Alternatives to Black Holes: Gravastars and Plugstars

Abstract

The images collected by the EHT of objects M87* and SgrA* show darkened, but not black areas. So that the immediate identification with supermassive black holes remains questionable. Attention is thus focused on the main alternative candidates: gravastars, which have attracted a great deal of attention for decades. However, none of these models provides any evidence that can successfully confront these observational data. We present an interpretation derived directly from Schwarzschild’s inner geometry, in the subcritical case where the intense pressure gradient counterbalances the force of gravity. The object then exhibits a gravitational redshift effect leading to a wavelength ratio of 3, which is remarkably consistent with image analysis. A mechanism is proposed to ensure the self-stability of such objects, which are then referred to as plugstars.