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Like their lower mass siblings, massive protostars can be expected to: a) besurrounded by circumstellar disks and b) launch magnetically-driven jets andoutflows. The disk formation and global evolution is thereby controlled byadvection of angular momentum from large scales, the efficiency of magneticbraking and the resistivity of the medium, and the internal thermal andmagnetic pressures of the disk. We perform a series of 30 simulations of amassive star forming from the gravitational collapse of a molecular cloudthreaded by an initially-uniform magnetic field, starting from different valuesfor the mass of the cloud, its initial density and rotation profiles, itsrotational energy content, the magnetic field strength, and the resistivity ofthe material. The gas and dust is modeled with the methods of resistivemagnetohydrodynamics, also considering radiation transport of thermal emissionand self-gravity. After the initial infall phase dominated by the gravitationalcollapse, an accretion disk is formed, shortly followed by the launching ofmagnetically-driven outflows. Two layers can be distinguished in the accretiondisk: a thin layer, vertically supported by thermal pressure, and a thicklayer, vertically supported by magnetic pressure. We observe the effects ofmagnetic braking in the inner ~50 au of the disk at late times in our fiducialcase. The parameter study reveals that the size of the disk is mostlydetermined by the density and rotation profiles of the initial mass reservoirand not by the magnetic field strength. Magnetic pressure can slightly increasethe size of the accretion disk, while magnetic braking is more relevant in theinnermost parts of the disk as opposed to the outer disk. From the parameterstudy, we infer that multiple initial conditions for the onset of gravitationalcollapse are able to produce a given disk size and protostellar mass.

Modeling disks and magnetic outflows around a forming massive star: I. Investigating the two layer-structure of the accretion disk