Mass Accretion Research Articles

Oscillating wind accretion due to X-ray inhibition of line-driven mechanism

Abstract In a high-mass X-ray binary system with a massive donor, the line-driven stellar wind accretes on to a compact object, emitting X-rays in the process. Ionizing the stellar wind matter using X-rays inhibits its acceleration, leading to changes in wind velocity due to X-ray irradiation from the compact accretor. Since the stellar wind velocity influences mass accretion rate and subsequent X-ray luminosity, the inhibiting effect of X-ray ionization on wind acceleration could potentially impact the mass accretion process. This study investigates the correlation between the accretion rate on a compact object and the acceleration process of stellar wind matter by using a simple model. Results indicate that the mass accretion rate exhibits spontaneous oscillations, causing quasiperiodic flares when considering the ionization of wind matter. Such a feedback process of X-ray ionization on the mass accretion rate could be related to the mechanism of flare production in X-ray binaries.

Jets are the most robust observable ingredient of common envelope evolution

Abstract I examine images of 50 planetary nebulae (PNe) with observable post-common envelope evolution (CEE) binary central stars and find that jets are about 40 percent more common than dense equatorial outflows. Because, in some cases, energetic jets can compress an equatorial outflow and because fast jets might disperse early in the PN evolution and avoid detection, the CEE process is likelier to launch jets than to eject a dense equatorial outflow by a larger factor than 1.4. In most cases, the companion, mainly a main sequence star, launches the jets as it accretes mass from the envelope of the giant star. By CEE jets, I also refer to jets launched shortly before the onset of the CEE, likely a grazing envelope evolution phase, and shortly after the CEE. The jets and the accretion of mass by the companion before, during, and after the CEE affect envelope mass removal and the final orbital separation. Most numerical simulations of the CEE ignore jets, and those that include jets omit other processes. Despite the considerable progress in the last decade with tens of hydrodynamical simulations of the CEE, we are still far from correctly simulating the CEE. Including jets in simulations of the CEE requires heavy computer resources, but it must be the next step.

Resolving the mass transfer in the symbiotic recurrent nova T Coronae Borealis

Context. T Coronæ Borealis (T CrB) is a symbiotic recurrent nova with an 80-year recurrence interval whose next eruption is imminent. Aims. We aim to resolve the accretion mechanism of the binary system governing the mass transfer during its super-active phase. Methods. Using phase-resolved high-resolution spectroscopy, we analyzed the zoo of spectral-line profiles arising from the symbiotic activity. We performed Doppler tomography of selected emission lines to resolve the system’s gaseous components and their different velocity regimes. Results. We find evidence of enhanced accretion through Roche lobe overflow during the super-active phase, as traced by the oxygen, helium, and hydrogen lines. The accretion disk is found to be fully viscously evolved and extends up to its maximal radius. By mapping the kinematics of lines probing different excitation energies, we can identify distinct interaction sites. These include the bright spot at the stream impact on the accretion disk outer radius, the irradiation at the red-giant facing side, the stream-disk overflow, the accretion disk wind, and an expanding nebula. The nebula emerged at the rise of the super-active phase and underwent an acceleration phase of about five years. The temporal evolution of the lines supports the scenario where the departure from quiescence started in the disk, likely triggered by a disk instability similar to what occurs in dwarf novae outburst, leading to an increased mass accretion and causing important irradiation of the giant that has further enhanced the mass-transfer rate during the super-active phase. Conclusions. Symbiotic recurrent nova, such as T CrB, are governed by similar mass-transfer mechanisms as found in cataclysmic variables despite their different orbital properties (longer orbital periods imposing larger accretion disks) and evolutionary pathways.

On the Response of Massive Main Sequence Stars to Mass Accretion and Outflow at High Rates

Abstract With a one-dimensional stellar evolution model, we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from their outer layers simultaneously with mass accretion. We assume the accretion process is via an accretion disk that launches powerful jets from its inner zones. These jets remove the outer high-entropy layers of the mass-accreting star. This process operates in a negative feedback cycle, as the jets remove more envelope mass when the star expands. With the one-dimensional model, we mimic the mass removal by jets by alternating mass addition and mass removal phases. For the simulated models of 30M ⊙ and 60M ⊙, the star does not expand much if we remove more than about half of the added mass in not-too-short episodes. This holds even if we deposit the energy the jets do not carry into the envelope. As the star does not expand much, its gravitational potential well stays deep, and the jets are energetic. These results are relevant to bright transient events of binary systems powered by accretion and the launching of jets, e.g., intermediate luminosity optical transients, including some luminous red novae, the grazing envelope evolution, and the 1837–1856 Great Eruption of Eta Carinae.

A Semi-analytical Model for Stellar Evolution in AGN Disks

Abstract Disks of gas accreting onto supermassive black holes may host numerous stellar-mass objects, formed within the disk or captured from a nuclear star cluster. We present a simplified model of stellar evolution in these dense environments, which exhibits exceptional agreement with full stellar evolution calculations at a minuscule fraction of the cost. Although the model presented here is limited to stars burning hydrogen in their cores, it is sufficient to determine the evolutionary fate of disk-embedded stars: whether they proceed to later stages of nuclear burning and leave behind a compact remnant, reach a quasi-steady state where mass loss and accretion balance one another, or whether accretion proceeds faster than stellar structure can adjust, causing a runaway. We highlight how various disk parameters and phenomena such as gap opening affect stellar evolution outcomes. We also highlight how our model can accommodate time-varying conditions, such as those experienced by a star on an eccentric orbit, and can couple to N-body integrations. This model will enable more detailed studies of stellar populations and their interaction with accretion disks than have previously been possible.

H-AMR FORGE’d in FIRE. I. Magnetic State Transitions, Jet Launching, and Radiative Emission in Super-Eddington, Highly Magnetized Quasar Disks Formed from Cosmological Initial Conditions

Abstract Quasars are powered by supermassive black hole (SMBH) accretion disks, yet standard thin disk models are inconsistent with many observations. Recently, P. F. Hopkins et al. simulated the formation of a quasar disk feeding an SMBH of mass M = 1.3 × 107 M ⊙ in a galaxy. The disk had surprisingly strong toroidal magnetic fields that supported it vertically from gravity and powered rapid accretion. What feedback can such a system produce? To answer this, we must follow the gas to the event horizon. For this, we interpolated the quasar into the general-relativistic radiation magnetohydrodynamics code H-AMR and performed 3D simulations with BH spins a = 0 and a = 0.9375. This remapping generates magnetic monopoles, which we erase using a novel divergence cleaning approach. Despite the toroidal magnetic field's dominance at large radii, vertical magnetic flux builds up near the event horizon, leading to a magnetic state transition within the inner 200 gravitational radii of the disk. This powers strong winds and, for spinning BHs, relativistic jets that can spin down the BH within 5−10 Myr. Sometimes, vertical magnetic fields of opposite polarity reach the BH, causing a polarity inversion event that briefly destroys the jets and, possibly, the X-ray corona. These strong fields power accretion at rates 5× the Eddington limit, which can double the BH mass in 5–10 Myr. When a = 0.9375 (a = 0), the energy in mechanical outflows and radiation equals about 60% (10%) and 100% (3%) of the accreted rest mass energy, respectively. Much of the light escapes in cool, ≳1300 au photospheres, consistent with quasar microlensing and spectral energy distributions.

Cyclical accretion regime change in the slow X-ray pulsar 4U 0114+65 observed with Chandra

4U 0114+65 is a high-mass X-ray binary system formed by the luminous supergiant B1Ia, known as V V662 Cas, and one of the slowest rotating neutron stars (NSs) with a spin period of about 2.6 hours. This provides a rare opportunity to study interesting details of the accretion within each individual pulse of the compact object. For this paper we analyzed 200 ks of Chandra grating data, divided into nine uninterrupted observations around the orbit. The changes in the circumstellar absorption column through the orbit suggest an orbital inclination of ∼ 40^∘ with respect to the observer and a companion mass-loss rate of ∼ 8.6 10^-7 M yr^-1. The peaks of the NS pulse exhibit a large pulse-to-pulse variability. Three of them show an evolution from a brighter regime to a weaker one. We propose that the efficiency of Compton cooling in this source fluctuates throughout an accumulation cycle. After significant depletion of matter within the magnetosphere, since the settling velocity is ∼ 2 lower than the free-fall velocity, the source gradually accumulates matter until the density exceeds a critical threshold. This increase in density triggers a transition to a more efficient Compton cooling regime, leading to a higher mass accretion rate and consequently to an increased brightness.

Random Asymmetric Jets Driven by Black-Hole Hyperaccretion in Gamma-Ray Bursts

The relativistic jets of gamma-ray bursts (GRBs) might be powered by a black-hole (BH) hyperaccretion system. The inherent asymmetry in these jets generates recoil forces, inducing oscillations and positional deviations of the BH from equilibrium. In this study, we explore the influence of different initial BH mass, spin, and mass accretion rate, as well as their evolutions on the dynamical properties of BH under the effect of asymmetric jets. Our results reveal that the initial mass and accretion rate significantly impact the BH’s acceleration, velocity, and displacement, while the different initial spin plays a negligible role in shaping the overall dynamical evolution. Additionally, we calculate the gravitational wave (GW) strains associated with the asymmetric jets, finding that the resulting GW signals are too weak to be detected, even for nearby GRBs. These findings provide critical insights into the dynamical response of BHs to asymmetric jets and the associated GW radiation, advancing our understanding of BH physics in GRBs.

Ellipticities of Galaxy Cluster Halos from Halo–Shear–Shear Correlations

Abstract We report the first detection of the halo ellipticities of galaxy clusters by applying the halo–shear–shear correlations (HSSCs), without the necessity of using major axis determination. We use the Fourier_Quad shear catalog based on the Hyper Suprime-Cam Survey and the group catalog from the Dark Energy Spectroscopic Instrument Legacy Surveys for the measurement of group/cluster lensing and HSSC. Our analysis includes off-centering effects. We obtain the average projected ellipticity of dark matter halos with mass 13.5 < log ( M G h / M ⊙ ) < 14.5 within a 1.3 virial radius to be 0.4 8 − 0.19 + 0.12 . We divide the sample into two groups based on mass and redshift, and we find that halos with higher mass tend to exhibit increased ellipticity. We also reveal that high-richness halos have larger ellipticities, confirming the physical picture from numerical simulation that high-richness halos have a dynamical youth and more active mass accretion phase.

Steady-state solutions for a geometrically thin accretion disk with magnetically-driven winds

Abstract We present steady-state solutions for a one-dimensional, magnetically-driven accretion disk wind model based on magnetohydrodynamic equations. We assume a geometrically thin, gas-pressure-dominated accretion disk, incorporating both magnetic braking and turbulent viscosity introduced by an extended alpha-viscosity prescription. Additionally, the vertical stress parameter is assumed to scale with the disk aspect ratio. We confirm that the derived solutions result in standard disk solutions when the wind is absent. We find that the mass accretion rate decreases as the disk mass falls inward, while the mass loss rate increases with radius. The disk spectrum emitted from the magnetically-driven disk wind can be observed without interference from the wind medium because the wind is significantly optically thin. The spectral luminosity is proportional to ν1/3 in the intermediate, multicolor-blackbody wavebands, in the absence of wind, as predicted by standard disk theory. However, in the presence of wind, it follows a different power-law dependence on frequency over the same range. A deviation from the spectral slope of 1/3, particularly a negative spectral slope, is a clear indicator of the presence of a magnetically driven wind. We also discuss an observational strategy to test our model with multi-wavelength observations.

Prediction of Individual Halo Concentrations Across Cosmic Time Using Neural Networks

The concentration of dark matter haloes is closely linked to their mass accretion history. We utilize the halo mass accretion histories from large cosmological N-body simulations as inputs for our neural networks, which we train to predict the concentration of individual haloes at a given redshift. The trained model performs effectively in other cosmological simulations, achieving the root mean square error between the actual and predicted concentrations that significantly lower than that of the model by Zhao et al. and Giocoli et al. at any redshift. This model serves as a valuable tool for rapidly predicting halo concentrations at specified redshifts in large cosmological simulations.

Analyses of Multiple Balmer Emission Lines from Accreting Brown Dwarfs and Very Low Mass Stars

Abstract A planetary growth rate, i.e., the mass accretion rate, is a fundamental parameter in planet formation, as it determines a planet's final mass. Planetary mass accretion rates have been estimated using hydrogen lines, based on the models originally developed for accreting stars, known as the accretion flow model. Recently, Aoyama et al. introduced the accretion shock model as an alternative mechanism for hydrogen line emission. However, it remains unclear which model is more appropriate for accreting planets and substellar objects. To address this, we applied both models to archival data consisting of 96 data points from 76 accreting brown dwarfs and very-low-mass stars, with masses ranging from approximately 0.02 to 0.1 M ⊙, to test which model best explains their accreting properties. The results showed that the emission mechanisms of 15 data points are best explained by the shock model, while 55 data points are best explained by the flow model. For the 15 data points explained by the planetary shock model, the shock model estimates up to several times higher mass accretion rates than the flow model. As this trend is more pronounced for planetary-mass objects, it is crucial to determine which emission mechanism is dominant in individual planets. We also discuss the physical parameters that determine the emission mechanisms and the variability of line ratios.

Eruptive YSOs in Cygnus-X: a mid-infrared variability study with NEOWISE and SPICY

Abstract The mass accretion process controls pre-main-sequence evolution, although its intrinsic instability has yet to be fully understood, especially towards the protostellar stage. In this work, we have undertaken a thorough examination of the mid-infrared variability of Spitzer-selected YSOs in the Cygnus-X star-forming region over the last decade, using the NEOWISE time series. This work compares two groups of young stars: embedded Class I objects, and the more evolved flat-spectrum/Class II sources. We report on 48 candidate eruptive variables within these groups, including 14 with characteristics that resemble the photometric behaviour of FUors. We also include an additional 20 YSOs, which are of a less certain categorisation. We find the candidate FUors to be an order of magnitude more common among the younger Class I systems than more evolved objects. A large number of the identified short-duration eruptive YSOs display mid-infrared colour behaviour that is redder-when-brighter, which contrasts with optically bright outbursts seen in YSOs. Finally, we note the unusual long-term rising behaviours of four Class I YSOs, with rise timescales longer than five years, which is far slower than ∼6-12 month timescale for the majority of optically discovered FUors. Additionally, our broader investigation of MIR variability for embedded class I YSOs shows that there is a higher incidence of high amplitude variability for these stars, than is seen in class II sources. This holds true for all variable class I YSOs, not just the eruptive sources.

Predictions of Dust Continuum Emission from a Potential Circumplanetary Disk: A Case Study of the Planet Candidate AB Aurigae b

Abstract Gas-accreting planets embedded in protoplanetary disks are expected to show dust thermal emission from their circumplanetary disks (CPDs). However, a recently reported gas-accreting planet candidate, AB Aurigae b, has not been detected in (sub)millimeter continuum observations. We calculate the evolution of dust in the potential CPD of AB Aurigae b and predict its thermal emission at 1.3 mm wavelength as a case study, where the obtained features may also be applied to other gas-accreting planets. We find that the expected flux density from the CPD is lower than the 3σ level of the previous continuum observation by the Atacama Large Millimeter/submillimeter Array with broad ranges of parameters, consistent with a nondetection. However, the expected planet mass and gas accretion rate are higher if the reduction of the observed near-infrared continuum and Hα line emission due to the extinction by small grains is considered, resulting in higher flux density of the dust emission from the CPD at (sub)millimeter wavelengths. We find that the corrected predictions of the dust emission are stronger than the 3σ level of the previous observation with the typical dust-to-gas mass ratio of the inflow to the CPD. This result suggests that the dust supply to the vicinity of AB Aurigae b is small if the planet candidate is not the scattered light of the star but is a planet and has a CPD. Future continuum observations at shorter wavelengths are required to obtain more robust clues to the question of whether the candidate is a planet or not.

Consensus evidence-based clinical practice guide for the diagnosis and management of osteoporosis in childhood and adolescence

BackgroundThe incidence of osteoporosis in children has increased dramatically during the last decade. This has been attributed to better survival rates of children living with chronic disorders, the increased use of medications known to have a negative impact on the children’s bones, and the increased preference for indoor activities and sedentary life in healthy children. Recent advances in pediatric osteoporosis definition, along with a lack of management recommendations or national consensus on its diagnosis and treatment, have led to a wide range of approaches being implemented to manage this illness. The aim of this work was to develop an optimal evidence-based consensus, target-oriented, on-steered therapeutic approach for children with osteoporosis. Based on 15 key clinical questions, a qualitative literature evaluation was conducted to provide evidence-based recommendations for the treatment of pediatric osteoporosis. An expert panel of 14 pediatric osteoporosis specialists conducted a Delphi survey. The level of evidence for each element was assessed using the Oxford Centre for Evidence-based Medicine (CEBM) System, when available, and/or based on the expert panel’s personal experience. All recommendations with an agreement rate of 75% or higher were included.ResultsThirty-six recommendations, categorized into 13 domains, had evidence 4 or 5 and consequently were included in the Delphi survey. This was assessed online and a response rate of 82.4% was achieved. Delphi 2 round revealed that all the recommendations achieved 75% or more level of agreement and therefore have been accepted and included in this management recommendations. Based on that an algorithm showing an approach to pediatric osteoporosis management and maintenance of therapy has been developed.ConclusionFor the management of children with osteoporosis, consulting a pediatric bone specialist is strongly advised, either by referral or by advice. This is extremely relevant because children are uniquely capable of recovering spontaneously or with the assistance of medication. This includes also vertebral fractures reshaping. Consequently, there is a huge opportunity to improve bone mass accretion and thus musculoskeletal health in children with osteoporosis.

Impact of radiative cooling on the magnetised geometrically thin accretion disc around Kerr black hole

It is believed that the spectral state transitions of the outbursts in X-ray binaries (XRBs) are triggered by the rise of the mass accretion rate due to underlying disc instabilities. Recent observations found that characteristics of disc winds are probably connected with the different spectral states, but the theoretical underpinnings of it are highly ambiguous. To understand the correlation between disc winds and the dynamics of the accretion flow, we have performed General Relativistic Magneto-hydrodynamic (GRMHD) simulations of an axisymmetric thin accretion disc with different accretion rates and magnetic field strengths.Our simulations have shown that the dynamics and the temperature properties depend on both accretion rates and magnetic field strengths. We later found that these properties greatly influence spectral properties. We calculated the average coronal temperature for different simulation models, which is correlated with high-energy Compton emission. Our simulation models reveal that the average coronal temperature is anti-correlated with the accretion rates, which are correlated with the magnetic field strengths. We also found that the structured component of the disc winds (Blandford-Payne disc wind) predominates as the accretion rates and magnetic field strengths increase. In contrast, the turbulent component of the disc winds (B tor disc wind) predominates as the accretion rates and magnetic field strengths decrease. Our results suggest that the disc winds during an outburst in XRBs can only be understood if the magnetic field contribution varies over time (e.g., MAXI J1820+070).

The Three Hundred project: The relationship between the shock and splashback radii of simulated galaxy clusters

Abstract Observations of the intracluster medium (ICM) in the outskirts of galaxy clusters reveal shocks associated with gas accretion from the cosmic web. Previous work based on non-radiative cosmological hydrodynamical simulations have defined the shock radius, $r_{\text{shock}}$ , using the ICM entropy, $K \propto T/{n_\mathrm{e}}^{2/3}$ , where T and $n_{\text{e}}$ are the ICM temperature and electron density, respectively; the $r_{\text{shock}}$ is identified with either the radius at which K is a maximum or at which its logarithmic slope is a minimum. We investigate the relationship between $r_{\text{shock}}$ , which is driven by gravitational hydrodynamics and shocks, and the splashback radius, $r_{\text{splash}}$ , which is driven by the gravitational dynamics of cluster stars and dark matter and is measured from their mass profile. Using 324 clusters from The Three Hundred project of cosmological galaxy formation simulations, we quantify statistically how $r_{\text{shock}}$ relates to $r_{\text{splash}}$ . Depending on our definition, we find that the median $r_{\text{shock}} \simeq 1.38 r_{\text{splash}} (2.58 R_{200})$ when K reaches its maximum and $r_{\text{shock}} \simeq 1.91 r_{\text{splash}} (3.54 R_{200})$ when its logarithmic slope is a minimum; the best-fit linear relation increases as $r_{\text{shock}} \propto 0.65 r_{\text{splash}}$ . We find that $r_{\text{shock}}/R_{200}$ and $r_{\text{splash}}/R_{200}$ anti-correlate with virial mass, $M_{200}$ , and recent mass accretion history, and $r_{\text{shock}}/r_{\text{splash}}$ tends to be larger for clusters with higher recent accretion rates. We discuss prospects for measuring $r_{\text{shock}}$ observationally and how the relationship between $r_{\text{shock}}$ and $r_{\text{splash}}$ can be used to improve constraints from radio, X-ray, and thermal Sunyaev-Zeldovich surveys that target the interface between the cosmic web and clusters.

Detection of a Highly Ionized Outflow in the Quasiperiodically Erupting Source GSN 069

Quasiperiodic eruptions (QPEs) are high-amplitude, soft X-ray bursts recurring every few hours, associated with supermassive black holes. Many interpretations for QPEs were proposed since their recent discovery in 2019, including extreme mass ratio inspirals and accretion disk instabilities. But, as of today, their nature still remains debated. We perform the first high-resolution X-ray spectral study of a QPE source using the Reflection Grating Spectrometers' gratings on board XMM-Newton, leveraging nearly 2 Ms of exposure on GSN 069, the first discovered source of this class. We resolve several absorption and emission lines including a strong line pair near the N vii rest-frame energy, resembling the P-Cygni profile. We apply photoionization spectral models and identify the absorption lines as an outflow blueshifted by 1700−2900 km s−1, with a column density of about 1022 cm−2 and an ionization parameter log(ξ /erg cm s−1) of 3.9−4.6. The emission lines are instead redshifted by up to 2900 km s−1, and likely originate from the same outflow that imprints the absorption features, and covers the full 4π sky from the point of view of GSN 069. The column density and ionization are comparable to the outflows detected in some tidal disruption events, but this outflow is significantly faster and has a strong emission component. The outflow is more highly ionized when the system is in the phase during which QPEs are present, and from the limits, we derive on its location, we conclude that the outflow is connected to the recent complex, transient activity of GSN 069, which began around 2010.

Filament Accretion and Fragmentation in the Perseus Molecular Cloud

Observations suggest that filaments in molecular clouds can grow by mass accretion while forming cores via fragmentation. Here, we present one of the first large-sample studies of filament accretion using velocity gradient measurements of star-forming filaments on the ∼0.05 pc scale with NH3 observations of the Perseus Molecular Cloud, primarily obtained as a part of the Green Bank Ammonia Survey. In this study, we find significant correlations between the velocity gradient, velocity dispersion, mass per unit length, and number of cores per unit length of the Perseus filaments. Our results suggest a scenario in which filaments not only grow through mass accretion, but also form new cores continuously in the process, well into the thermally supercritical regime. Such behavior is contrary to that expected from isolated filament models but consistent with how filaments form within a more realistic cloud environment, suggesting that the cloud environment plays a crucial role in shaping core formation and evolution in filaments. Furthermore, even though velocity gradients within filaments are not oriented randomly, we find no correlation between velocity gradient orientation and the filament properties we analyzed. This result suggests that gravity is unlikely to be the dominant mechanism imposing order on the ∼0.05 pc scale for dense star-forming gas.

Mass evolution of broad-line regions to explain the luminosity variability of broad Hα in the tidal disruption event ASASSN-14li

We propose an oversimplified model to explain the different variability trends in the observed broad Hα emission line luminosity, LHα(t), and the tidal disruption event (TDE) model-determined bolometric luminosity, Lbol(t), of the TDE ASASSN-14li. Assuming that broad emission line regions (BLRs) in the central accretion disk are related to materials accreted onto the central black hole of a TDE, the mass evolution of central BLRs, MBLRs(t), can be determined as the maximum mass, MBLRs, 0, of central BLRs minus the corresponding accreted mass in a TDE. Meanwhile, through the simple linear dependence of broad Balmer emission line luminosity on the mass of BLRs, the mass evolution of central BLRs, MBLRs(t), can be applied to describe the observed LHα(t). Although our proposed model is oversimplified – with only one free model parameter, MBLRs, 0 – with MBLRs, 0 ∼ 0.02 M⊙, it describes the observed LHα(t) in the TDE ASASSN-14li well. Meanwhile, the oversimplified model also roughly describes the observed LHα(t) in the TDE ASASSN-14ae. The reasonable descriptions of the observed LHα(t) in ASASSN-14li and ASASSN-14ae indicate that our oversimplified model is probably efficient enough to describe mass evolutions of MBLRs related to central accreted debris in TDEs.