Magnetorotational instability

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Magnetorotational instability

• More about viscous disks
• The magnetorotational instability
• Basic physics
• Computer simulations
• Laboratory experiments

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Computer simulations of the MRI
Pseudo-Newtonian simulation use a modified
Newtonian potential to approx. effects of
GR Hawley Krolik (2001)
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Density
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Full GR-MHD calculations (Hirose et al. 2004)
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Findings

• Accretion disks are always driven into a
  turbulent state by the MRI
• Turbulence transports angular momentum and allows
  accretion to proceed
• For most of disk, end result is crudely in
  agreement with the alpha-prescription
• Variability of turbulence explains why accreting
  sources are variable sources of radiation
• Magnetic fields have interesting effects close to
  the innermost stable circular orbit (ISCO)
• Magnetic fields connect plunging material within
  the ISCO to the disk outside
• Can continue to extract energy and angular
  momentum from matter even inside of the ISCO

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How do we know this is true?

• To date, most of this work on the physics of
  accretion disks is theoretical
• We argue from basic physical principals that
  disks must behave like this
• Little direct observational evidence for the MRI
  in real accretion disks
• There is some interesting laboratory work

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Prof. Lathrops Laboratory in UMd-Physics
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