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SUMMARY:Celestial fluid mechanics: the nonlinear gas dynamics of discs aro
 und stars and black holes - Gordon Ogilvie\, DAMTP
DTSTART:20240126T160000Z
DTEND:20240126T170000Z
UID:TALK210268@talks.cam.ac.uk
CONTACT:Professor Grae Worster
DESCRIPTION:Thin discs of gas in orbital motion around a massive central b
 ody\, such as a star or black hole\, are found throughout the Universe. Th
 ey include the discs of dusty gas around young stars\, in which planetary 
 systems are born\, and high-energy plasma accretion discs around black hol
 es\, both in the centres of galaxies and around stellar remnants within ou
 r own Galaxy.\n\nAstrophysical discs are (Rayleigh-stable) rotating shear 
 flows of extremely high Reynolds number and support a variety of oscillati
 ons\, waves and instabilities. Fluid-mechanical processes (which may also 
 involve magnetic fields or solid particles\, not discussed in this talk) g
 overn not only the evolution of discs\, by regulating the transport of ang
 ular momentum\, but also the structures that are increasingly observed wit
 hin them\, including rings\, arcs\, spirals and warps.\n\nThis talk explor
 es a variety of problems of nonlinear gas dynamics in discs in which a non
 -circular or non-planar orbital geometry drives oscillatory flows within t
 he disc. I will survey a range of physical models\, as well as asymptotic 
 and variational methods\, that can capture the relevant degrees of freedom
  and the (often resonant) couplings between them\, as seen in numerical si
 mulations. A recurring feature is that internal waves can be destabilized 
 by the oscillatory flows.\n\nIf time allows\, I will also introduce a nove
 l approach to gravitational instability in discs (a mechanism capable of f
 orming either bound objects or long-lived spiral structure)\, in which the
  nonlinear gas dynamics gives rise to subcritical behaviour that may help 
 to explain a self-sustaining process for gravitational turbulence.\n
LOCATION:MR2
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