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Whether protoplanetary disks accrete at observationally significant rates by the magnetorotational instability (MRI) depends on how well ionized they are. Disk surface layers ionized by stellar X-rays are susceptible to charge…
The temperature in most parts of a protoplanetary disk is determined by irradiation from the central star. Numerical experiments of Watanabe \& Lin (2008) suggested that such disks, also called `passive disks', suffer from a thermal…
AIM:The aim of this work is to understand to what extend gravitational interactions between the stars in high-density young stellar clusters, like the Orion Nebula Cluster (ONC), change the angular momentum in their protoplanetary discs.…
We report results from calculations investigating stationary magnetic field configurations in accretion discs around magnetised neutron stars. Our strategy is to start with a very simple model and then progressively improve it providing…
We demonstrate with a nonlinear MHD code that angular momentum can be transported due to the magnetic instability of toroidal fields under the influence of differential rotation, and that the resulting effective viscosity may be high enough…
Discs of gas and dust are ubiquitous around protostars. Hypothetical disc viscosity is thought to cause the gas and dust to accrete onto the star. Turbulence within the disc might be the source of this disc viscosity. However, observed…
We propose that the strength of angular momentum transport in accretion discs threaded by net vertical magnetic field is determined by a self-regulation mechanism: the magnetorotational instability (MRI) grows until its own turbulent…
The magnetorotational instability (MRI) of a weakly ionized, differentially rotating, magnetized plasma disk is investigated in the multi-fluid framework. The disk is threaded by a uniform vertical magnetic field and charge is carried by…
Young stars and planetary systems form in molecular clouds. For classical T Tauri stars (CTTS, F-K type precursors) the accretion disk does not reach down to the central star, but it is truncated near the co-rotation radius. The inner edge…
We use three-dimensional magnetohydrodynamical (MHD) simulations to study the formation of a corona above an initially weakly magnetized, isothermal accretion disk. We also describe a modification to time-explicit numerical algorithms for…
We examine heating and cooling in protostellar disks using 3-D radiation-MHD calculations of a patch of the Solar nebula at 1 AU, employing the shearing-box and flux-limited radiation diffusion approximations. The disk atmosphere is ionized…
The tidal interaction between a disk and a planet leads to the planet's migration. A long-standing question regarding this mechanism is how to stop the migration before planets plunge into their central stars. In this paper, we propose a…
We discuss recent progress in understanding the launching of outflows/jets from the disc-magnetosphere boundary of slowly and rapidly rotating magnetized stars. In most of the discussed models the interior of the disc is assumed to have a…
We present a linear analysis of the vertical structure and growth of the magnetorotational instability in stratified, weakly ionised accretion discs, such as protostellar and quiescent dwarf novae systems. The method includes the effects of…
We present results from radiation non-ideal magnetohydrodynamics (MHD) calculations that follow the collapse of rotating, magnetised, molecular cloud cores to stellar densities. These are the first such calculations to include all three…
Mean-motion resonances (MMRs) form through convergent disc migration of planet pairs, which may be disrupted by dynamical instabilities after protoplanetary disc (PPD) dispersal. This scenario is supported by recent analysis of TESS data…
The nearest accretion disc to us in space if not time was the protosolar nebula. Remnants of this nebula thus potentially offer unique insight into how discs work. In particular the existence of chondrules, which must have formed in the…
The origin of large-scale and coherent magnetic fields in astrophysical discs is an important and long standing problem. Researchers commonly appeal to a turbulent dynamo, sustained by the magneto-rotational instability (MRI), to supply the…
MHD turbulence plays a crucial role in the dust dynamics of protoplanetary discs. It affects planet formation, vertical settling and is one possible origin of the large scale axisymmetric structures, such as rings, recently imaged by ALMA…
Whether the angular momentum of protoplanetary discs is redistributed by viscosity or extracted by magnetised winds is a long-standing question. Demographic indicators, such as gas disc sizes and stellar accretion rates, have been proposed…