Accretion bursts in high-mass protostars: A new test bed for models of episodic accretion

Recent observations of high-mass young stellar objects (HMYSOs) with masses \(M_* \gtrsim 10 M_{\odot}\) uncovered outbursts with accretion rates exceeding \(\dot M_*\sim 10^{-3}M_{\odot}~yr^{-1}\). Here, we examine which scenarios proposed in the literature so far to explain accretion bursts of LMYSOs can also apply to the episodic accretion in HMYSOs. We utilise 1D time-dependent models of protoplanetary discs around HMYSOs to study burst properties. We find that discs around HMYSOs are much hotter than those around their low-mass cousins. As a result, a much more extended region of the disc is prone to the thermal hydrogen ionisation and magnetorotational (MRI) activation instabilities. The former, in particular, is found to be ubiquitous in a very wide range of accretion rates and disc viscosity parameters.   The outbursts triggered by these instabilities, however, always have too low of an \(\dot M_*\) and are one to several orders of magnitude too long compared to those observed from HMYSOs to date. On the other hand, bursts generated by tidal disruptions of gaseous giant planets formed by the gravitational instability of the protoplanetary discs yield properties commensurate with observations, provided that the clumps are in the post-collapse configuration  with planet radius \(R_{\rm p} \gtrsim 10\) Jupiter radii.  Furthermore, if observed bursts are caused by disc ionisation instabilities, then they should be periodic phenomena with the duration of the quiescent phase comparable to that of the bursts. This may yield potentially observable burst periodicity signatures in the jets, the outer disc, or the surrounding diffuse material of massive HMYSOs.