Eccentric Disk Research Articles

ALMA Observations of Proper Motions of the Dust Clumps in the Protoplanetary Disk MWC 758

To study the dust dynamics in the dust-trapping vortices in the protoplanetary disk around MWC 758, we analyzed the 1.3 mm continuum images of the MWC 758 disk obtained with the Atacama Large Millimeter/submillimeter Array in 2017 and 2021. We detect proper motions of 22 mas and 24 mas in the two dust clumps at radii of 0.″32 and 0.″54 in the disk on the plane of the sky, respectively. On the assumption that the dust clumps are located in the disk midplane, the velocities of the observed proper motions along the azimuthal direction of the inner and outer dust clumps are sub- and super-Keplerian, respectively, and both have angular velocities corresponding to the Keplerian angular velocity at a radius of 0.″46 ± 0.″04. This deviation from the Keplerian motion is not expected in the conventional theory of vortices formed by the Rossby wave instability. The observed non-Keplerian proper motions of the dust clumps are unlikely due to the disk warp and eccentricity, nor are they associated with any predicted planets. The two dust clumps are likely spatially coincident with the infrared spirals. In addition, we detect the changes in the intensity profiles of the dust clumps over the 4 yr span. Therefore, we suggest that the observed proper motions are possibly due to changes in the density distributions in the dust clumps caused by their interaction with the spirals in the disk.

Discs are born eccentric

Context. Recent observations have begun probing the early phases of disc formation, but little data yet exists on disc structure and morphology of Class 0 objects. Using simulations, we are able to lay out predictions of disc morphologies expected in future surveys of young discs. Based on detailed simulations of ab initio star formation by core collapse, we predict that early discs must be eccentric. Aims. In this Letter, we study the morphology and, in particular, the eccentricity of discs formed in non-ideal magnetohydrodynamic (MHD) collapse simulations. We attempt to show that discs formed by cloud collapse are likely to be eccentric. Methods. We ran non-ideal MHD collapse simulations in the adaptive mesh refinement code RAMSES with radiative transfer. We used state-of-the-art analysis methods to measure the disc eccentricity. Results. We find that despite no asymmetry in the initial conditions, the discs formed are eccentric, with eccentricities on the order of 0.1. Conclusions. These results may have important implications for protoplanetary disc dynamics and planet formation. The presence of eccentricity in young discs that is not seen at later stages of disc evolution is in tension with current viscous eccentricity damping models. This implies that there may be an as-yet undiscovered circularisation mechanism in circumstellar discs.

Constrained motion of self-propelling eccentric disks linked by a spring.

It has been supposed that the interplay of elasticity and activity plays a key role in triggering the non-equilibrium behaviors in biological systems. However, the experimental model system is missing to investigate the spatiotemporally dynamical phenomena. Here, a model system of an active chain, where active eccentric-disks are linked by a spring, is designed to study the interplay of activity, elasticity, and friction. Individual active chain exhibits longitudinal and transverse motions; however, it starts to self-rotate when pinning one end and self-beat when clamping one end. In addition, our eccentric-disk model can qualitatively reproduce such behaviors and explain the unusual self-rotation of the first disk around its geometric center. Furthermore, the structure and dynamics of long chains were studied via simulations without steric interactions. It was found that a hairpin conformation emerges in free motion, while in the constrained motions, the rotational and beating frequencies scale with the flexure number (the ratio of self-propelling force to bending rigidity), χ, as ∼(χ)4/3. Scaling analysis suggests that it results from the balance between activity and energy dissipation. Our findings show that topological constraints play a vital role in non-equilibrium synergy behaviors.

Counter-rotation and slow precession in aligned eccentric nuclear discs due to gravitational wave recoil kicks

ABSTRACT The M31 nucleus contains a supermassive black hole embedded in a massive stellar disc of apsidally aligned eccentric orbits. It has recently been shown that this disc is slowly precessing at a rate consistent with zero. Here, we demonstrate using N-body methods that apsidally aligned eccentric discs can form with a significant ($\sim$0.5) fraction of orbits counter-rotating as the result of a gravitational wave recoil kick of merging supermassive black holes. Higher amplitude kicks map to a larger retrograde fraction in the surrounding stellar population, which in turn results in slow precession. We furthermore show that discs with significant counter-rotation are more stable (i.e. apsidal alignment is most pronounced and long lasting), more eccentric, and have the highest rates of stars entering the black hole’s tidal disruption radius.

Orbital dynamics in the GG Tau A system: Investigating its enigmatic disc

Context. GG Tau is one of the most studied young multiple stellar systems: GG Tau A is a hierarchical triple surrounded by a massive disc and its companion, GG Tau B, is also a binary. Despite numerous observational attempts, a comprehensive understanding of the geometry of the GG Tau A system is still elusive. Given the significant role of dynamical interactions in shaping the evolution of these systems, it is relevant to characterise the stellar orbits and the discs’ properties. Aims. To determine the best orbital configuration of the GG Tau A system and its circumtriple disc, we provide new astrometric measures of the system and we run a set of hydrodynamical simulations with two representative orbits to test how they impact a disc composed of dust and gas. Methods. We tested the dynamical evolution of the two scenarios on short and long timescales. We obtained synthetic flux emission from our simulations at different timescales and we compared them with multi-wavelength observations of 1300 µm ALMA dust continuum emission and 1.67 µm SPHERE dust scattering to infer the most likely orbital arrangement. Results. We extend the analysis of the binary orbital parameters using six new epochs from archival data, showing that the current measurements alone (and future observations coming in the next 5–10 yr) are not capable of fully breaking the degeneracy between families of coplanar and misaligned orbits, but finding that a modest misalignment is probable. We find that the timescale for the onset of the disc eccentricity growth, τecc, is a fundamental timescale for the morphology of the system. Results from the numerical simulations obtained using the representative coplanar and misaligned (∆θ = 30°) orbits show that the best match between the position of the stars, the cavity size, and the dust ring size of GG Tau A is obtained with the misaligned configuration on timescales shorter than τecc. The results exhibit an almost circular cavity and dust ring, favouring slightly misaligned (∆θ ~ 10–30°) low-eccentricity (e ~ 0.2–0.4) orbits. However, for both scenarios, the cavity size and its eccentricity quickly grow for timescales longer than τecc and the models do not reproduce the observed morphology anymore. This implies that either the age of the system is shorter than τecc or that the disc eccentricity growth is not triggered or dissipated in the system. This finding raises questions about the future evolution of the GG Tau A system and, more generally, the time evolution of eccentric binaries and their circumbinary discs.

Planetesimal Drift in Eccentric Disks: Possible Outward Migration

Radial drift of solid particles in the protoplanetary disk is often invoked as a threat to planet formation, as it removes solid material from the disk before it can be assembled into planets. However, it may also concentrate solids at particular locations in the disk, thus accelerating the coagulation process. Planetesimals are thought to drift much faster in an eccentric disk, due to their higher velocities with respect to the gas, but their drift rate has only been calculated using approximate means. In this work, we show that in some cases previous estimates of the drift rate, based on a modification of the results for an axisymmetric disk, are highly inaccurate. In particular, we find that under some easily realized circumstances, planetesimals may drift outwards, rather than inwards. This results in the existence of radii in the disk that act as stable attractors of planetesimals. We show that this can lead to a local enhancement of more than an order of magnitude in the surface density of planetesimals, even when a wide dispersion of planetesimal size is considered.

Automatic compensation system for eccentricity error of absolute optical encoder.

Eccentric error is a vital part of high-precision optical encoder error. An automatic error compensation system is designed to lower the eccentric error of the encoder. On the periphery of the fan-shaped code path of the traditional encoder disk, a set of radial code paths is drawn. This radial code path is composed of several concentric circles with alternating light and dark lines. The direction of the radial code path is perpendicular to the direction of the fine code path. When the encoder rotates, the eccentricity of the encoder disk is measured by the moiré fringe signal output from the radial code channel. Based on the eccentricity error compensation algorithm, the eccentricity error of the encoder disk is compensated in real time to enhance the accuracy of the encoder. The experimental results of an encoder show that the mean square error of the encoder before the eccentricity error compensation is 21.25 arc seconds, and it is 3.66 arc seconds after compensation by this algorithm. The algorithm can significantly compensate the error caused by the eccentricity of the encoder and greatly improve the accuracy of the encoder.

Probing the eccentricity in protostellar discs: Modelling kinematics and morphologies

Context. Protostellar discs are mostly modelled as circular structures of gas and dust orbiting a protostar. However, a number of physical mechanisms, for example, the presence of a (sub)stellar companion or initial axial asymmetry, can cause the gas and dust orbital motion to become eccentric. Theoretical studies have revealed that, when present, disc eccentricity is expected to occur with predictable profiles that can be long-lasting and potentially observable in protostellar systems. Aims. We construct an analytical model predicting the typical features of the kinematics and morphology of eccentric protostellar discs, with the final goal of characterising the observational appearance of eccentricity in discs. Methods. We validate the model using a numerical simulation of a circumbinary disc (where the binary makes the disc eccentric). We finally post-process the simulation with Monte Carlo radiative transfer to study how eccentric features would appear through the ‘eyes’ of ALMA. Results. Besides the motion of the material on eccentric Keplerian orbits in the disc orbital plane, the most characteristic eccentric feature emerging from the analytical model is strong vertical motion with a typical anti-symmetric pattern (with respect to the disc line of pericentres). A circumbinary disc with a ≈ 40 au eccentric cavity (ecav = 0.2), carved by an abin = 15 au binary, placed at a distance d = 130 pc, is expected to host in its upper emission surface vertical oscillations up to vz ~ 400 m s−1 close to the cavity edge, that is to say, well within ALMA spectral and spatial resolution capabilities. A residual spiral pattern in the vertical velocity Δvz ~ 150 m s−1 of the simulation cannot be captured by the theoretical model, we speculate it to be possibly linked to the presence of a companion in the system.

Nonlinear vibrations and critical angular velocity information of the high-speed rotating eccentric disk made of Gori-metamaterials: Introducing data-driven solution for solving the nonlinear problems

Eccentric discs in rotational motion are commonly utilized in various technical fields, including gas turbine engines, flywheels, gears, and brakes. So, improving its critical angular velocity and frequency characteristics is a challenging issue for engineers. So, in this work for the first time, nonlinear vibrations and buckling analysis of the high-speed rotating eccentric disks using mathematical simulation and data-driven solutions are presented. One of the suggestions for improving its mechanical properties is considering metamaterials in the construction of the eccentric disk. Metamaterial is a novel synthetic material that has distinctive physical and mechanical capabilities that are unattainable in natural materials due to its well-designed structure. The properties of the eccentric disks are controlled by the amount of graphene and the degree of folding of graphene origami (GOri) across the thickness of the eccentric disks. These properties, such as Poisson's ratio, vary depending on the position and can be estimated using micromechanical models assisted by genetic programming (GP). Using von-Karman nonlinearity, transformed differential quadrature method (TDQM), and Newton's method the nonlinear governing equations are obtained and solved, respectively. The results show that when the radius ratio of the rotating eccentric disk increases by 8%, the critical point is decreased from 420 HZ to 370 HZ, a reduction of around 12 %. Another suggestion for improving its mechanical properties is controlling the geometrics and physics of the presented structure according to the designer's purposes.

The transient event in NGC 1566 from 2017 to 2019

Context. NGC 1566 is a local face-on Seyfert galaxy and is known for exhibiting recurrent outbursts that are accompanied by changes in spectral type. The most recent transient event occurred from 2017 to 2019 and was reported to be accompanied by a change in Seyfert classification from Seyfert 1.8 to Seyfert 1.2. Aims. We aim to study the transient event in detail by analyzing the variations in the optical broad-line profiles. In particular, we intend to determine the structure and kinematics of the broad-line region. Methods. We analyzed data from an optical spectroscopic variability campaign of NGC 1566 taken with the 9.2 m Southern African Large Telescope (SALT) between July 2018 and October 2019 triggered by the detection of hard X-ray emission in June 2018. We supplemented this data set with optical to near-infrared (NIR) spectroscopic archival data taken by VLT/MUSE in September 2015 and October 2017, and investigated the emission from different line species during the event. Results. NGC 1566 exhibits pronounced spectral changes during the transient event. We observe the emergence and fading of a strong power-law-like blue continuum as well as strong variations in the Balmer, He I, and He II lines and the coronal lines [Fe VII], [Fe X], and [Fe XI]. Moreover, we detect broad double-peaked emission line profiles of O Iλ8446 and the Ca IIλλ8498, 8542, 8662 triplet. This is the first time that genuine double-peaked O Iλ8446 and Ca IIλλ8498, 8542, 8662 emission in AGN is reported in the literature. All broad lines show a clear redward asymmetry with respect to their central wavelength and we find indications for a significant blueward drift of the total line profiles during the transient event. The profiles and the FWHM of the Balmer lines remain largely constant during all observations. We show that the double-peaked emission line profiles are well approximated by emission from a low-inclination, relativistic eccentric accretion disk, and that single-peaked profiles can be obtained by broadening due to scale-height-dependent turbulence. Small-scale features in the O I and Ca II lines suggest the presence of inhomogeneities in the broad-line region. Conclusions. We conclude that the broad-line region in NGC 1566 is dominated by the kinematics of a relativistic eccentric accretion disk. The broad-line region can be modeled to be vertically stratified with respect to scale-height turbulence with O I and Ca II being emitted close to the disk in a region with high (column) density, while the Balmer and helium lines are emitted at greater scale height above the disk. The observed blueward drift might be attributed to a low-optical-depth wind launched during the transient event. Except for this wind, the observed kinematics of the broad-line region remain largely unchanged during the transient event.

The Evolution of Accreting Binaries: From Brown Dwarfs to Supermassive Black Holes

Circumbinary accretion occurs throughout the universe, from the formation of stars and planets to the aftermath of major galactic mergers. We present an extensive investigation of circumbinary accretion disks, studying circular binaries with mass ratios (q ≡ M 2/M 1) from 0.01 to 1 and at each mass ratio probing the effects of disk thickness and viscosity. We study disks with aspect ratios H/r ∈ {0.1, 0.05, 0.03} and vary both the magnitude and spatial dependence of viscosity. Although thin accretion disks have previously been found to promote rapid inspirals of equal-mass binaries, we find that gravitational torques become weaker at lower mass ratios and most binaries with 0.01 ≤ q ≤ 0.04 outspiral, which may delay the coalescence of black hole binaries formed from minor mergers and cause high-mass exoplanets to migrate outward. However, in a number of cases, the disks accreting onto binaries with mass ratios ∼0.07 fail to develop eccentric modes, leading to extremely rapid inspirals. Variability in black hole accretion correlates with disk eccentricity, and we observe variability above the ∼10% level even for mass ratios of 0.01. We demonstrate that the spatial dependence of the viscosity (e.g., α vs. constant ν) significantly affects the degree of preferential accretion onto the secondary, resolving discrepancies between previous studies. Colder circumbinary disks remain eccentric even at q ∼ 0.01 and sustain deep, asymmetric cavities.

On the Rigidly Precessing, Eccentric Gas Disk Orbiting the White Dwarf SDSS J1228+1040

Metal pollution onto white dwarfs is a widespread phenomenon that remains puzzling. Some of these white dwarfs also harbor gaseous debris disks. Emission lines from these disks open a unique window to the physical properties of the polluting material, lending insights into their origin. We model the emission line kinematics for the gas disk around SDSS J1228+1040, a system that has been monitored for over two decades. We show that the disk mass is strongly peaked at 1 R ⊙ (modulo the unknown inclination), and the disk eccentricity decreases from a value of 0.44 at the inner edge, to nearly zero at the outer edge. This eccentricity profile is exactly what one expects if the disk is in a global eccentric mode, precessing rigidly under general relativity and gas pressure. The precession period is about two decades. We infer that the mass of the gas disk is roughly equivalent to that of a 50 km rocky body, while the mass of the accompanying dust disk is likely insignificant. The disk eccentricity confirms an origin in tidal disruption, while the short disk diffusion time suggests that the disruption event happened a few centuries ago. Moreover, we argue that the initial orbit for the disrupted body, and that of its putative planetary perturber, fall within an astronomical unit around the white dwarf. The total mass of the source population is likely orders of magnitude more massive than our own Asteroid belt and does not seem to exist around main-sequence stars.

Tidal Disruption of Planetesimals from an Eccentric Debris Disk Following a White Dwarf Natal Kick

The surfaces of many white dwarfs are polluted by metals, implying a recent accretion event. The tidal disruption of planetesimals is a viable source of white dwarf pollution and offers a unique window into the composition of exoplanet systems. The question of how planetary material enters the tidal disruption radius of the white dwarf is currently unresolved. Using a series of N-body simulations, we explore the response of the surrounding planetesimal debris disk as the white dwarf receives a natal kick caused by anisotropic mass loss on the asymptotic giant branch. We find that the kick can form an apse-aligned, eccentric debris disk in the range 30–240 au, which corresponds to the orbits of Neptune, the Kuiper Belt, and the scattered disk in our solar system. In addition, many planetesimals beyond 240 au flip to counterrotating orbits. Assuming an isotropic distribution of kicks, we predict that approximately 80% of white dwarf debris disks should exhibit significant apsidal alignment and a fraction of counterrotating orbits. The eccentric disk is able to efficiently and continuously torque planetesimals onto radial, star-grazing orbits. We show that the kick causes both an initial burst in tidal disruption events as well as an extended period of 100 Myr where tidal disruption rates are consistent with observed mass accretion rates on polluted white dwarfs.

Impact of Gestational Exposure to Individual and Combined Per- and Polyfluoroalkyl Substances on a Placental Structure and Efficiency: Findings from the Ma'anshan Birth Cohort.

Prenatal exposure to perfluoroalkyl and polyfluoroalkyl substances (PFASs) is inevitable among pregnant women. Nevertheless, there is a scarcity of research investigating the connections between prenatal PFAS exposure and the placental structure and efficiency. Based on 712 maternal-fetal dyads in the Ma'anshan Birth Cohort, we analyzed associations between individual and mixed PFAS exposure and placental measures. We repeatedly measured 12 PFAS in the maternal serum during pregnancy. Placental weight, scaling exponent, chorionic disc area, and disc eccentricity were used as the outcome variables. Upon adjusting for confounders and implementing corrections for multiple comparisons, we identified positive associations between branched perfluorohexane sulfonate (br-PFHxS) and 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) with placental weight. Additionally, a positive association was observed between br-PFHxS and the scaling exponent, where a higher scaling exponent signified reduced placental efficiency. Based on neonatal sex stratification, female infants were found to be more susceptible to the adverse effects of PFAS exposure. Mixed exposure modeling revealed that mixed PFAS exposure was positively associated with placental weight and scaling exponent, particularly during the second and third trimesters. Furthermore, br-PFHxS and 6:2 Cl-PFESA played major roles in the placental measures. This study provides the first epidemiological evidence of the relationship between prenatal PFAS exposure and placental measures.

Three-body encounters in black hole discs around a supermassive black hole

Context. Dynamical encounters of stellar-mass black holes (BHs) in a disc of compact objects around a supermassive BH (SMBH) can accelerate the formation and coalescence of BH binaries. It has been proposed that binary–single encounters among BHs in such discs can lead to an excess of highly eccentric BH mergers. However, previous studies have neglected how the disc velocity dispersion and the SMBH’s tidal field affect the three-body dynamics. Aims. We investigate the outcomes of binary–single encounters considering different values of the disc velocity dispersion, and examine the role of the SMBH’s tidal field. We then demonstrate how their inclusion affects the properties of merging BH binaries. Methods. We performed simulations of four-body encounters (i.e. with the SMBH as the fourth particle) using the highly accurate, regularised code TSUNAMI, which includes post-Newtonian corrections up to order 3.5PN. To isolate the effect of the SMBH’s tidal field, we compared these simulations with those of three-body encounters in isolation. Results. The disc velocity dispersion controls how orbits in the disc are aligned and circular, and determines the relative velocity of the binary–single pair before the encounter. As the velocity dispersion decreases, the eccentricity of post-encounter binaries transitions from thermal to superthermal, and binaries experience enhanced hardening. The transition between these two regimes happens at disc eccentricities and inclinations of order e ∼ i ∼ 10−4. These distinct regimes correspond to a disc dominated by random motions (e ∼ i ≳ 10−4) and one dominated by the Keplerian shear (e ∼ i ≲ 10−4). The effect of the SMBH’s tidal field depends on the velocity dispersion of the disc. When the velocity dispersion is low, the resulting binaries are less eccentric compared to isolated encounters. Conversely, binaries become less eccentric compared to isolated encounters at high velocity dispersion. This also affects the number of BH mergers. Conclusions. The inclusion of the SMBH’s tidal field and the disc velocity dispersion can significantly affect the number of GW mergers, and especially the number of highly eccentric inspirals. These can be up to ∼2 times higher at low velocity dispersion, and ∼12 times lower at high velocity dispersions. The spin–orbit alignment is influenced by the tidal field exclusively at high velocity dispersions, effectively inhibiting the formation of anti-aligned binary BHs. Nonetheless, encounters in random-motion-dominated discs around a SMBH are still more effective in producing GW mergers compared to those occurring in spherically symmetric nuclear star clusters without an SMBH.

Nonlinear model updating of the rotor-bearing system by multi-harmonic balance method and analytical sensitivity derivation

Responses of the bearing system are usually predicted or tested, to analyze its nonlinear dynamic characteristics. However, responses predicted from the bearing model constructed by Hertz contact theory usually show differences with their tested counterparts, denoting the improper setting of the nonlinear contact parameters. It is compulsory to reduce such differences and obtain a precise bearing model using nonlinear model updating techniques. In this paper, a novel nonlinear model updating framework is proposed following the Multi-Harmonic Balance Method (MHBM) and the analytical sensitivity analysis, for updating of the rotor-bearing system using the nonlinear responses in the frequency domain. With the derivation of bearing response sensitivities to the nonlinear contact parameters, increments of the nonlinear parameters can be ascertained by the sensitivity inverse and updating of the nonlinear bearing model can be implemented in an iterative way, until a precise bearing model with the response differences reduced to minima is obtained. Firstly, a novel MHBM model is derived for the bearing system, which is fully described by matrix operations and used to further deduce the analytical sensitivity formulations of the bearing responses to the design parameters. Afterwards, the bearing responses and sensitivities in the frequency domain are predicted by the continuation strategy. Finally, model updating is conducted for the bearing system using the traditional inverse-sensitivity framework. Two cases are used to demonstrate the feasibility of the method. The first case is to update bearing parameters of contact stiffness, clearance and eccentricity of a 2-DOF bearing system in order to match the predicted bearing responses with the measured ones in strong nonlinearity with the multivalued phenomenon. The next is to update the Hertz contact parameters of the left and right bearings, together with the disc eccentricity, of a Finite Element (FE) rotor-bearing system. These results show the validity and superiority of the proposed method.

Analysis of Dynamic Characteristics of Rotor Sail Using a 4DOF Rotor Model and Finite Element Model

The interest in wind-assisted ship propulsions (WASPs) is increasing to improve fuel efficiency and to reduce greenhouse gas emissions in ships. A rotor sail, one of the typical WASPs, can provide auxiliary propulsive force by rotating a cylinder-shaped structure based on the Magnus effect. However, due to its huge rotating structure, a meticulous evaluation of the influence on the ship structure and dynamical stability of the rotating structure should be conducted in the design stage. In this respect, an analysis of the rotating structure for a 30 m height and 3 m diameter rotor sail was conducted in this study. First, a 4DOF (four-degree-of-freedom) model was derived to simplify the dynamics of the rotor sail. Using the 4DOF model, natural frequencies for four low-order modes of the rotor sail were calculated, and frequency responses at support points were predicted. Next, a comparison and validation with the finite element model of the rotor sail were carried out. For the 1st and 2nd natural frequencies, a difference of approximately 0.3 Hz was observed between the 4DOF model and the finite element model, confirming the effectiveness of the 4DOF model for low-order modes. In analysis with changes in the bearing supporting stiffnesses, it was verified that lower support bearings have a significant impact on rotor dynamics compared to upper support bearings. Vibration response at the upper support was also confirmed through frequency response analysis caused by imbalance at Thom disk and mid-plate. Additionally, when estimating the eccentricity of the Thom disk as imbalance, a limit of eccentricity error could be set as 24 mm. The presented modeling procedures and analysis results can be references during early design stage of a novel rotor sail structure.

A uniform analysis of debris discs with the Gemini Planet Imager II: constraints on dust density distribution using empirically informed scattering phase functions

ABSTRACT Spatially resolved images of debris discs are necessary to determine disc morphological properties and the scattering phase function (SPF) thatantifies the brightness of scattered light as a function of phase angle. Current high-contrast imaging instruments have successfully resolved several dozens of debris discs around other stars, but few studies have investigated trends in the scattered-light, resolved population of debris discs in a uniform and consistent manner. We have combined Karhunen-Loeve Image Projection (KLIP) with radiative-transfer disc forward modelling in order to obtain the highest-quality image reductions and constrain disc morphological properties of eight debris discs imaged by the Gemini Planet Imager at H-band with a consistent and uniformly applied approach. In describing the scattering properties of our models, we assume a common SPF informed from solar system dust scattering measurements and apply it to all systems. We identify a diverse range of dust density properties among the sample, including critical radius, radial width, and vertical width. We also identify radially narrow and vertically extended discs that may have resulted from substellar companion perturbations, along with a tentative positive trend in disc eccentricity with relative disc width. We also find that using a common SPF can achieve reasonable model fits for discs that are axisymmetric and asymmetric when fitting models to each side of the disc independently, suggesting that scattering behaviour from debris discs may be similar to Solar system dust.

Evolution of eccentric stellar discs around supermassive black holes: the complex disc disruption dynamics and the milliparsec stars

ABSTRACT We study the 10 Myr evolution of parsec-scale stellar discs with initial masses of Mdisc = 1.0–$7.5 \times 10^4\, \mathrm{M}_\odot$ and eccentricities einit = 0.1–0.9 around supermassive black holes (SMBHs). Our disc models are embedded in a spherical background potential and have top-heavy single and binary star initial mass functions (IMF) with slopes of 0.25–1.7. The systems are evolved with the N-body code BIFROST, including post-Newtonian (PN) equations of motion and simplified stellar evolution. All discs are unstable and evolve on Myr time-scales towards similar eccentricity distributions peaking at e⋆ ∼ 0.3–0.4. Models with high einit also develop a very eccentric (e⋆ ≳ 0.9) stellar population. For higher disc masses Mdisc ≳ 3 × 104 M⊙, the disc disruption dynamics is more complex than the standard secular eccentric disc instability with opposite precession directions at different disc radii – a precession direction instability. We present an analytical model describing this behaviour. A milliparsec population of N ∼ 10–100 stars forms around the SMBH in all models. For low einit, stars migrate inward while for einit ≳ 0.6 stars are captured by the Hills mechanism. Without PN, after 6 Myr, the captured stars have a sub-thermal eccentricity distribution. We show that including PN effects prevents this thermalization by suppressing resonant relaxation effects and cannot be ignored. The number of tidally disrupted stars is similar or larger than the number of milliparsec stars. None of the simulated models can simultaneously reproduce the kinematic and stellar population properties of the Milky Way centre clockwise disc and the S-cluster.

Anisotropic Star Clusters around Recoiling Supermassive Black Holes

Gravitational-wave recoil kicks from merging supermassive black hole binaries can have a profound effect on the surrounding stellar population. In this work, we study the dynamic and kinematic properties of nuclear star clusters following a recoil kick. We show that these postkick structures present unique signatures that can provide key insight to observational searches for recoiling supermassive black holes. In our previous paper, we showed that an in-plane recoil kick turns a circular disk into a lopsided, eccentric disk such as the one we observe in the Andromeda nucleus. Building on this work, here we explore many recoil kick angles as well as initial stellar configurations. For a circular disk of stars, an in-plane kick causes strong apsidal alignment with a significant fraction of the disk becoming retrograde at large radii. If the initial orbits are highly eccentric, an in-plane kick forms a bar-like structure made up of two antialigned lopsided disks. An out-of-plane kick causes clustering in the argument of periapsis, ω, regardless of the initial eccentricity distribution. Initially, isotropic configurations form anisotropies in the form of a torus of eccentric orbits oriented perpendicular to the recoil kick. Postkick surface density and velocity maps are presented in each case to highlight the distinct, observable structures of these systems.