Accretion bursts in high-mass young stellar objects

In the past few years, accretion bursts in young stellar objects (YSOs) have gained increasing relevance in star formation. The latest picture of YSO evolution suggests that a large portion (up to 30-40%) of their final mass might be gathered during accretion bursts. Indeed, most recent observations have corroborated the idea that episodic accretion is a universal phenomenon across mass and time in star formation. The study of episodic accretion in high-mass young stellar objects (HMYSOs) is still in its infancy. In the past six years, we have been detecting four bona-fide bursts from HMYSOs (S255IR NIRS3, NGC 6334I-MM1, G358.93-0.03 MM1, G323.46-0.08), two (M17 MIR, V723 Car) from possible HMYSOs in the making, and two periodic HMYSOs outbursters (G24.33+0.14, G107.30+5.64).
Despite the small sample of outbursters, a large variety of physical properties (in terms of accreted mass, released energy and length of the burst) has been observed, similarly to their low-mass counterparts. However, released energy, mass accretion rates and accreted mass of such episodes are orders of magnitude larger than in low-mass young stars.
In addition to “classical” direct methods for detecting bursts, such as multi-wavelength light-curves and multi-epoch spectroscopy, other indirect tracers, like CH₃OH and H₂O maser flares or radio jet bursts, can be used for revealing and studying episodic accretion in HMYSOs.