Fuzzy Dark Matter in Relativistic Stars

TL;DR

The paper investigates how fuzzy dark matter (FDM) with observationally constrained microphysics affects the structure of relativistic stars by employing a two-fluid formalism that couples a visible-matter sector to a FDM sector. FDM is modeled as a scalar field with $V(\phi)=\frac{1}{2}m^{2}\phi^{2}+\frac{1}{4}\lambda\phi^{4}$, with cosmological data yielding $m\ge 10^{-24}\,\mathrm{eV}$ and $\log_{10}\lambda< -91.86+4\log_{10}(\frac{m}{10^{-22}\mathrm{eV}})$; the authors adopt $m=10^{-24}\mathrm{eV}$, $\lambda=10^{-100}$ and implement EoSs for neutron, quark, and hybrid matter constrained by GW170817, NICER, and LMXB data. They compute the mass–radius relations and tidal deformabilities for FDM-admixed NSs, QSs, and HSs, finding that FDM generally lowers maximum masses, makes stars more compact, and suppresses the dimensionless tidal deformability $\Lambda$, while remaining compatible with current observational bounds. These results highlight the potential imprint of FDM on compact-star observables and offer astrophysical avenues to constrain ultralight dark-matter models with current and future gravitational-wave and X-ray data.

Abstract

Fuzzy dark matter (FDM), a practical alternative to cold dark matter, can exist in compact stars. Here, applying the FDM equation of state (EoS) constrained by CMB and large-scale structure data, we calculate the structure of relativistic stars in the presence of FDM. For this aim, the EoS for the visible matter in neutron stars, quark stars, and hybrid stars from the observational data are employed. A piecewise polytropic EoS constrained by the observational data of GW170817 and the data of six low-mass X-ray binaries with thermonuclear burst or the symmetry energy of the nuclear interaction describes the neutron star matter. For quark star matter, we apply the EoSs within the Bayesian statistical approach using the mass and radius measurements of PSR J0030+0451 from NICER. Employing the two-fluid formalism, we study the structure of FDM admixed relativistic stars.

Figures (11)

• Figure 1: Fuzzy dark matter EoS with the parameters $m=10^{-24} eV$ and $\lambda=10^{-100}$ from the observational data.
• Figure 2: Left: EoS of dense neutron star matter constrained by the observational data and Right: Mass radius relation in the cases of neutron star (NS) and FDM admixed neutron star (FDMANS). Observational constraints on the NS radii and masses from the pulsars and the gravitational wave data are also presented. These constraints are related to NICER observations for PSR J0952-0607 Romani, PSR J2215+5135 Linares, PSR J0740+6620 CromartieFonsecaMiller21Riley, PSR J0030+0451 Miller, and the merger events GW170817 Abbott7Abbott8 and GW190814 Abbott.
• Figure 3: Mass radius relation for two sectors of neutron star matter ($M_N-R_N$) and dark matter ($M_D-R_D$) in FDMANS.
• Figure 4: Tidal Love number $k_2$, the value $y_R$, and the dimensionless tidal deformability $\Lambda$ versus the mass for NS and FDMANS. The constraints from GW170817 and GW190814 data (LIGO and Virgo Collaborations) for neutron star of mass $M = 1.4 M_{\odot}$ are also given. These upper limits on dimensionless tidal deformability are $\Lambda_{1.4}=190^{+390}_{-120}$ for GW170817 Abbott8 and $\Lambda_{1.4}=616^{+273}_{-158}$ for GW190814 Abbott.
• Figure 5: Three EoSs of quark star matter based on the bag models constraint with the NICER data.