https://doi.org/10.1140/epjc/s10052-025-14404-6
Letter
Role of the neutral X-fermion in describing the dark matter of the universe
1
ICRANet, Piazza della Repubblica 10, 65122, Pescara, Italy
2
ICRANet, 1 Avenue Ratti, 06000, Nice, France
3
ICRA, Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185, Rome, Italy
4
INAF, Viale del Parco Mellini 84, 00136, Rome, Italy
5
INAF-Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, 00133, Rome, Italy
6
ICRANet-Minsk, Institute of Physics, National Academy of Sciences of Belarus, Nezalezhnasci Ave. 68-2, 220072, Minsk, Belarus
Received:
25
April
2025
Accepted:
2
June
2025
Published online:
8
July
2025
Decades of progress culminating in the optical interferometry developed in the Keck Observatory and VLT GRAVITY facility led to the determination of the mass of the compact object in Sgr A* in 
and firm limits on its angular momentum. The most straightforward interpretation of these observations is a Schwarzschild black hole (BH). Considering that the S cluster of stars orbiting the Galactic Center does not probe distances closer than 1400 its Schwarzschild radius, several alternatives were proposed. Among them the self-gravitating system of Dark Matter (DM) fermions (here referred to as X-fermion) having a quantum degenerate core and extended to non-degenerate isothermal halo. Application of this model to our Galaxy results in a bound on X-fermion mass 
keV. Upon accreting baryonic matter the degenerate fermionic core may collapse into a BH providing seeds to Active Galactic Nuclei (AGNs) and SuperMassive Black Holes (SMBHs). We address the implications of DM X-fermions with mass 
keV endowed with a large and negative chemical potential here evaluated on structure formation and its evolution with redshift. The Jeans mass of X-fermions peaks at 
at redshift 
, which sets the scale of galactic structures. The degenerate cores forming as early as 
are consistent with recent observations of the James Web Space Telescope (JWST) disclosing the Little Red Dots (LRDs) at cosmological redshifts 
harboring SMBHs in the range 
. Assuming that Sgr A* is not yet a BH, the lower limit on SMBH mass of and the corresponding upper limit on the X-fermion mass of 
keV are established, which acquires relevance given ongoing JWST observations of the Galactic Center and the planning of new accelerators for the scrutiny of DM in CERN.
© The Author(s) 2025
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