Beyond black holes: universal properties of ‘ultra-massive’ spacetimes

Abstract

It has been long known that in spacetimes with a positive cosmological constant the area of spatially stable marginally trapped surfaces (MTSs) has a finite upper bound given by . In this paper I show that any such spacetime containing spatially stable MTSs with area approaching indefinitely that bound acquire universal properties generically. Specifically, they all possess generalized ‘holographic screens’ (i.e. marginally trapped tubes) foliated by MTSs of spherical topology, composed of a dynamical horizon portion and a timelike membrane portion that meet at a distinguished round sphere with constant Gaussian curvature —and thus of maximal area . All future (past) generalized holographic screens (GHSs) containing change signature at , and all of them continue towards the past (future) with non-decreasing (non-increasing) area of their MTSs. A future (past) singularity arises. For the future case, these ‘ultra-massive spacetimes’ Senovilla (2023 Port. Math. 80 133–55) may be more powerful than black holes (BHs), as they can overcome the repulsive Λ-force and render the spacetime as a collapsing Universe without event horizon enclosing those GHSs. It is remarkable that these behaviours do not arise if Λ is non-positive. The results have radical implications on BH mergers and on very compact objects accreting mass from their surroundings—if .