Journal of Fluid Mechanics Webinar Series: Steven Balbus, University of Oxford, UK

The Leeds Institute for Fluid Dynamics is delighted to partner with the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge, the UK Fluids Network, and the Journal of Fluid Mechanics to deliver a regular webinar series on fluids-related topics.

The autumn edition of the Fluid Mechanics Webinar Series will take place over ten weeks between 2nd October and 4th December 2020. Registration will remain open, and please note that if you have already registered you need not register again.

Video recordings of past webinars will be made available soon. Watch this space!

Speaker: Steven Balbus, University of Oxford, UK

Date/Time: Friday 13th November, 2020. 4:00 pm GMT/11 am EST

Title: Time-dependent accretion discs around Kerr black holes and tidal disruption events

Abstract: The theory of Newtonian astrophysical accretion discs, both in its steady and time-dependent form, dates from the mid-1970s. Relativistic thin disc theory was developed at nearly the same time, but only for steady-state conditions. I will present recent work on the fluid dynamics of time-dependent accretion discs around Kerr black holes. This work has a natural application to so-called tidal disruption events (TDEs), the tidal break-up of star when it passes too close to a galaxy's central black hole. The stellar debris collects into a disc, whose inner boundary corresponds to a radius at which the Rayleigh criterion for rotational stability is violated according to general relativity. This requires some care in its treatment, particularly with regard to the inner stress, since both the interpretation of astronomical observations and numerical simulations depend upon a detailed understanding of this innermost stable circular orbit. TDEs generally exhibit a slowly decreasing light curve that is not at present well-understood. It is, however, quite consistent with an extended evolutionary phase of time-dependent relativistic disc theory. The interplay between mathematics, fluid theory, and astrophysics is particularly striking for these objects.