The Viscous Evolution of Elliptical Accretion Discs

Abstract

We examine critically the widely accepted assumption that an accretion flow should circularise on a timescale much shorter than its viscous inflow timescale. We use both first order perturbation analysis and a numerical (sticky particle) method to investigate the viscous evolution of a disc consisting of a series of nested elliptical streamlines. The analytical results indicate that, to first order, elliptical discs evolve under the action of viscous stresses so as to preserve their ellipticity. The numerical results also indicate that initially eccentric discs should remain so over a viscous timescale