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Dynamo Activity in Strongly Magnetized Accretion Disks

Event Details

Event Dates: 

Friday, January 29, 2016 - 12:00pm

Seminar Location: 

  • JILA 10th Floor - Foothills Room

Speaker Name(s): 

Greg Salvesen

Speaker Affiliation(s): 

CU Boulder
Seminar Type/Subject

Scientific Seminar Type: 

  • Astrophysics Lunch Seminar

Event Details & Abstract: 

The compelling observational evidence for strongly magnetized accretion disks around black holes and their attractive theoretical properties warrant an investigation into how such a disk magnetization state can develop and persist.  The structure and evolution of these disks are governed by a dynamo-like mechanism, which channels part of the accretion power liberated by the magnetorotational instability (MRI) into an ordered toroidal magnetic field.  To study this dynamo activity, we performed a suite of accretion disk simulations in the local limit ( i.e., shearing boxes).  We find that the entire disk develops into a magnetic pressure-dominated state for a sufficiently strong net vertical magnetic flux and dynamo activity persists.  Still stronger fields result in a highly inhomogeneous disk structure, with large density fluctuations. Finally, we show that the magnetized state of the disk in our simulations is well-matched by an analytic model describing the creation and buoyant escape of toroidal field.