Akademik Veri Yönetim Sistemi
CLASSICAL AND QUANTUM GRAVITY, cilt.40, sa.18, ss.1-24, 2023 (Hakemli Dergi)
With the recent progress in observations of astrophysical black holes,
it has become more important to understand in detail the physics of
strongly gravitating horizonless objects. If the objects identified in
the observations are indeed horizonless and ultracompact, high curvature
effects may become important, and their explorations may be intimately
related to new physics beyond General Relativity (GR). In this paper, we
revisit the concept of statistical thermodynamics in curved spacetime,
focusing on self-gravitating compact systems without event horizons. In
the literature, gravitational field equations are in general assumed a priori
in the thermodynamic treatment, which may lead to difficulties for
theories of modified gravity, given the more complicated structure of
field equations. Here, we consider thermodynamic behavior of the matter
source, instead of the physical mass, hence avoiding the explicit input
of field equations in the derivation of thermodynamic laws. We show that
the conventional first law of thermodynamics is retrieved once the thermodynamic volume,
which is in general different from the geometric volume, is
appropriately identified. For demonstrations of our approach, we
consider familiar examples of self-gravitating gas in GR, where the
connection to previous studies becomes clear. We also discuss 2-2-holes
in quadratic gravity, a novel example of black hole mimickers that
features super-Planckian curvatures in the interior. These objects
exhibit universal high curvature effects in thermodynamics, which happen
to be conveniently encoded in the thermodynamic volume. Interesting
connections to black hole thermodynamics also emerge when the physical
mass is treated as the total internal energy.