Black Shells on Edge of Collapse

Abstract

AdS black bubbles or black shells, first proposed by Danielsson, Dibitetto, and Giri in 2017, are quantum-gravity inspired ultra-compact objects which provide an alternative to black holes. While retaining the thermodynamical properties of black holes to a distant observer, they lack an event horizon and thus evade the formidable challenges associated with black holes such as the information paradox. In 2021, Danielsson and collaborators conducted the first fully non-linear study of the stability of the black shells against radial perturbations and accretion of matter. They concluded that black shells could be kept in equilibrium by a two-parameter internal flux model. In the same year, Danielsson and Giri extended the stability analysis to slowly-rotating shells and derived the flux parameter values necessary for linear stability and slow rotation. In this thesis, I revisit the stability results derived in these papers. I carry out the fully non-linear, time-domain simulations of the non-rotating spherical shell at the flux values that linear theory singled out as necessary and marginally stable for a slowly-rotating shell. My results show that any finite perturbation—no matter how small—drives these marginal configurations to rapid collapse, forming a Schwarzschild horizon within a few hundred light-crossing times. Moreover, neighboring flux pairs that were deemed acceptable by the linear criteria also fail once non-linear mode coupling is taken into account. These findings overturn the provisional stability claimed for rotating black shells, and suggest that additional dissipative channels or fundamentally different flux dynamics would be required for such horizon-less objects to survive in realistic astrophysical environments. Furthermore, using Fourier Neural Operators, I re-examine the relative importance of the flux and viscosity parameters to the stability of the shells. The results indicate that earlier studies have greatly underestimated the role played by the viscosity parameter.