The backreaction of stellar wobbling on accretion discs of massive protostars

Abstract

black In recent years, it has been demonstrated that massive stars see their infant circumstellar medium shaped into a large irradiated, gravitationally unstable accretion disc during their early formation phase. Such discs constitute the gas reservoir from which nascent high-mass stars gain a substantial fraction of their mass by episodic accretion of dense gaseous circumstellar clumps, simultaneously undergoing accretion-driven bursts and producing close-orbit spectroscopic companions of the young high-mass stellar object. We aim to evaluate the effects of stellar motion caused by the disc non-axisymmetric gravitational field on the disc evolution and its spatial morphology. In particular, we analyse the disc's propensity to gravitational instability and fragmentation and the disc's appearance in synthetic millimetre band images pertinent to the ALMA facility. We employed three-dimensional radiation-hydrodynamical simulations of the surroundings of a young massive star in the non-inertial spherical coordinate system, adopting the highest spatial resolution to date and including the indirect star-disc gravitational potential caused by the asymmetries in the circumstellar disc. The resulting disc configurations were post-processed with the radiation transfer tool RADMC-3D and CASA software to obtain synthetic images of the disc. We confirm that the early evolution of the accretion disc is notably different when stellar wobbling is taken into account. The redistribution of angular momentum in the system makes the disc smaller and rounder, reduces the number of circumstellar gaseous clumps formed via disc gravitational fragmentation, and prevents the ejection of gaseous clumps from the disc. The synthetic predictive images at millimetre wavelengths of the accretion disc that includes stellar wobbling are in better agreement with the observations of the surroundings of massive young stellar objects, namely black AFGL 4176 mm1, G17.64+0.16, and G353.273 than our simulations of numerical hydrodynamics that omit this physical mechanism. Our work confirms that stellar wobbling is an essential ingredient to account for in numerical simulations of accretion discs of massive protostars.