publications

2024

1. 

   Imaging fermionic dark matter cores at the centre of galaxies

   Joaquin Pelle, Carlos R. Argüelles , Florencia L. Vieyro , and 5 more authors

   Monthly Notices of the Royal Astronomical Society, Sep 2024

   Abs arXiv Bib PDF

   Current images of the supermassive black hole (SMBH) candidates at the center of our Galaxy and M87 have opened an unprecedented era for studying strong gravity and the nature of relativistic sources. Very-long-baseline interferometry (VLBI) data show images consistent with a central SMBH within General Relativity (GR). However, it is essential to consider whether other well-motivated dark compact objects within GR could produce similar images. Recent studies have shown that dark matter (DM) halos modeled as self-gravitating systems of neutral fermions can harbor very dense fermionic cores at their centers, which can mimic the spacetime features of a black hole (BH). Such dense, horizonless DM cores can satisfy the observational constraints: they can be supermassive and compact and lack a hard surface. We investigate whether such cores can produce similar observational signatures to those of BHs when illuminated by an accretion disk. We compute images and spectra of the fermion cores with a general-relativistic ray tracing technique, assuming the radiation originates from standard α disks, which are self-consistently solved within the current DM framework. Our simulated images possess a central brightness depression surrounded by a ring-like feature, resembling what is expected in the BH scenario. For Milky Way-like halos, the central brightness depressions have diameters down to ∼35 μas as measured from a distance of approximately 8 kpc. Finally, we show that the DM cores do not possess photon rings, a key difference from the BH paradigm, which could help discriminate between the models.

   @article{pelle2024imaging,
     author = {Pelle, Joaquin and Argüelles, Carlos R. and Vieyro, Florencia L. and Crespi, Valentinca and Millauro, Carolina and Mestre, Martin and Reula, Oscar and Carrasco, Federico},
     title = {Imaging fermionic dark matter cores at the centre of galaxies},
     journal = {Monthly Notices of the Royal Astronomical Society},
     volume = {534},
     number = {2},
     pages = {1217--1226},
     year = {2024},
     publisher = {Oxford University Press},
     month = sep,
     issn = {0035-8711},
     doi = {10.1093/mnras/stae2152},
     url = {https://doi.org/10.1093/mnras/stae2152},
     eprint = {https://academic.oup.com/mnras/advance-article-pdf/doi/10.1093/mnras/stae2152/59159310/stae2152.pdf},
     arxiv = {2409.11229},
   }

2. 

   A Parameter Study of the Electromagnetic Signatures of an Analytical Mini-Disk Model for Supermassive Binary Black Hole Systems

   Kaitlyn Porter , Scott C Noble , Eduardo M Gutierrez , and 4 more authors

   Jun 2024

   Abs arXiv Bib PDF

   Supermassive black holes (SMBHs) are thought to be located at the centers of most galactic nuclei. When galaxies merge they form supermassive black hole binary (SMBHB) systems and these central SMBHs will also merge at later times, producing gravitational waves (GWs). Because galaxy mergers are likely gas-rich environments, SMBHBs are also potential sources of electromagnetic (EM) radiation. The EM signatures depend on gas dynamics, orbital dynamics, and radiation processes. The gas dynamics are governed by general relativistic magnetohydrodynamics (MHD) in a time-dependent spacetime. Numerically solving the MHD equations for a time-dependent binary spacetime is computationally expensive. Therefore, it is challenging to conduct a full exploration of the parameter space of these systems and the resulting EM signatures. We have developed an analytical accretion disk model for the mini-disks of an SMBHB system and produced images and light curves using a general relativistic ray-tracing code and a superimposed harmonic binary black hole metric. This analytical model greatly reduces the time and computational resources needed to explore these systems, while incorporating some key information from simulations. We present a parameter space exploration of the SMBHB system in which we have studied the dependence of the EM signatures on the spins of the black holes (BHs), the mass ratio, the accretion rate, the viewing angle, and the initial binary separation. Additionally, we study how the commonly used fast-light approximation affects the EM signatures and evaluate its validity in GRMHD simulations.

   @article{porter2024parameter,
     title = {A Parameter Study of the Electromagnetic Signatures of an Analytical Mini-Disk Model for Supermassive Binary Black Hole Systems},
     author = {Porter, Kaitlyn and Noble, Scott C and Gutierrez, Eduardo M and Pelle, Joaquin and Campanelli, Manuela and Schnittman, Jeremy and Kelly, Bernard J},
     year = {2024},
     month = jun,
     eprint = {2407.04089},
     archiveprefix = {arXiv},
     primaryclass = {astro-ph},
     arxiv = {2407.04089},
   }

3. 

   Accretion disks and relativistic line broadening in boson star spacetimes

   João Luís Rosa , Joaquin Pelle, and Daniela Pérez

   Physical Review D, Oct 2024

   Abs arXiv Bib PDF

   In this work, we analyze the observational properties of static, spherically symmetric boson stars with fourth and sixth-order self-interactions, using the Julia-based general-relativistic radiative transfer code Skylight. We assume the boson stars are surrounded by an optically thick, geometrically thin accretion disk. We use the Novikov-Thorne model to compute the energy flux, introducing a physically based accretion model around these boson star configurations. Additionally, we calculate the relativistic broadening of emission lines, incorporating a lamppost corona model where the relativistic effects arising from the boson star spacetime have been taken into consideration. Our results show distinct observational features between quartic-potential boson stars and Schwarzschild black holes, owing to the presence of stable circular orbits at all radii around the former. On the other hand, compact solitonic boson stars, which possess an innermost stable circular orbit, have observational features closely similar to black holes. This similarity emphasizes their potential as black-hole mimickers. However, the compact boson stars, lacking an event horizon, have complex light-ring structures that produce potentially observable differences from black holes with future generations of experiments.

   @article{rosa2024accretion,
     author = {Rosa, João Luís and Pelle, Joaquin and Pérez, Daniela},
     title = {Accretion disks and relativistic line broadening in boson star spacetimes},
     journal = {Physical Review D},
     volume = {110},
     number = {8},
     pages = {084068},
     year = {2024},
     month = oct,
     doi = {10.1103/PhysRevD.110.084068},
     url = {https://link.aps.org/doi/10.1103/PhysRevD.110.084068},
     publisher = {American Physical Society},
     arxiv = {2403.11540},
   }

2023

1. 

   The shadow of charged traversable wormholes

   Mário Raia Neto , Daniela Perez , and Joaquin Pelle

   International Journal of Modern Physics D, Jan 2023

   Abs arXiv Bib PDF

   We compute the shadow cast by a charged Morris-Thorne wormhole when the light source is a star located beyond the mouth which is opposite to the observer. First, we provide an extensive analysis of the geodesic properties of the spacetime, both for null and massive particles. The geometrical properties of this solution are such that independently of the viewing angle, some light rays always reach the observer. Additionally, the structure of the images is preserved among the different values of the charge and scales proportionally to the charge value.

   @article{neto2023shadow,
     title = {The shadow of charged traversable wormholes},
     author = {Neto, M{\'a}rio Raia and Perez, Daniela and Pelle, Joaquin},
     journal = {International Journal of Modern Physics D},
     volume = {32},
     number = {02},
     pages = {2250137},
     year = {2023},
     month = jan,
     publisher = {World Scientific},
     arxiv = {2210.14106},
   }

2. 

   Relativistic force-free models of the thermal X-ray emission in millisecond pulsars observed by NICER

   Federico Carrasco , Joaquin Pelle, Oscar Reula , and 2 more authors

   Monthly Notices of the Royal Astronomical Society, Apr 2023

   Abs arXiv Bib PDF

   Several important properties of rotation-powered millisecond pulsars (MSPs), such as their mass-radius ratio, equation of state and magnetic field topology, can be inferred from precise observations and modelling of their X-ray light curves. In the present study, we model the thermal X-ray signals originated in MSPs, all the way from numerically solving the surrounding magnetospheres up to the ray tracing of the emitted photons and the final computation of their light curves and spectra. The magnetosphere is solved by performing general relativistic force-free simulations of a rotating neutron star (NS) endowed with a simple centred dipolar magnetic field, for many different stellar compactness and pulsar misalignments. From these solutions, we derive an emissivity map over the surface of the star, based on the electric currents in the magnetosphere. In particular, the emission regions (ERs) are determined in this model by spacelike four-currents that reach the NS. We show that this assumption, together with the inclusion of the gravitational curvature on the force-free simulations, lead to non-standard ERs facing the closed-zone of the pulsar, in addition to other ERs within the polar caps. The combined X-ray signals from these two kinds of ERs (both antipodal) allow to approximate the non-trivial interpulses found in several MSPs light curves. Our modelled X-ray signals are compared against very accurate NICER observations of four target pulsars: PSR J043-4715, PSR J1231-1411, PSR J2124-3358, and PSR J0030 + 0451, achieving very good simultaneous fits for their light curves and spectral distributions.

   @article{carrasco2023relativistic,
     title = {Relativistic force-free models of the thermal X-ray emission in millisecond pulsars observed by NICER},
     author = {Carrasco, Federico and Pelle, Joaquin and Reula, Oscar and Vigan{\`o}, Daniele and Palenzuela, Carlos},
     journal = {Monthly Notices of the Royal Astronomical Society},
     volume = {520},
     number = {2},
     pages = {3151--3163},
     year = {2023},
     month = apr,
     publisher = {Oxford University Press},
     arxiv = {2209.11674},
   }

2022

1. 

   Skylight: a new code for general-relativistic ray-tracing and radiative transfer in arbitrary space–times

   Joaquin Pelle, Oscar Reula , Federico Carrasco , and 1 more author

   Monthly Notices of the Royal Astronomical Society, Sep 2022

   Abs arXiv Bib PDF Code

   To reproduce the observed spectra and light curves originated in the neighborhood of compact objects requires accurate relativistic ray-tracing codes. In this work we present \textttSkylight, a new numerical code for general-relativistic ray tracing and radiative transfer in arbitrary space-time geometries and coordinate systems. The code is capable of producing images, spectra and light curves from astrophysical models of compact objects as seen by distant observers. We incorporate two different schemes, namely Monte Carlo radiative transfer integrating geodesics from the astrophysical region to distant observers, and camera techniques with backwards integration from the observer to the emission region. The code is validated by successfully passing several test cases, among them: thin accretion disks and neutron stars hot spot emission.

   @article{pelle2022skylight,
     title = {Skylight: a new code for general-relativistic ray-tracing and radiative transfer in arbitrary space--times},
     author = {Pelle, Joaquin and Reula, Oscar and Carrasco, Federico and Bederian, Carlos},
     journal = {Monthly Notices of the Royal Astronomical Society},
     volume = {515},
     number = {1},
     pages = {1316--1327},
     year = {2022},
     month = sep,
     publisher = {Oxford University Press},
     arxiv = {2206.06429},
   }