Research Accomplished

A first-order correction in the $\alpha$-viscosity parameter of Shakura & Sunyaev has been introduced in the inviscid and thin accretion disc. A linearised time-dependent perturbative study of the stationary solutions of this quasi-viscous disc, reveals the development of a secular instability on large spatial scales. This qualitative feature is equally manifest for two different types of perturbative treatment - a standing wave on subsonic scales, as well as a radially propagating wave. Stability of the flow is restored when viscosity disappears.