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Journal articles on the topic 'Accretion discs'

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Author: Grafiati

Published: 4 June 2021

Last updated: 7 September 2023

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1

Joshi, Gandhali D., Annalisa Pillepich, Dylan Nelson, Federico Marinacci, Volker Springel, Vicente Rodriguez-Gomez, Mark Vogelsberger, and Lars Hernquist. "The fate of disc galaxies in IllustrisTNG clusters." Monthly Notices of the Royal Astronomical Society 496, no. 3 (June 12, 2020): 2673–703. http://dx.doi.org/10.1093/mnras/staa1668.

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ABSTRACT We study the stellar morphological evolution of disc galaxies within clusters in the TNG50 and TNG100 runs from the IllustrisTNG simulation suite. We select satellites of masses 109.7 ≤ M*, z = 0/M⊙ ≤ 1011.6 residing in clusters of masses 1014 ≲ M200c, z = 0/M⊙ ≤ 1014.6 at z = 0 and that were discs at accretion according to a kinematic morphology indicator (the circularity fraction). These are traced from the time of accretion to z = 0 and compared to a control sample of central galaxies mass-matched at accretion. Most cluster discs become non-discy by z = 0, in stark contrast with the control discs, of which a significant fraction remains discy over the same timescales. Cluster discs become non-discy accompanied by gas removal and star formation quenching, loss of dark matter, and little growth or a loss of stellar mass. In contrast, control discs transform while also losing gas mass and quenching, but growing significantly in dark matter and stellar mass. Most cluster satellites change morphologies on similar timescales regardless of stellar mass, in ∼0.5–4 Gyr after accretion. Cluster discs that experienced more numerous and closer pericentric passages show the largest change in morphology. Morphological change in all cases requires the presence of a gravitational perturbation to drive stellar orbits to non-discy configurations, along with gas removal/heating to prevent replenishment of the disc through continued star formation. For cluster discs, the perturbation is impulsive tidal shocking at pericentres and not tidal stripping of outer disc stellar material, whereas for control discs, a combination of mergers and feedback from active galactic nuclei appears to be the key driving force behind morphological transformations.

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2

Abramowicz, Marek, and Odele Straub. "Accretion discs." Scholarpedia 9, no. 8 (2014): 2408. http://dx.doi.org/10.4249/scholarpedia.2408.

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3

Hameury, J. M., and J. P. Lasota. "Models of ultraluminous X-ray transient sources." Astronomy & Astrophysics 643 (November 2020): A171. http://dx.doi.org/10.1051/0004-6361/202038857.

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Context. It is now widely accepted that most ultraluminous X-ray sources (ULXs) are binary systems whose large (above 1039 erg s−1) apparent luminosities are explained by super-Eddington accretion onto a stellar-mass compact object. Many of the ULXs, especially those containing magnetized neutron stars, are highly variable; some exhibit transient behaviour. Large luminosities might imply large accretion discs that could be therefore prone to the thermal–viscous instability known to drive outbursts of dwarf novae and low-mass X-ray binary transient sources. Aims. The aim of this paper is to extend and generalize the X-ray transient disc-instability model to the case of large (outer radius larger than 1012 cm) accretion discs and apply it to the description of systems with super-Eddington accretion rates at outburst and, in some cases, super-Eddington mass transfer rates. Methods. We have used our disc-instability-model code to calculate the time evolution of the accretion disc and the outburst properties. Results. We show that, provided that self-irradiation of the accretion disc is efficient even when the accretion rate exceeds the Eddington value, possibly due to scattering back of the X-ray flux emitted by the central parts of the disc on the outer portions of the disc, heating fronts can reach the disc’s outer edge generating high accretion rates. We also provide analytical approximations for the observable properties of the outbursts. We have successfully reproduced the observed properties of galactic transients with large discs, such as V404 Cyg, as well as some ULXs such as M51 XT-1. Our model can reproduce the peak luminosity and decay time of ESO 243-39 HLX-1 outbursts if the accretor is a neutron star. Conclusions. Observational tests of our predicted relations between the outburst duration and decay time with peak luminosity would be most welcome.

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Vogel, M. "Photoionization models with accretion discs." International Astronomical Union Colloquium 103 (1988): 119–21. http://dx.doi.org/10.1017/s0252921100103252.

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AbstractThe diagnositic possibilities for identifying the ionizing source in symbiotic systems are explored. As possible sources we consider hot blackbodies and accretion discs. It turns out that main sequence accretors and hot blackbodies may have the same appearance in both, emission line and continuum flux distribution. However, UV continuum indices of models containing an accretion disc around a white dwarf are confined to a very small region, separated from main sequence accretors and blackbodies. Furthermore, if symbiotic systems containing a white dwarf accretor exist, they might be recognizable by strong emission in Fe X λ6374.

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Fraternali, Filippo, and Gabriele Pezzulli. "Angular Momentum Accretion onto Disc Galaxies." Proceedings of the International Astronomical Union 14, A30 (August 2018): 228–32. http://dx.doi.org/10.1017/s1743921319004125.

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AbstractThroughout the Hubble time, gas makes its way from the intergalactic medium into galaxies fuelling their star formation and promoting their growth. One of the key properties of the accreting gas is its angular momentum, which has profound implications for the evolution of, in particular, disc galaxies. Here, we discuss how to infer the angular momentum of the accreting gas using observations of present-day galaxy discs. We first summarize evidence for ongoing inside-out growth of star forming discs. We then focus on the chemistry of the discs and show how the observed metallicity gradients can be explained if gas accretes onto a disc rotating with a velocity 20 – 30% lower than the local circular speed. We also show that these gradients are incompatible with accretion occurring at the edge of the discs and flowing radially inward. Finally, we investigate gas accretion from a hot corona with a cosmological angular momentum distribution and describe how simple models of rotating coronae guarantee the inside-out growth of disc galaxies.

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6

Hure, J. M., and D. Richard. "Accretion Discs in AGN, Viscosity and Structure of Accretion Disks." EAS Publications Series 1 (2001): 53–61. http://dx.doi.org/10.1051/eas:2001008.

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7

Ginzburg, Sivan, and Eugene Chiang. "The endgame of gas giant formation: accretion luminosity and contraction post-runaway." Monthly Notices of the Royal Astronomical Society 490, no. 3 (October 16, 2019): 4334–43. http://dx.doi.org/10.1093/mnras/stz2901.

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ABSTRACT Giant planets are thought to form by runaway gas accretion on to solid cores. Growth must eventually stop running away, ostensibly because planets open gaps (annular cavities) in their surrounding discs. Typical models stop runaway by artificially capping the accretion rate and lowering it to zero over an arbitrarily short time-scale. In reality, post-runaway accretion persists as long as the disc remains. During this final and possibly longest phase of formation, when the planet is still emerging from the disc, its mass can more than double, and its radius contracts by orders of magnitude. By drawing from the theory of how gaps clear, we find that post-runaway accretion luminosities diverge depending on disc viscosity: luminosities fall in low-viscosity discs but continue to rise past runaway in high-viscosity discs. This divergence amounts to a factor of 102 by the time the disc disperses. Irrespective of the specifics of how planets interact with discs, the observed luminosity and age of an accreting planet can be used to calculate its instantaneous mass, radius, and accretion rate. We perform this exercise for the planet candidates embedded within the discs orbiting PDS 70, HD 163296, and MWC 758, inferring masses of 1–10 MJ, accretion rates of 0.1–10 MJ Myr−1, and radii of 1–10 RJ. Our radii are computed self-consistently from the planet’s concurrent contraction and accretion and do not necessarily equal the value of 2RJ commonly assumed; in particular, the radius depends on the envelope opacity as R ∝ κ0.5.

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8

Lyubarskij, Yu E., K. A. Postnov, and M. E. Prokhorov. "Eccentric accretion discs." Monthly Notices of the Royal Astronomical Society 266, no. 3 (February 1994): 583–96. http://dx.doi.org/10.1093/mnras/266.3.583.

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9

Chakrabarty, D., J. Murray, G. A. Wynn, and A. R. King. "Warped Accretion Discs." Symposium - International Astronomical Union 208 (2003): 385–86. http://dx.doi.org/10.1017/s0074180900207389.

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In this article we report the results of our numerical investigation of warped accretion discs in binary stellar systems. We perform complete 3-D hydrodynamic simulations of binary discs. The disc is rendered unstable to the warp mode under the action of the magnetic field of the companion star in the binary. The disc thus warped is noted to undergo retrograde precession with a precession period just slightly less than the binary period. This small difference in periods can explain the phenomenon of negative superhumps observed in a number of binaries. Besides the modal analysis based on Fourier transforms, warps were also studied by a simple and robust technique that we developed; this is based on an analysis of the azimuthal distributions of particles that lie above and below the mid-plane of the disc.

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BOGOVALOV, S. V., and S. R. KELNER. "ACCRETION AND PLASMA OUTFLOW FROM DISSIPATIONLESS DISCS." International Journal of Modern Physics D 19, no. 03 (March 2010): 339–65. http://dx.doi.org/10.1142/s0218271810016373.

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We consider the specific case of disc accretion for negligibly low viscosity and infinitely high electric conductivity. The key component in this model is the outflowing magnetized wind from the accretion disc, since this wind effectively carries away angular momentum of the accreting matter. Assuming magnetic field has variable polarity in the disc (to avoid magnetic flux and energy accumulation at the gravitational center), this leads to radiatively inefficient accretion of the disc matter onto the gravitational center. In such a case, the wind forms an outflow, which carries away all the energy and angular momentum of the accreted matter. Interestingly, in this framework, the basic properties of the outflow (as well as angular momentum and energy flux per particle in the outflow) do not depend on the structure of accretion disc. The self-similar solutions obtained prove the existence of such an accreting regime. In the self-similar case, the disc accretion rate (Ṁ) depends on the distance to the gravitational center, r, as [Formula: see text], where λ is the dimensionless Alfvenic radius. Thus, the outflow predominantly occurs from the very central part of the disc provided that λ ≫ 1 (it follows from the conservation of matter). The accretion/outflow mechanism provides transformation of the gravitational energy from the accreted matter into the energy of the outflowing wind with efficiency close to 100%. The flow velocity can essentially exceed the Kepler velocity at the site of the wind launch.

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Lega, E., A. Morbidelli, R. P. Nelson, X. S. Ramos, A. Crida, W. Béthune, and K. Batygin. "Migration of Jupiter mass planets in discs with laminar accretion flows." Astronomy & Astrophysics 658 (January 27, 2022): A32. http://dx.doi.org/10.1051/0004-6361/202141675.

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Context. Migration of giant planets in discs with low viscosity has been studied recently. Results have shown that the proportionality between migration speed and the disc’s viscosity is broken by the presence of vortices that appear at the edges of the planet-induced gap. Under some conditions, this ‘vortex-driven’ migration can be very slow and eventually stops. However, this result has been obtained for discs whose radial mass transport is too low (due to the small viscosity) to be compatible with the mass accretion rates that are typically observed for young stars. Aims. Our goal is to investigate vortex-driven migration in low-viscosity discs in the presence of radial advection of gas, as expected from angular momentum removal by magnetised disc winds. Methods. We performed three dimensional simulations using the grid-based code FARGOCA. We mimicked the effects of a disc wind by applying a synthetic torque on a surface layer of the disc characterised by a prescribed column density ΣA so that it results in a disc accretion rate of ṀA = 10−8 M⊙ yr−1. We have considered values of ΣA typical of the penetration depths of different ionising processes. Discs with this structure are called ‘layered’ and the layer where the torque is applied is denoted as ‘active’. We also consider the case of accretion focussed near the disc midplane to mimic transport properties induced by a large Hall effect or by weak Ohmic diffusion. Results. We observe two migration phases: in the first phase, which is exhibited by all simulations, the migration of the planet is driven by the vortex and is directed inwards. This phase ends when the vortex disappears after having opened a secondary gap, as is typically observed in vortex-driven migration. Migration in the second phase depends on the ability of the torque from the planet to block the accretion flow. When the flow is fast and unimpeded, corresponding to small ΣA, migration is very slow, similar to when there is no accreting layer in the disc. When the accretion flow is completely blocked, migration is faster (typically ṙp ~ 12 AU Myr−1 at 5 au) and the speed is controlled by the rate at which the accretion flow refills the gap behind the migrating planet. The transition between the two regimes, occurs at ΣA ~ 0.2 g cm−2 and 0.65 g cm−2 for Jupiter or Saturn mass planets at 5.2 au, respectively. Conclusions. The migration speed of a giant planet in a layered protoplanetary disc depends on the thickness of the accreting layer. The lack of large-scale migration apparently experienced by the majority of giant exoplanets can be explained if the accreting layer is sufficiently thin to allow unimpeded accretion through the disc.

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12

Tout, Christopher A. "Accretion Disc Viscosity." International Astronomical Union Colloquium 158 (1996): 97–106. http://dx.doi.org/10.1017/s0252921100038343.

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AbstractWe review the various physical processes that could lead to viscosity in accretion discs. A local magnetic dynamo offers the most plausible mechanism and we discuss a simple model in some detail. The dynamo operates even in partially and very weakly ionized discs without much modification.

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13

Nixon, Christopher J., and Andrew R. King. "Broken discs: warp propagation in accretion discs." Monthly Notices of the Royal Astronomical Society 421, no. 2 (February 21, 2012): 1201–8. http://dx.doi.org/10.1111/j.1365-2966.2011.20377.x.

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Noguchi, Masafumi. "Structural diversity of disc galaxies originating in the cold gas inflow from cosmic webs." Monthly Notices of the Royal Astronomical Society: Letters 494, no. 1 (February 10, 2020): L37—L41. http://dx.doi.org/10.1093/mnrasl/slaa017.

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ABSTRACT Disc galaxies show a large morphological diversity with varying contribution of three major structural components: thin discs, thick discs, and central bulges. Dominance of bulges increases with the galaxy mass (Hubble sequence), whereas thick discs are more prominent in lower mass galaxies. Because galaxies grow with the accretion of matter, this observed variety should reflect diversity in accretion history. On the basis of the prediction by the cold-flow theory for galactic gas accretion and inspired by the results of previous studies, we put a hypothesis that associates different accretion modes with different components. Namely, thin discs form as the shock-heated hot gas in high-mass haloes gradually accretes to the central part, thick discs grow by the direct accretion of cold gas from cosmic webs when the halo mass is low, and finally bulges form by the inflow of cold gas through the shock-heated gas in high-redshift massive haloes. We show that this simple hypothesis reproduces the mean observed variation of galaxy morphology with the galaxy mass. This scenario also predicts that thick discs are older and poorer in metals than thin discs, in agreement with the currently available observations.

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Yuan, F. "Luminous hot accretion discs." Monthly Notices of the Royal Astronomical Society 324, no. 1 (June 1, 2001): 119–27. http://dx.doi.org/10.1046/j.1365-8711.2001.04258.x.

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16

Idan, I., and G. Shaviv. "Winds from accretion discs." Monthly Notices of the Royal Astronomical Society 281, no. 2 (July 11, 1996): 615–25. http://dx.doi.org/10.1093/mnras/281.2.615.

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Jolley, E. J. D., Z. Kuncic, G. V. Bicknell, and S. Wagner. "Accretion discs in blazars." Monthly Notices of the Royal Astronomical Society 400, no. 3 (December 11, 2009): 1521–26. http://dx.doi.org/10.1111/j.1365-2966.2009.15554.x.

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18

Pudritz, Ralph E. "Jets from accretion discs." Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences 358, no. 1767 (February 15, 2000): 741–58. http://dx.doi.org/10.1098/rsta.2000.0556.

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Dyda, S., R. V. E. Lovelace, G. V. Ustyugova, M. M. Romanova, and A. V. Koldoba. "Counter-rotating accretion discs." Monthly Notices of the Royal Astronomical Society 446, no. 1 (November 11, 2014): 613–21. http://dx.doi.org/10.1093/mnras/stu2131.

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20

Pringle, James E. "5. Atmospheres of Accretion Discs." Transactions of the International Astronomical Union 19, no. 1 (1985): 515–19. http://dx.doi.org/10.1017/s0251107x00006593.

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Accretion discs are a popular ingredient among theorists for modelling a number of high energy astronomical objects like quasars, active galactic nuclei (Rees 1984) and galactic X-ray sources (Levin and van der Heuvel 1983). However, the observational evidence (as opposed to the strong theoretical presumption) that accretion discs exist in these objects is weak, and in only one case has some attempt been made to argue the case for a disc on the basis of its spectral properties (Malkan 1983). Indeed the structure of accretion discs is sufficiently ill-understood that any progress in this area must rest on a strong interaction between theoretical modelling and the actual observation of accretion discs in action.

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Bergez-Casalou, C., B. Bitsch, A. Pierens, A. Crida, and S. N. Raymond. "Influence of planetary gas accretion on the shape and depth of gaps in protoplanetary discs." Astronomy & Astrophysics 643 (November 2020): A133. http://dx.doi.org/10.1051/0004-6361/202038304.

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It is widely known that giant planets have the capacity to open deep gaps in their natal gaseous protoplanetary discs. It is unclear, however, how gas accretion onto growing planets influences the shape and depth of their growing gaps. We performed isothermal hydrodynamical simulations with the Fargo-2D1D code, which assumes planets accreting gas within full discs that range from 0.1 to 260 AU. The gas accretion routine uses a sink cell approach, in which different accretion rates are used to cope with the broad range of gas accretion rates cited in the literature. We find that the planetary gas accretion rate increases for larger disc aspect ratios and greater viscosities. Our main results show that gas accretion has an important impact on the gap-opening mass: we find that when the disc responds slowly to a change in planetary mass (i.e., at low viscosity), the gap-opening mass scales with the planetary accretion rate, with a higher gas accretion rate resulting in a larger gap-opening mass. On the other hand, if the disc response time is short (i.e., at high viscosity), then gas accretion helps the planet carve a deep gap. As a consequence, higher planetary gas accretion rates result in smaller gap-opening masses. Our results have important implications for the derivation of planet masses from disc observations: depending on the planetary gas accretion rate, the derived masses from ALMA observations might be off by up to a factor of two. We discuss the consequences of the change in the gap-opening mass on the evolution of planetary systems based on the example of the grand tack scenario. Planetary gas accretion also impacts stellar gas accretion, where the influence is minimal due to the presence of a gas-accreting planet.

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Di Bernardo, Giuseppe, and Ulf Torkelsson. "Wave modes from the magnetorotational instability in accretion discs." Proceedings of the International Astronomical Union 8, S290 (August 2012): 201–2. http://dx.doi.org/10.1017/s1743921312019618.

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AbstractThe magnetorotational instability (MRI) is widely believed to be the source of turbulence in accretion discs. This turbulence is responsible for the anomalous angular momentum transport in accretion discs. The turbulence will affect other aspects of the dynamics of the disc as well, and we will concentrate on two such issues: a) what kind of oscillations can be excited by the turbulence itself, and b) how the turbulence is interacting with modes that have been excited by some other agent. This is of interest in understanding the quasi-periodic oscillations (QPOs) that have been observed in the X-ray light curves of accreting neutron star and black hole binaries. We carry out local three dimensional (3D) magnetohydrodynamic simulations of a keplerian differentially rotating accretion disc, using a shearing box configuration taking in account the effects of the vertical stratification.

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Coleman, Matthew S. B., Roman R. Rafikov, and Alexander A. Philippov. "Boundary layers of accretion discs: wave-driven transport and disc evolution." Monthly Notices of the Royal Astronomical Society 512, no. 2 (March 22, 2022): 2945–60. http://dx.doi.org/10.1093/mnras/stac732.

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ABSTRACT Astrophysical objects possessing a material surface (white dwarfs, young stars, etc.) may accrete gas from the disc through the so-called surface boundary layer (BL), in which the angular velocity of the accreting gas experiences a sharp drop. Acoustic waves excited by the supersonic shear in the BL play an important role in mediating the angular momentum and mass transport through that region. Here we examine the characteristics of the angular momentum transport produced by the different types of wave modes emerging in the inner disc, using the results of a large suite of hydrodynamic simulations of the BLs. We provide a comparative analysis of the transport properties of different modes across the range of relevant disc parameters. In particular, we identify the types of modes that are responsible for the mass accretion on to the central object. We find the correlated perturbations of surface density and radial velocity to provide an important contribution to the mass accretion rate. Although the wave-driven transport is intrinsically non-local, we do observe a clear correlation between the angular momentum flux injected into the disc by the waves and the mass accretion rate through the BL. We find the efficiency of angular momentum transport (normalized by thermal pressure) to be a weak function of the flow Mach number. We also quantify the wave-driven evolution of the inner disc, in particular the modification of the angular frequency profile in the disc. Our results pave the way for understanding wave-mediated transport in future three-dimensional, magnetohydrodynamic studies of the BLs.

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Coleman, Gavin A. L., and Thomas J. Haworth. "Peter Pan discs: finding Neverland’s parameters." Monthly Notices of the Royal Astronomical Society: Letters 496, no. 1 (June 11, 2020): L111—L115. http://dx.doi.org/10.1093/mnrasl/slaa098.

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ABSTRACT Peter Pan discs are a recently discovered class of long-lived discs around low-mass stars that survive for an order of magnitude longer than typical discs. In this paper, we use disc evolutionary models to determine the required balance between initial conditions and the magnitude of dispersal processes for Peter Pan discs to be primordial. We find that we require low transport (α ∼ 10−4), extremely low external photoevaporation (${\le}10^{-9}\, {\rm M}_{\odot }\, {\rm yr^{-1}}$), and relatively high disc masses (>0.25M*) to produce discs with ages and accretion rates consistent with Peter Pan discs. Higher transport (α = 10−3) results in disc lifetimes that are too short and even lower transport (α = 10−5) leads to accretion rates smaller than those observed. The required external photoevaporation rates are so low that primordial Peter Pan discs will have formed in rare environments on the periphery of low-mass star-forming regions, or deeply embedded, and as such have never subsequently been exposed to higher amounts of UV radiation. Given that such an external photoevaporation scenario is rare, the required disc parameters and accretion properties may reflect the initial conditions and accretion rates of a much larger fraction of the discs around low-mass stars.

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Whitehurst, Robert. "Numerical simulations of accretion discs – I. Superhumps: a tidal phenomenon of accretion discs." Monthly Notices of the Royal Astronomical Society 232, no. 1 (May 1988): 35–51. http://dx.doi.org/10.1093/mnras/232.1.35.

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Wehrse, Rainer. "Accretion Discs around Black Holes." International Astronomical Union Colloquium 163 (1997): 162–72. http://dx.doi.org/10.1017/s0252921100042603.

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AbstractThe structure of accretion discs around (super-)massive black holes is discussed in this contribution with special emphasis on the radiation fields. These are of crucial importance for the understanding of these objects since photons control in most cases not only the temperature distributions but also the pressures and shapes. Recent progress in the modelling of photon fields now provides the means for a much improved understanding of the consequences of the multidimensional structure of the discs as well as of the effects of the strong space time curvature and of the high velocities involved. However, the simultaneous inclusion of the NLTE level populations and of many spectral lines is still a major problem. It is also demonstrated that special and general relativity effects strongly distort the apparent brightness distributions and spectra such accretion discs so that a solution of the inverse problem will be very difficult.

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Toscani, Martina, Giuseppe Lodato, and Rebecca Nealon. "Gravitational wave emission from unstable accretion discs in tidal disruption events." Monthly Notices of the Royal Astronomical Society 489, no. 1 (August 13, 2019): 699–706. http://dx.doi.org/10.1093/mnras/stz2201.

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Abstract Gravitational waves can be emitted by accretion discs if they undergo instabilities that generate a time varying mass quadrupole. In this work we investigate the gravitational signal generated by a thick accretion disc of 1 M⊙ around a static supermassive black hole of 106 M⊙, assumed to be formed after the tidal disruption of a solar type star. This torus has been shown to be unstable to a global non-axisymmetric hydrodynamic instability, the Papaloizou–Pringle instability, in the case where it is not already accreting and has a weak magnetic field. We start by deriving analytical estimates of the maximum amplitude of the gravitational wave signal, with the aim to establish its detectability by the Laser Interferometer Space Antenna (LISA). Then, we compare these estimates with those obtained through a numerical simulation of the torus, made with a 3D smoothed particle hydrodynamics code. Our numerical analysis shows that the measured strain is two orders of magnitude lower than the maximum value obtained analytically. However, accretion discs affected by the Papaloizou–Pringle instability may still be interesting sources for LISA, if we consider discs generated after deeply penetrating tidal disruptions of main-sequence stars of higher mass.

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Hogg, M. A., R. Cutter, and G. A. Wynn. "The effect of a magnetic field on the dynamics of debris discs around white dwarfs." Monthly Notices of the Royal Astronomical Society 500, no. 3 (October 29, 2020): 2986–3001. http://dx.doi.org/10.1093/mnras/staa3316.

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ABSTRACT Observational estimates of the lifetimes and inferred accretion rates from debris discs around polluted white dwarfs are often inconsistent with the predictions of models of shielded Poynting–Robertson drag on the dust particles in the discs. Moreover, many cool polluted white dwarfs do not show any observational evidence of accompanying discs. This may be explained, in part, if the debris discs had shorter lifetimes and higher accretion rates than predicted by Poynting–Robertson drag alone. We consider the role of a magnetic field on tidally disrupted diamagnetic debris and its subsequent effect on the formation, evolution, and accretion rate of a debris disc. We estimate that magnetic field strengths greater than ∼10 kG may decrease the time needed for circularization and the disc lifetimes by several orders of magnitude and increase the associated accretion rates by a similar factor, relative to Poynting–Robertson drag. We suggest some polluted white dwarfs may host magnetic fields below the typical detectable limit and that these fields may account for a proportion of polluted white dwarfs with missing debris discs. We also suggest that diamagnetic drag may account for the higher accretion rate estimates among polluted white dwarfs that cannot be predicted solely by Poynting–Robertson drag and find a dependence on magnetic field strength, orbital pericentre distance, and particle size on predicted disc lifetimes and accretion rates.

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Salmon, J., and R. M. Canup. "Accretion of the Moon from non-canonical discs." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2024 (September 13, 2014): 20130256. http://dx.doi.org/10.1098/rsta.2013.0256.

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Impacts that leave the Earth–Moon system with a large excess in angular momentum have recently been advocated as a means of generating a protolunar disc with a composition that is nearly identical to that of the Earth's mantle. We here investigate the accretion of the Moon from discs generated by such ‘non-canonical’ impacts, which are typically more compact than discs produced by canonical impacts and have a higher fraction of their mass initially located inside the Roche limit. Our model predicts a similar overall accretional history for both canonical and non-canonical discs, with the Moon forming in three consecutive steps over hundreds of years. However, we find that, to yield a lunar-mass Moon, the more compact non-canonical discs must initially be more massive than implied by prior estimates, and only a few of the discs produced by impact simulations to date appear to meet this condition. Non-canonical impacts require that capture of the Moon into the evection resonance with the Sun reduced the Earth–Moon angular momentum by a factor of 2 or more. We find that the Moon's semi-major axis at the end of its accretion is approximately 7 R ⊕ , which is comparable to the location of the evection resonance for a post-impact Earth with a 2.5 h rotation period in the absence of a disc. Thus, the dynamics of the Moon's assembly may directly affect its ability to be captured into the resonance.

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Kley, Wilhelm, Giovanni Picogna, and Moritz H. R. Stoll. "Pebble accretion onto planets in turbulent discs." Proceedings of the International Astronomical Union 14, S345 (August 2018): 237–38. http://dx.doi.org/10.1017/s1743921318008256.

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AbstractPlanets form in protoplanetary accretion discs around young protostars. These discs are driven by internal turbulence and the gas flow is not laminar but has stochastic components. For weakly ionised discs the turbulence can be generated purely hydrodynamically through the vertical shear instability (VSI). Embedded particles (dust/pebbles) experience a hydrodynamic drag and drift inward radially and are stirred up vertically by the turbulent motion of the disc. We study the accretion of particles onto a forming planet embedded in a VSI turbulent protoplanetary disc through a series of 3D hydrodynamical simulations for locally isothermal discs with embedded planets in the mass range from 5 to 100 Earth masses (M2295).

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Held, Loren E., and Henrik N. Latter. "Magnetohydrodynamic convection in accretion discs." Monthly Notices of the Royal Astronomical Society 504, no. 2 (April 12, 2021): 2940–60. http://dx.doi.org/10.1093/mnras/stab974.

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ABSTRACT Convection has been discussed in the field of accretion discs for several decades, both as a means of angular momentum transport and also because of its role in controlling discs’ vertical structure via heat transport. If the gas is sufficiently ionized and threaded by a weak magnetic field, convection might interact in non-trivial ways with the magnetorotational instability (MRI). Recently, vertically stratified local simulations of the MRI have reported considerable variation in the angular momentum transport, as measured by the stress to thermal pressure ratio α, when convection is thought to be present. Although MRI turbulence can act as a heat source for convection, it is not clear how the two instabilities will interact dynamically. Here, we investigate their interplay in controlled numerical experiments and isolate the generic features of their interactions. We perform vertically stratified, 3D magnetohydrodynamic shearing box simulations with a perfect gas equation of state with the conservative, finite-volume code pluto. We find two characteristic outcomes of the interaction between the two instabilities: (a) straight MRI and (b) MRI/convective cycles, with the latter exhibiting alternating phases of convection-dominated and MRI-dominated flow. During the latter phase, we find that α is enhanced by nearly an order of magnitude, reaching peak values of ∼0.08. In addition, we find that convection in the non-linear phase takes the form of large-scale and oscillatory convective cells. Convection can also help the MRI persist to lower Rm than it would otherwise do. Finally, we discuss how our results help interpret simulations of dwarf novae.

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Chen, X. "Hot accretion discs with advection." Monthly Notices of the Royal Astronomical Society 275, no. 3 (August 1, 1995): 641–48. http://dx.doi.org/10.1093/mnras/275.3.641.

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Jaroszy ski, M. "Oscillations of thick accretion discs." Monthly Notices of the Royal Astronomical Society 220, no. 4 (June 1, 1986): 869–81. http://dx.doi.org/10.1093/mnras/220.4.869.

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Whitehurst, Robert, and Andrew King. "Superhumps, resonances and accretion discs." Monthly Notices of the Royal Astronomical Society 249, no. 1 (March 1991): 25–35. http://dx.doi.org/10.1093/mnras/249.1.25.

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Gammie, C. F. "Photon bubbles in accretion discs." Monthly Notices of the Royal Astronomical Society 297, no. 3 (July 1, 1998): 929–35. http://dx.doi.org/10.1046/j.1365-8711.1998.01571.x.

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King, A. R. "Outbursts of irradiated accretion discs." Monthly Notices of the Royal Astronomical Society 296, no. 4 (June 1998): L45—L50. http://dx.doi.org/10.1046/j.1365-8711.1998.01652.x.

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Godon, Patrick, Mario Livio, and Steve Lubow. "Spiral shocks in accretion discs." Monthly Notices of the Royal Astronomical Society 295, no. 1 (March 1998): l11—l14. http://dx.doi.org/10.1046/j.1365-8711.1998.29510584.x.

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Lyubarskii, Y. E. "Flicker noise in accretion discs." Monthly Notices of the Royal Astronomical Society 292, no. 3 (December 11, 1997): 679–85. http://dx.doi.org/10.1093/mnras/292.3.679.

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D’Angelo, Caroline R., and Hendrik C. Spruit. "Accretion discs trapped near corotation." Monthly Notices of the Royal Astronomical Society 420, no. 1 (November 28, 2011): 416–29. http://dx.doi.org/10.1111/j.1365-2966.2011.20046.x.

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Roy, Nirupam, and Arnab K. Ray. "Fractal features in accretion discs." Monthly Notices of the Royal Astronomical Society 397, no. 3 (August 11, 2009): 1374–85. http://dx.doi.org/10.1111/j.1365-2966.2009.14827.x.

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Torkelsson, U., A. Brandenburg, Å. Nordlund, and R. F. Stein. "Magnetohydrodynamic Turbulence in Accretion Discs." Symposium - International Astronomical Union 195 (2000): 241–42. http://dx.doi.org/10.1017/s0074180900162989.

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We present results from numerical simulations of magneto-hydrodynamic turbulence in accretion discs. Our simulations show that the turbulent stresses that drive the accretion are less stratified than the matter; thus, the surface layers are more strongly heated than the interior of the disc.

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Mayer, M., and W. J. Duschl. "Stationary Population III accretion discs." Monthly Notices of the Royal Astronomical Society 356, no. 1 (January 1, 2005): 1–11. http://dx.doi.org/10.1111/j.1365-2966.2004.08426.x.

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Zhen-Yi, Cai, Gu Wei-Min, and Lu Ju-Fu. "Constraints on Slim Accretion Discs." Chinese Physics Letters 25, no. 4 (April 2008): 1514–16. http://dx.doi.org/10.1088/0256-307x/25/4/094.

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Stanley, Q. "Overstable oscillations in accretion discs." Advances in Space Research 8, no. 2-3 (January 1988): 113–18. http://dx.doi.org/10.1016/0273-1177(88)90393-6.

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BISNOVATYI-KOGAN, G. S. "Accretion Discs Around Nonmagnetized Stars*." Annals of the New York Academy of Sciences 759, no. 1 (September 1995): 340–43. http://dx.doi.org/10.1111/j.1749-6632.1995.tb17559.x.

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Tremaine, Scott, and Shane W. Davis. "Dynamics of warped accretion discs." Monthly Notices of the Royal Astronomical Society 441, no. 2 (May 8, 2014): 1408–34. http://dx.doi.org/10.1093/mnras/stu663.

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Amin, M. A., and A. V. Frolov. "Persistent patterns in accretion discs." Monthly Notices of the Royal Astronomical Society: Letters 370, no. 1 (July 1, 2006): L42—L45. http://dx.doi.org/10.1111/j.1745-3933.2006.00185.x.

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Shchekinov, Yuri. "Weakly mass-loaded accretion discs." Astronomical & Astrophysical Transactions 22, no. 1 (February 2003): 81–93. http://dx.doi.org/10.1080/1055679031000079610.

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Bhaskaran, P., and V. Krishan. "Kinetic equilibria of accretion discs." Astrophysics and Space Science 232, no. 1 (1995): 65–78. http://dx.doi.org/10.1007/bf00627544.

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Zanazzi, J. J., and Dong Lai. "Tidal disruption event discs around supermassive black holes: disc warp and inclination evolution." Monthly Notices of the Royal Astronomical Society 487, no. 4 (June 11, 2019): 4965–84. http://dx.doi.org/10.1093/mnras/stz1610.

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ABSTRACT After the tidal disruption event (TDE) of a star around a supermassive black hole (SMBH), the bound stellar debris rapidly forms an accretion disc. If the accretion disc is not aligned with the spinning SMBH’s equatorial plane, the disc will be driven into Lense–Thirring precession around the SMBH’s spin axis, possibly affecting the TDE’s light curve. We carry out an eigenmode analysis of such a disc to understand how the disc’s warp structure, precession, and inclination evolution are influenced by the disc’s and SMBH’s properties. We find an oscillatory warp may develop as a result of strong non-Keplarian motion near the SMBH. The global disc precession frequency matches the Lense–Thirring precession frequency of a rigid disc around a spinning black hole within a factor of a few when the disc’s accretion rate is high, but deviates significantly at low accretion rates. Viscosity aligns the disc with the SMBH’s equatorial plane over time-scales of days to years, depending on the disc’s accretion rate, viscosity, and SMBH’s mass. We also examine the effect of fallback material on the warp evolution of TDE discs, and find that the fallback torque aligns the TDE disc with the SMBH’s equatorial plane in a few to tens of days for the parameter space investigated. Our results place constraints on models of TDE emission which rely on the changing disc orientation with respect to the line of sight to explain observations.

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