Research Fellows Directory
Professor Steven Balbus Savilian Professor of Astronomy
University of Oxford
I work in the area of astrophysical fluid dynamics. This transcends several different disciplines because the underlying principles of fluid motion are a feature shared by many different systems. The bulk of my effort in the last few years has been devoted to understanding how accretion discs behave around black holes behave. Magnetism is an essential feature in these discs. Magnetic forces, even weak forces, entrained in the swirling material, profoundly destabilise the rotation of the gaseous fluid, rendering the flow turbulent. Following the development of this turbulent flow is very difficult and requires using powerful computers. The study of turbulence is notoriously difficult subject and is poorly understood even when no magnetic fields are involved (like water in a pipe); matters are yet more complex with a magnetism. A sort of internal friction known as viscosity is present in all gases, and this friction causes the turbulent motions to heat the gas. Magnetised turbulence is also heated by ohmic resistance, not unlike a wire! How viscosity and resistance act together turns out to be an important question that is relevant to they way that black hole accretion discs
behave, even on gross macroscopic scales. We need to understand these kinds of processes if we are to understand how black holes form and evolve.
I also work on rotation inside stars, trying to understand how the sun and other stars achieve the peculiar patterns of rotation we can "observe" via techniques that are similar to seismology. "Star quakes" make the light flicker, and by carefully analysing this flicker, we can understand what the interior of the star is doing.
Finally, I also work on more classical problems, like tides from the sun and moon. They may have changed over time due to plate tectonics and an evolving lunar orbit. Were tides an important factor for the emergence of vertebrates from the sea? This may now be
Interests and expertise (Subject groups)