arXiv subjects

Jorge Castelo Mourelle

Publications and source records attributed to Jorge Castelo Mourelle.

8 recordsLinked to original sources

arXiv2026

Dark-to-black super-accretion as a spin-imprinting mechanism for supermassive Kerr black holes

The existence of supermassive black holes with masses $M\gtrsim10^9\,M_{\odot}$ and large dimensionless spins $χ\sim0.9-0.99$ at high redshift remains a challenge to our understanding of the early Universe. In this work, we study the adiabatic co-evolution of a Kerr black hole seed surrounded by two ultralight scalar dark matter clouds occupying different bound states, and show that this configuration allows the black hole to grow into the supermassive mass range while imprinting a characteristic final spin. The evolution proceeds through two stages. During the first stage, a spherical cloud described by the $\ell=0$ mode is completely depleted through a runaway dark-to-black accretion mechanism on a timescale of hundreds of millions of years for boson masses $μ\sim10^{-18}-10^{-17}\,\mathrm{eV}$. Since the accreted material does not carry angular momentum, the black hole spin is universally driven to $χ\simeq0$, independently of its initial spin. Throughout this stage, the second cloud, described by the $\ell=m=1$ mode, remains in the superradiant regime with negligible evolution. However, once the first stage is completed, this cloud transitions to the accreting regime, rapidly transferring both mass and angular momentum to the black hole. Starting from $χ\simeq0$, the black hole spin increases until the evolution self-consistently saturates close to the threshold $χ_{\rm sat}$, defined by the condition $Ω_H(χ_{\rm sat})=μ$, on an e-folding timescale of thousands of years, orders of magnitude shorter than the first stage. This final saturation spin is largely independent of both the initial black hole spin and the mass of the secondary cloud, providing a spin-imprinting mechanism in which the primordial spin is first erased by spherical accretion and then reset to a value determined only by the boson mass and the final black hole mass.

astro-ph.CO↗

arXiv2026

Rotating Fermion-Boson Stars in $R$-squared Gravity

Fermion-boson stars are compact equilibrium configurations composed of ordinary fermionic matter and a bosonic dark component interacting only through gravity. Such systems provide a natural framework for exploring deviations from standard neutron-star models, including the possible accumulation of dark matter inside neutron stars, and may be relevant for compact objects near the low-mass black-hole gap. We construct static and uniformly rotating fermion-boson stars within the framework of $R$-squared $f(R)$ gravity, characterized by the functional form $f(R)=R+aR^{2}$, where $a$ is a positive parameter governing the effective mass scale from the scalar degree of freedom. The fermionic sector is modeled as a perfect fluid described by a tabulated equation of state at zero temperature, while the bosonic component is represented by a self-interacting complex bosonic field. Our results show that the scalar degree of freedom modifies the spatial distribution of both the bosonic field and the fermionic pressure, enlarges the domain of admissible equilibrium solutions, and increases the maximum supported masses relative to general relativity. Our models remain compatible with current astrophysical and gravitational-wave constraints, suggesting that fermion-boson stars in $R$-squared gravity offer a promising framework to investigate the combined effects of dark bosonic matter, rotation, and strong-field modifications of gravity in compact objects.

gr-qc↗

arXiv2026

Testing bosonic dark matter through white dwarf mass measurements

Mass estimates of white dwarfs via electromagnetic methods, often differ from those obtained through gravitational redshift measurements, in some cases with discrepancies ranging in $5-15\%$ across independent datasets. Although many of the discrepancies reported in large spectroscopic surveys and confirmed by high-precision techniques such as astrometric microlensing and wide-binary analyses may be attributable to thermal effects, model uncertainties or measurement errors prevent a complete description of some of the observations. Here, we explore an alternative explanation based on the presence of a gravitationally coupled bosonic scalar field that contributes to the stellar mass while remaining electromagnetically invisible. We construct stationary, static mixed configurations consisting of a white dwarf that presents a bosonic scalar field (dark matter) component, forming a composite white dwarf-boson star system. We explore families of solutions showing that a scalar field fraction $f_{\rm DM} \sim 5-15\%$ to the mass contribution can account for the observed redshift excess. Our models provide a physically motivated explanation for the mass bias, might offer new observational signatures, and allow us to place preliminary constraints on the mass and compactness of the scalar field configuration. Finally, using our theoretical framework in combination with Bayesian model selection we provide plausible bounds for the mass of the constituent (ultralight) bosonic particle.

astro-ph.HE↗

arXiv2025

Reproducing galactic rotation curves with a two-component bosonic dark matter model

Bosonic stars,hypothetical astrophysical entities, are generally categorized into two primary classes based on the nature of their constituent particles: Einstein Klein Gordon stars, made up of massive scalar bosons, and Proca stars, their vector ''cousins''. Depending on the boson masses and field frequencies, these objects may exhibit properties of diffuse, massive structures, with sizes comparable to or even exceeding those of galaxies. This concept has inspired the bosonic dark matter halo hypothesis, providing a theoretical framework to effectively model the dark matter content of galactic halos. In this paper we build on our previous work to explore the possibility of using vector and scalar bosons to model the components of galactic dark matter halos and subhalos in order to reproduce the observed rotation curves of galaxies. By employing diverse combinations of those bosonic dark matter models in conjunction with observable data for a sample of galaxies, we show that our two component dark matter approach notably improves the agreement between observations and theoretical predictions with respect to our previous investigation. Our framework may shed new light on the enduring mystery surrounding the apparent matter deficit observed in dwarf and spiral galaxies.

astro-ph.GA↗

arXiv2025

Spinning boson stars in nonlinear sigma models and Universal Relations

Boson stars are hypothetical compact objects derived from solutions of a self-gravitating complex scalar field. In this study, we extend the traditional models by generalizing the kinetic term of the scalar field to that of a nonlinear sigma model. Concretely, we obtain spinning boson star solutions for a family of models parametrized by the curvature of their two-dimensional target manifold, as well as for various self-interaction potentials. We derive the global properties and multipolar structure of these solutions as a function of both the curvature of the target space and the strength of self-interactions. Our results suggest that a nonzero curvature in the target manifold can have a significant impact on the structure of the solutions, allowing for a range of notably different masses and degrees of compactness. However, we find that the relations between different multipoles are consistent with those for the standard complex scalar stars, and hence the universality of such relations is extended to curved target spaces.

gr-qc↗

arXiv2025

Galactic Halos and rotating bosonic dark matter

Rotating bosonic dark matter halos are considered as potential candidates for modeling dark matter in galactic halos. These bosonic dark matter halos can be viewed as a dilute and very extended version of bosonic stars, and the methods used for the calculation and analysis of the latter objects can be directly applied. Bosonic stars, a hypothetical type of astrophysical objects, are categorized into two primary families, based on the nature of the particles composing them: Einstein-Klein-Gordon stars and Proca stars. We examine various models from both families and the rotation curves which their contribution induces in different galaxies, to identify the most plausible candidates that explain the flattening of orbital velocities observed in galactic halos. By exploring different combinations of our dark matter models with observable galactic features, we propose an interesting source to compensate for the apparent lack of matter in dwarf and spiral galaxies, providing a possible explanation for this longstanding astronomical puzzle.

astro-ph.GA↗

arXiv2024

Rotating Fermion-Boson Stars

Rotating fermion-boson stars are hypothetical celestial objects that consist of both fermionic and bosonic matter interacting exclusively through gravity. Bosonic fields are believed to arise in certain models of particle physics describing dark matter and could accumulate within neutron stars, modifying some of their properties and gravitational wave emission. Fermion-boson stars have been extensively studied in the static non-rotating case, exploring their combined stability and their gravitational radiation in binary mergers. However, stationary rotating configurations were yet to be found and investigated. The presence of a bosonic component could impact the development of the bar-mode instability in differentially rotating neutron stars. Therefore, the study of rotating fermion-boson stars has important implications for astrophysics, as they could provide a new avenue for the detection of gravitational waves. In addition, these objects may shed light on the behavior of matter under extreme conditions, such as those found in the cores of neutron stars, and explain any tension in the determination of the dense-matter equation of state from multi-messenger observations. In this work we study a new consistent method of constructing uniformly rotating fermion-boson stars and we analyse some of their main properties. These objects might offer alternative explanations for current observations populating the lower black-hole mass gap, as the $2.6 M_\odot$ compact object involved in GW190814.

gr-qc↗

arXiv2024

Universal Relations for Rotating Scalar and Vector Boson Stars

Bosonic stars represent a hypothetical exotic type of compact stellar objects that could be observed from the gravitational signal of coalescing binaries in current and future gravitational wave detectors. There are two main families of bosonic stars, which depend on the nature that governs the particles that build them: Einstein-Klein-Gordon and Proca Stars. We study the multipolar structure for both families of rotating objects, using realistic potentials with the aim of finding possible universal relations and, thus, a method that allows us to distinguish between these and other compact objects in the gravitational wave paradigm. We also show how certain relevant observables can be obtained for these hypothetical but well-motivated astrophysical objects.

gr-qc↗