Episodic Accretion Bursts in Protostellar Disks
Shantanu Basu (Univ of Western Ontario) - Oct 9 at 12:00 noon
I report on our recent numerical simulations which have
shown for the first time that recurrent envelope-induced
gravitational instability can lead to a burst mode
of protostellar accretion. The burst mode begins upon
the formation of a centrifugally balanced disk around
a newly formed protostar. It is comprised of prolonged
quiescent periods of low accretion rate (typically less
than 10^{-7} Msun/yr) which are punctuated by intense
bursts of accretion (typically at least 10^{-4} Msun/yr,
with duration ~ 100 yr) during which most of the protostellar
mass is accumulated. The accretion bursts are associated
with the formation of dense protostellar/protoplanetary
embryos, which are later driven onto the protostar by
the gravitational torques that develop in the disk.
Gravitational instability in the disk, driven by continuing
infall from the envelope, is shown to be an effective means of
transporting angular momentum outward, and mass inward to the
protostar. We show that the disk mass always remains significantly
less than the central protostar mass throughout this process.
We conclude that most (if not all) protostars undergo a burst
mode of evolution during their early accretion history,
as inferred empirically from observations of FU Orionis variables.
These results are published in Vorobyov & Basu (2005, ApJ, 633, L137
and 2006, ApJ, 650, 956).
The seminar will be held in 544 Campbell Hall.
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