Viscous damping of r-modes: Small amplitude instability

Understand

We study the viscous damping of r-modes of compact stars and analyze in detail the regions where small amplitude modes are unstable to the emission of gravitational radiation.

• We present general expressions for the viscous damping times for arbitrary forms of interacting dense matter and derive general semi-analytic results for the boundary of the instability region.
• These results show that many aspects, like in particular the physically important minima of the instability boundary, are surprisingly insensitive to detailed microscopic properties of the considered form of matter.
• Our general expressions are applied to the cases of hadronic stars, strange stars, and hybrid stars, and we focus on equations of state that are compatible with the recent measurement of a heavy compact star.