Sub-stellar Strange Quark Matter Objects: Predicting a New Class of Highly-Compact Candidates

Abstract

We investigate the existence and stability of highly-compact sub-stellar objects composed of strange quark matter (SQM), focusing on finite-size strangelets with baryon number $A \leq 100$. Motivated by the emergence of mass--radius outliers in the \textit{Gaia} DR3 era, we employ a Bayesian exploration of the MIT bag-model parameter space, explicitly accounting for finite-size surface and curvature contributions that become relevant at low baryon number. Enforcing the bulk absolute-stability requirement for SQM ($E/A < 930~\mathrm{MeV}$), we find that self-gravitating equilibrium sequences are confined to the sub-stellar regime, with typical masses $M \simeq 10^{-2}$--$10^{-1}\,M_{\odot}$ and characteristic radii of order $10^{3}$--$10^{4}$ km. We further show that rapid rotation, treated through a self-consistent framework that incorporates relativistic thermodynamics, can substantially inflate the equatorial radius and extend the accessible mass--radius domain. While rotation does not eliminate the intrinsic high-density compactness of these configurations, it shifts the most extended models closer to the observational parameter space of massive exoplanets. A comparison with objects from the NASA Exoplanet Archive reveals a pronounced density gap separating standard atomic-matter planets and brown dwarfs from the strangelet-rich branch predicted here. We conclude that light strangelets cannot account for solar-mass white dwarfs, but they robustly predict a previously unexplored population of ultra-compact sub-stellar objects, offering testable targets for future microlensing searches and high-cadence photometric surveys.