Nomen non est omen: Why it is too soon to identify ultra-compact objects as black holes

Abstract

Black holes play a pivotal role in the foundations of physics, but there is an alarming discrepancy between what is considered to be a black hole in observational astronomy and theoretical studies. Despite claims to the contrary, we argue that identifying the observed astrophysical black hole candidates as genuine black holes is not justified based on the currently available observational data, and elaborate on the necessary evidence required to support such a remarkable claim. In addition, we investigate whether the predictions of semiclassical gravity are equally compatible with competing theoretical models, and find that semiclassical arguments favor horizonless configurations.

5 pages, 1 figure. Published version. Selected Honorable Mention in the 2023 Gravity Research Foundation Essay Competition. Comments welcome!

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Cited by in corpus (9)

• Regular black holes and the first law of black hole mechanics
• Light rings and causality for nonsingular ultracompact objects sourced by nonlinear electrodynamics
• Kinematic and energy properties of dynamical regular black holes
• Models of cosmological black holes
• Euclidean methods and phase transitions for the strongest deformations compatible with Schwarzschild asymptotics
• Horizon-bound objects: Kerr--Vaidya solutions
• Exotic Encounters: Buchdahl's Conditions and Physical Black Holes
• Internal structure of Hayward black holes
• Apparent horizon as a membrane