Mass accretion to young stars triggered by flaring activity in circumstellar disks | Salvatore Orlando ( INAF- Osservatorio Astronomico di Palermo )

Young low-mass stars are surrounded by circumstellar disks with which they interact in a complex fashion, with accretion of mass and ejection of collimated outflows. The accretion builds up the young star to its final mass and is also believed to power mass outflows, which may in turn remove the excess angular momentum from the star-disk system. However, although the process of mass accretion is a critical aspect of star formation, its mechanisms are still to be fully understood. A point not considered to date and important for the accretion process is the evidence of very energetic and frequent flaring events in these stars. Flares may easily perturb the stability of the disks, thus influencing the transport of massand angular momentum. Here we report three-dimensional magnetohydrodynamic modeling of the evolution of a flare occurring on the disk around a rotating magnetized star, which reveals that the resulting perturbation of the disk triggers a significant mass accretion. This result put forward the frequent flaring activity in young stars as a mechanism that may contribute to stellar mass accretion. This mechanism could be additional to the magnetorotational instability (or even enhance its efficiency), frequently invoked in the literature to explain the transport of mass and angular momentum in the star-disk system.