For distant observers stationary black holes are objects existing in the infinite future. This stems from asymptotic behaviour of inbound null geodesics at their critical radii. However, these objects either exist in a vacuum or are the source of an electromagnetic field if charged. By contrast, astrophysical black holes emit radiation [1] and exist in an environment containing accreting matter. More realistic models of black holes due to Vaidya [2] exchange mass-energy with their environment and consequently these solutions are non-stationary. Recently the Vaidya metric was presented in diagonal form [3], and this exposes features that may not be apparent in the traditional Eddington-Finkelstein form. One of these features appears to be an abrupt change in the direction of gravitational acceleration close to the critical radius, leading to a diverging potential barrier halting further collapse. It must be noted however, that this may only be a feature of the specific solution considered here, and such behaviour may not be generic. The purpose of this letter is to show how this comes about, and to suggest that, if true generally, would imply a resolution of the information paradox. 1. Hawking SW. Black hole explosions. Nature, 248 30 (1974). 2. Vaidya P. The Gravitational Field of a Radiating Star. Proceedings of the Indian Academy of Sciences, A33 264 (1951). 3. Berezin VA, Dokuchaev VI and Eroshenko Yu N. Vaidya Spacetime in the Diagonal Coordinates. Journal of Experimental and Theoretical Physics, 124(3) 446 (2017).