BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Global simulations of self-gravitating magnetized protoplanetary d
 isks - Dr. Hongping Deng (DAMTP\, Cambridge)
DTSTART:20200225T130000Z
DTEND:20200225T140000Z
UID:TALK133573@talks.cam.ac.uk
CONTACT:Chris Hamilton
DESCRIPTION:In the early stages of a protoplanetary disk\, when its mass i
 s a significant fraction of its star's\, turbulence generated by gravitati
 onal instability (GI) should feature significantly in the disk's evolution
 . At the same time\, the disk may be sufficiently ionised for magnetic fie
 lds to play some role in the dynamics. Though usually neglected\, the impa
 ct of magnetism on the GI may be critical\, with consequences for several 
 processes: the efficiency of accretion\, spiral structure formation\, frag
 mentation\, and the dynamics of solids. In this paper\, we report on globa
 l three-dimensional magnetohydrodynamical simulations of a self-gravitatin
 g protoplanetary disk using the meshless finite mass (MFM) Lagrangian tech
 nique. We confirm that GI spiral waves trigger a dynamo that amplifies an 
 initial magnetic field to nearly thermal amplitudes (plasma β < 10)\, an 
 order of magnitude greater than that generated by the magneto- rotational 
 instability alone. We also determine the dynamo's nonlinear back reaction 
 on the gravitoturbulent flow: the saturated state is substantially hotter\
 , with an associated larger Toomre parameter and weaker\, more 'flocculent
 ' spirals. But perhaps of greater importance is the dynamo's boosting of a
 ccretion via a significant Maxwell stress\; mass accretion is enhanced by 
 factors of several relative to either pure GI or pure MRI. Our simulations
  use ideal MHD\, an admittedly poor approximation in protoplanetary disks\
 , and thus future studies should explore the full gamut of non-ideal MHD. 
 In preparation for that\, we exhibit a small number of Ohmic runs that rev
 eal that the dynamo\, if anything\, is stronger in a non-ideal environment
 . This work confirms that magnetic fields are a potentially critical ingre
 dient in gravitoturbulent young disks\, possibly controlling their evoluti
 on\, especially via their enhancement of (potentially episodic) accretion.
  
LOCATION:MR21\, Centre for Mathematical Sciences\, Wilberforce Road\, Camb
 ridge
END:VEVENT
END:VCALENDAR