Reverse stellar evolution, quasars and low-mass X-ray binaries

Recently, Mathews has proposed¹ a mechanism for the mass supply to a black hole in the centre of a quasar (see also ref. 2). According to this proposal the X rays from the central source penetrate the photosphere surrounding low-mass stars. The absorbed energy is distributed over the stellar interior by convection, and the star expands rapidly. Its outer layers are then stripped by the radiation field of the central source. There are two major uncertainties in this model of reversed evolution; the depth to which the X rays impinging on a low-mass star can penetrate before they are absorbed and the inward transport of the energy flux. The crucial hypothesis of Mathews is that the X rays are absorbed within the convection zone. We now test this hypothesis by considering the effects of X-ray absorption in the secondaries of low-mass X-ray binaries. We conclude that reverse evolution does not occur.