Time: 10:00-11:00, Thursday, September 24 2026
Venue: E14-212
Speaker: Ioannis Soranidis
Title: Regular Ultracompact Objects: From Quantum-Gravitational Cores to Stability and Thermodynamics
Abstract: Regular ultracompact objects provide a useful arena for exploring how classical black-hole geometries may be modified at high curvature while retaining a well-controlled exterior spacetime. In this talk, I will discuss different aspects of their construction and phenomenology, with particular emphasis on regular geometries arising from effective loop-quantum-gravity-inspired dynamics. I will first review how regular black holes and their horizonless counterparts can be supported, and contrast matter-sourced constructions with effective vacuum geometries in which regularization is encoded directly in the gravitational dynamics. Within a deparameterized, spherically symmetric framework, the latter admit a Birkhoff-type property and can be characterized by de Sitter or anti-de Sitter cores, as well as by more specialized horizon structures such as degenerate inner horizons. I will then discuss some of their characteristic geometric properties and the role played by a fundamental minimal length scale. Particular attention will be given to the stability of the inner horizon and the mass-inflation problem, including whether inner-extremal configurations can ameliorate the usual instability. Finally, I will turn to black-hole thermodynamics in asymptotically anti-de Sitter spacetime. I will show how the regular core modifies the physical horizon branch and the Hawking–Page transition, and how different core geometries can lead to quantitatively distinct phase structures. Together, these results illustrate how the mechanism responsible for regularization can leave observable imprints on both the dynamical and thermodynamic properties of ultracompact objects.
