent width (EW) and the X-ray luminosity in active galactic nuclei, where our measured EWs are larger in lensed quasars. We attribute this effect to microlensing, and perform a microlensing likelihood analysis to constrain the emission size of the relativistic reflection region and the spin of supermassive black holes, assuming that the X-ray corona and the reflection region, responsible for the iron emission line, both follow power-law emissivity profiles. The microlensing analysis yields strong constraints on the spin and emissivity index of the reflection component for Q 2237+0305, with a > 0.92 and n > 5.4. For the remaining four targets, we jointly constrain the two parameters, yielding a = 0.8 ± 0.16 and an emissivity index of n = 4.0 ± 0.8, suggesting that the relativistic X-ray reflection region is ultracompact and very close to the innermost stable circular orbits of black holes, which are spinning at close to the maximal value. We successfully constrain the half-light radius of the emission region to <2.4 r g (r g = GM/c 2) for Q 2237+0305 and in the range 5.9–7.4 r g for the joint sample.

A new hybrid technique for modeling dense star clusters

The “gravitational million-body problem,” to model the dynamical evolution of a self-gravitating, collisional N-body system with ∼106 particles over many relaxation times, remains a major challenge in computational astrophysics. Unfortunately, current techniques to model such systems suffer from severe limitations. A direct N-body simulation with more than 105 particles can require months or even years to complete, while an orbit-sampling Monte Carlo approach cannot adequately model the dynamics in a dense cluster core, particularly in the presence of many black holes. We have developed a new technique combining the precision of a direct N-body integration with the speed of a Monte Carlo approach. Our Rapid And Precisely Integrated Dynamics code, the RAPID code, statistically models interactions between neighboring stars and stellar binaries while integrating directly the orbits of stars or black holes in the cluster core. This allows us to accurately simulate the dynamics of the black holes in a realistic globular cluster environment without the burdensome N^{2} scaling of a full N-body integration. We compare RAPID models of idealized globular clusters to identical models from the direct N-body and Monte Carlo methods. Our tests show that RAPID can reproduce the half-mass radii, core radii, black hole ejection rates, and binary properties of the direct N-body models far more accurately than a standard Monte Carlo integration while remaining significantly faster than a full N-body integration. With this technique, it will be possible to create more realistic models of Milky Way globular clusters with sufficient rapidity to explore the full parameter space of dense stellar clusters.

An axion-like scalar field environment effect on binary black hole merger

The environment, such as an accretion disk, could modify the signal of the gravitational wave from astrophysical black hole binaries. In this article, we model the matter field around intermediate-mass binary black holes by means of an axion-like scalar field and investigate their joint evolution. In detail, we consider equal mass binary black holes surrounded by a shell of axion-like scalar field both in spherically symmetric and non-spherically symmetric cases, and with different strengths of the scalar field. Our result shows that the environmental scalar field could essentially modify the dynamics. Firstly, in the spherically symmetric case, with increase of the scalar field strength, the number of circular orbits for the binary black hole is reduced. This means that the scalar field could significantly accelerate the merger process. Secondly, once the scalar field strength exceeds a certain critical value, the scalar field could collapse into a third black hole with its mass being larger than that of the binary. Consequently, the new black hole that collapses from the environmental scalar field could accrete the binary promptly and the binary collides head-on with each other. In this process, there is almost no quadrupole signal produced, and, consequently, the gravitational wave is greatly suppressed. Thirdly, when the scalar field strength is relatively smaller than the critical value, the black hole orbit could develop eccentricity through accretion of the scalar field. Fourthly, during the initial stage of the inspiral, the gravitational attractive force from the axion-like scalar field could induce a sudden turn in the binary orbits, hence resulting in a transient wiggle in the gravitational waveform. Finally, in the non-spherical case, the scalar field could gravitationally attract the binary moving toward the center of mass for the scalar field and slow down the merger process.

Energetic constraints on electromagnetic signals from double black hole mergers

Abstract The possible Fermi detection of an electromagnetic counterpart to the double black hole merger GW150914 has inspired many theoretical models, some of which propose that the holes spiralled together inside a massive star. However, we show that the heat produced by the dynamical friction on such black hole orbits can exceed the stellar binding energy by a large factor, which means that this heat could destroy the star. The energy scale of the explosion and the terminal velocity of the gas can be much larger than those in conventional supernovae. If the star unbinds before the merger, it would be hard for enough gas to remain near the holes at the merger to produce a gamma-ray burst, and this consideration should be taken into account when models are proposed for electromagnetic counterparts to the coalescence of two stellar-mass black holes. We find that only when the two black holes form very close to the centre can the star certainly avoid destruction. In that case, dynamical friction can make the black holes coalesce faster than they would in vacuum, which leads to a modification of the gravitational waveform that is potentially observable by advanced LIGO.

Lux in obscuro: photon orbits of extremal black holes revisited

It has been shown in the literature that the event horizon of an asymptotically flat extremal Reissner–Nordström black hole is also a stable photon sphere. We further clarify this statement and give a general proof that this holds for a large class of static spherically symmetric black hole spacetimes with an extremal horizon. In contrast, in the Doran frame, an asymptotically flat extremal Kerr black hole has an unstable photon orbit on the equatorial plane of its horizon. In addition, we show that an asymptotically flat extremal Kerr–Newman black hole exhibits two equatorial photon orbits if , one of which is on the extremal horizon in the Doran frame and is stable, whereas the second one outside the horizon is unstable. For , there is only one equatorial photon orbit, located on the extremal horizon, and it is unstable. There can be no photon orbit on the horizon of a non-extremal Kerr–Newman black hole.

Strong-field tidal distortions of rotating black holes. II. Horizon dynamics from eccentric and inclined orbits

In a previous paper, we developed tools for studying the horizon geometry of a Kerr black hole that is tidally distorted by a binary companion using techniques that require large mass ratios but can be applied to any bound orbit and allow for arbitrary black hole spin. We now apply these tools to generic Kerr black hole orbits. This allows us to investigate horizon dynamics: the tidal field perturbing the horizon's geometry varies over a generic orbit, with significant variations for eccentric orbits. Many of the features of the horizon's behavior found previously carry over to the dynamical case in a natural way. In particular, we find significant offsets between the applied tide and the horizon's response. This leads to bulging in the horizon's geometry which can lag or lead the orbit, depending upon the hole's rotation and the orbit's geometry. An interesting and apparently new feature we find are small-amplitude, high-frequency oscillations in the horizon's response. We have not been able to identify a mechanism for producing these oscillations, but find that they appear most clearly when rapidly rotating black holes are distorted by very strong-field orbits.

Neurosurgical Management of Nonmissile Penetrating Cranial Lesions

The objective of this study is to present a case series of nonmissile penetrating (NMP) injuries and to establish a workflow for an uncommon mechanism of traumatic head injury through the analysis of each case, classification of the type of lesion, management, and outcome score at follow-up. From January 1991 to December 2008, 36,000 patients presenting with traumatic brain injury (TBI) were admitted in the Department of Neurosurgery, Hospital Antônio Targino, Campina Grande-PB, Brazil. From these patients, 11 presenting with lesions caused by NMP objects were selected. Among the 11 patients, 9 were men and 2 were women. Their ages ranged from 7 to 74 years old (mean age ± SD, 29.1 ± 22.99 years). All patients underwent neuroradiologic evaluation. The entry point was classified as natural (orbit) or artificial (skull transfixation), and we also divided the patients presenting with secondary parenchymal or vascular damage from those presenting with only lesions caused by the primary penetration into the cranium and meninges. All patients were neurosurgically treated with removal of the foreign body through craniotomy, except the patient whose object (pen) was removed without craniotomy with local anesthesia. Glasgow Coma Scale (GCS) score on admission was a statistically significant factor on prognosis, and any patient who presented with a GCS score of 15 evolved satisfactorily, and there were no deaths in this group of patients (P= 0.04). TBIs caused by NMP objects are unusual and caused by aggression, self-inflicted harm (in the case of psychiatric patients), and accident. The foreign body may enter into the skull through a natural hole (orbit, nose, mouth, or ear) or crosses the skull, causing a fracture and creating an artificial hole. Preoperative neuroradiologic assessment is paramount for the correct neurosurgical approach. The main prognostic factor for these patients is the GCS score at admission.

Real weights, bound states and duality orbits

We show that the duality orbits of extremal black holes in supergravity theories with symmetric scalar manifolds can be derived by studying the stabilizing subalgebras of suitable representatives, realized as bound states of specific weight vectors of the corresponding representation of the duality symmetry group. The weight vectors always correspond to weights that are real, where the reality properties are derived from the Tits–Satake diagram that identifies the real form of the Lie algebra of the duality symmetry group. Both [Formula: see text] magic Maxwell–Einstein supergravities and the semisimple infinite sequences of [Formula: see text] and [Formula: see text] theories in [Formula: see text] and [Formula: see text] are considered, and various results, obtained over the years in the literature using different methods, are retrieved. In particular, we show that the stratification of the orbits of these theories occurs because of very specific properties of the representations: in the case of the theory based on the real numbers, whose symmetry group is maximally noncompact and therefore all the weights are real, the stratification is due to the presence of weights of different lengths, while in the other cases it is due to the presence of complex weights.