Accreting Schwarzschild-like compact object: Plasma-photon interaction and stability

Abstract: Accretion is a common phenomenon associated with any astrophysical compact object, which is best described by plasma, a state of matter composed of electrons and heavy ions. In this paper, we analyze the linear dynamics of electromagnetic (EM) fields propagating through the accreting plasma around a static and spherically symmetric horizon-less, exotic compact object (ECO). The general equations governing the propagation of EM waves in such a background exhibits quasi-bound states, with a characteristic oscillation around the BH values, for both the axial and the polar modes, as well as for homogeneous and inhomogeneous plasma distributions. The amplitude of these oscillations depend on the non-zero reflectivity of the surface of the compact object, while the oscillation length depends on its compactness. This results into slower decay of the quasi-bound states with time for certain parameter space of the plasma frequency, compared to BHs, making these ECOs more prone to instabilities.