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| EPoS Contribution |
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The Formation and Early Evolution of Disks
Shantanu Basu Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada | |
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The early phase of disk assembly and evolution,
while traditionally not easily observable, will
become increasingly transparent in the near future.
The early disk phase is actually the most crucial time
for star formation, and can also initiate planet formation. The formation of a disk in the first place depends
on two necessary events: (1) the formation of a small central protostar by direct infall; (2)
a phase of rapid magnetic decoupling, in order to
avoid the 'magnetic braking catastrophe'. Due to magnetic braking, disks are expected to be initially much smaller than inferred from simple estimates of angular momentum conservation. This may be consistent with observations
of some class 0 objects, e.g., IRAM 04191.
However, once formed, disks may quickly achieve a
large enough mass to undergo episodic gravitational
instability, driven by envelope accretion. This is a
viable way to explain the episodic accretion history of YSO's,
and the formation of stellar companions, brown dwarfs, and giant planets on wide orbits. Some intriguing questions: Are magnetic braking and episodic gravitational instability incompatible? Is fine-tuning of theory required to understand observations, and where would that leave the theory? Are the MRI or an ad-hoc alpha viscosity necessary at all to understand star formation, given the significant torques due to gravity and magnetic braking? | |
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Suggested Session:
Early Phases of Disks | |