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Physics Colloquium - Dr Jonathan Squire

Monday, 15 April 2019

Physics Department
Colloquium

Dr Jonathan Squire


Research Fellow

Department of Physics


"Resonant Drag Instabilities and the fluid dynamics of planet formation"


Astrophysical dust is thought to govern a wide variety of processes, from planet and star formation, to winds from massive stars and galaxies. In all such processes, dust and the ambient gas interact through drag and/or Lorentz forces, presenting an interesting problem in fluid dynamics that will be the focus of my talk. Bulk movement between the two phases – for instance, due to thermal pressure gradients or radiation – can drive the fast-growing "Resonant Drag Instability" (RDI), which is unstable whenever the relative dust-gas streaming velocity matches the phase speed of a fluid wave. As it grows nonlinearly, the RDI drives turbulence in the gas, strongly clumping the dust. This physics is of particular interest for the problem of planetesimal formation: how dust coagulates in protoplanetary disks to form self-gravitating planetesimals. In addition to elucidating the physics of the well-studied "streaming instability" – thought to be key for coagulating cm-sized grains – the RDI formalism reveals a number of other related instabilities. Most interestingly, the "settling instability" is a promising mechanism for coagulating smaller grains at lower densities than the streaming instability, providing a possible path for dust to grow from the micron scale up to kilometre-sized bodies where gravity can take over.

WHEN: Monday 15 April 2019
WHERE: Room 314, Science 3 Building
TIME: 3.00 pm–4.00 pm

All interested are welcome to attend

Light refreshments to follow in Common Room