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Thermodynamics of self-gravitating fermions as a robust theory for dark matter halos: Stability analysis applied to the Milky Way

A. Krut

C. R. Argüelles

P.-H. Chavanis

  • ICRANet, Piazza della Repubblica 10, I-65122 Pescara, Italy

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Phys. Rev. D 113, 023010 – Published 7 January, 2026

DOI: https://doi.org/10.1103/346d-d17c

Abstract

We present a framework for dark matter halo formation based on a kinetic theory of self-gravitating fermions together with a solid connection to thermodynamics. Based on maximum entropy arguments, this approach predicts a most likely phase-space distribution which takes into account the Pauli exclusion principle, relativistic effects, and particle evaporation. The most general equilibrium configurations depend on the particle mass and develop a degenerate compact core embedded in a diluted halo, both linked by their fermionic nature. By applying such a theory to the Milky Way we analyze the stability of different families of equilibrium solutions with implications on the dark matter distribution and the mass of the dark matter particle candidate. We find that stable core-halo profiles, which explain the dark matter distribution in the Galaxy, exist only in the range mc2≈194–387  keV. The lower bound is a consequence of imposing thermodynamical stability on the core–halo solutions having a 4.2×106M⊙ quantum core mass alternative to the black hole hypothesis at the Galaxy center. The upper bound is solely an outcome of general relativity when the quantum core reaches the Oppenheimer-Volkoff limit and undergoes gravitational collapse toward a black hole. We demonstrate that stable core-halo profiles exist which are astrophysically relevant in the sense that their total mass is finite, do not suffer from the gravothermal catastrophe, and agree with observations. The morphology of the halo tail is described by a polytrope of index 52, developing a sharp decline of the density beyond 25 kpc in excellent agreement with the latest Gaia DR3 rotation curve data. Moreover, we obtain a total Milky Way mass of about 2×1011M⊙ including baryons and a local dark matter density of about 0.4  GeV c−2 cm−3 in line with recent independent estimates.

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Phys. Rev. D 113, 023010– Published 7 January, 2026
  • Received 13 March 2025
  • Accepted 1 December 2025
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