Debanjan Debnath, Rikpratik Sengupta, Kaushik Bhattacharya

We present a class of horizonless, regular ultra-compact objects arising in a theory of gravity which allows curvature-fluid coupling. The non-minimal interaction between fluid variables and the Ricci scalar generates a vacuum-like equation of state in the interior, while the exterior remains exactly Schwarzschild. The two spacetimes are glued through a shell at the junction. The interior metric is non-singular, the shell acquires a stiff-matter equation of state, and near-horizon compactness can potentially mimic black-hole phenomenology without event horizons. Unlike the Mazur-Mottola gravastar and its variants, the present model naturally selects a typical ultra-compact mass-radius window, with masses in the range $1.4$-$2.1 M_\odot$ and radii in the range 5-7 km. This framework predicts a unique geometric-thermodynamic shell temperature in the ultra-compact limit distinctly different from the Hawking expression and the other unique observational feature of the model is the prediction of mass independent luminosity.