Burst occurrence in young massive stellar objects

Abstract

Episodic accretion-driven outbursts are an extreme manifestation of accretion variability. It has been proposed that the development of gravitational instabilities in the proto-circumstellar medium of massive young stellar objects (MYSOs) can lead to such luminous bursts, when clumps of fragmented accretion discs migrate on to the star. We simulate the early evolution of MYSOs formed by the gravitational collapse of rotating 100-M pre-stellar cores and analyse the characteristics of the bursts that accompany their strongly time-variable protostellar light curve episodically. We predict that MYSOs spend ≈103 yr (≈1.7 per cent) of their modelled early 60 kyr experiencing eruptive phases, during which the peak luminosity exceeds the quiescent pre-burst values by factors from 2.5 to more than 40. Throughout these short time periods, they can acquire a substantial fraction (up to ≈50 per cent) of their zero-age main-sequence mass. Our findings show that fainter bursts are more common than brighter ones. We discuss our results in the context of the known bursting MYSOs, e.g. NGC 6334I-MM1 and S255IR-NIRS3, and propose that these monitored bursts are part of a long-time ongoing series of eruptions, which might, in the future, be followed by other luminous flares.