Date:
Tue, 15/09/200912:15-13:15
Location:
Kaplun Bldg, seminar room, 2nd floor
Anomalous resistivity enables disk formation in magnetized cloud
cores
Accretion disks are needed by most jet launching mechanisms. However, disk formation in star-forming cloud cores is hindered by excessive magnetic braking. Previous work indicates that braking torques can suppress the formation of rotationally supported disks, both in the ideal MHD limit and in the presence of ambipolar diffusion (for the expected magnetization levels and typical rates of cosmic ray ionization).
Our recent simulations show that Ohmic dissipation can in principle enable disk formation. We follow for 30,000 years the collapse of a rotating, magnetized envelope onto a central mass, using a range of values of resistivity. For the smaller resistivities in the range, magnetic braking still prevents disk formation. A Keplerian disk appears for eta of the order of 10^19 cm^2/s, an anomalous resistivity much larger than the classical microscopic value. We explore the dependence of this resistivity value on core magnetization.
cores
Accretion disks are needed by most jet launching mechanisms. However, disk formation in star-forming cloud cores is hindered by excessive magnetic braking. Previous work indicates that braking torques can suppress the formation of rotationally supported disks, both in the ideal MHD limit and in the presence of ambipolar diffusion (for the expected magnetization levels and typical rates of cosmic ray ionization).
Our recent simulations show that Ohmic dissipation can in principle enable disk formation. We follow for 30,000 years the collapse of a rotating, magnetized envelope onto a central mass, using a range of values of resistivity. For the smaller resistivities in the range, magnetic braking still prevents disk formation. A Keplerian disk appears for eta of the order of 10^19 cm^2/s, an anomalous resistivity much larger than the classical microscopic value. We explore the dependence of this resistivity value on core magnetization.