It has recently become evident from both numerical studies and observations
that accretion onto young protostars may have a highly variable
character with episodic bursts revealing themselves as FU-Orionis-type and
EX-Lupi-like eruptions. This newly emerging paradigm is beginning to
supersede the classical Shu-Larson-Penston steady accretion model and this
may have important consequences for the evolution of stars and planets. I
will review the current status of the variable accretion paradigm,
focusing on the disk gravitational instability and fragmentation model, in
which accretion bursts are triggered by fragments migrating onto the star.
Various implications of variable accretion
on both young stars and their protostellar disks will be discussed.
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