arXiv subjects

Jorge Cuadra

Publications and source records attributed to Jorge Cuadra.

At least 19 recordsLinked to original sources

arXiv2026

Interacting stellar winds feeding Sgr A*: from the system of mass-losing stars to the binary IRS 16SW

The discovery of cold structures around Sgr A* has challenged our understanding of the gas dynamics and thermodynamic state of the plasma in its vicinity. This work aims to constrain the conditions for the formation of such structures, namely the cold disc-like structure and the recently discovered G-1-2-3 complex. We conduct hydrodynamic simulations of the observed Wolf-Rayet stars feeding Sgr A*. Our simulations show that the plasma chemical composition is crucial for determining the medium properties. We demonstrate that the formation of a cold disc is possible for chemical compositions that are consistent with observational constraints. However, it is not possible to reproduce all the properties of the observed disc which might suggest the interaction with another structure. Additionally, we present our first results on the hydrodynamic modelling of IRS 16SW as a colliding-wind binary. This is the first step to develop a realistic model on the formation of the G-1-2-3 complex.

astro-ph.GA↗

arXiv2026

Superdiffusion at the Galactic Centre

Tracking S-star cluster orbits around Sgr A* calibrates orbital transport models for space-borne gravitational wave detectors. Standard kinetic theories model this cluster via local Fokker-Planck equations, which predict that general relativistic precession halts angular momentum diffusion at the Schwarzschild barrier. Because inverse-square gravitational encounters generate a Holtsmark torque distribution with infinite variance, resonant relaxation operates as a space-fractional process governed by non-local L\'{e}vy flights. We simulate this superdiffusive continuous-time random walk using a Markov chain initialized with empirical S-star orbits, including the recently observd S301. Integro-differential fractional operators allow trajectories to cross regions of quenched local diffusion without density buildup at the barrier. Non-equilibrium regimes yield immediate linear flux growth, while secular tidal heating at periastron inflates stellar radii to shift disruption boundaries. Regularized backward integration of the fractional transport equation traces current phase space configurations back to initial deposition states, matching the energy requirements of the \emph{Fermi} bubbles. Relativistic precession does not suppress mass-ratio inspiral rates, which provides a model for event topologies in target galactic nuclei.

astro-ph.GA↗

arXiv2026

Stellar rotation of S301 as a macroscopic gyroscope to test general relativity

Stellar trajectories around the Galactic Center provide a testing environment for general relativity. The intrinsic rotation of these stars evolves under covariant transport in curved spacetime and classical Newtonian quadrupole torques. We analyze the recently observed S301 S-star to quantify the relativistic precession of its rotational axis. Its 8.7-year period and eccentricity of $e = 0.982$ localize geodetic precession and Newtonian quadrupole torques to a step function at periapsis. We incorporate first-order post-Newtonian corrections into the orbital kinematics to calculate the spatial trajectory. Sampling an isotropic distribution of initial orientations and viewing geometries over a 40-year period across a grid of equatorial velocities and rotational ellipticities, we calculate the statistical likelihood of an absolute shift in the projected rotational line broadening, $|\Delta v \sin i|$. The relativistic geodetic shift scales linearly with $v_{\rm rot}$ and the classical quadrupole shift is independent of rotation speed, scaling with $q$. The absolute maximum velocity shift saturates at $46.1\,\kms$ for oblate stars. The absolute median shifts, driven by geodetic precession, range from $3\,\kms$ to $6.3\,\kms$. We calculate the time-domain observable $|\Delta v \sin i|$ to provide a target for infrared spectrographs testing the Schwarzschild metric around Sgr~A$^\ast$. The spin of S301 acts as a flying gyroscope whose drift, if measured, can test Einstein's theory in a regime that has not previously been accessible.

astro-ph.GA↗

arXiv2026

A positive period derivative in the quasi-periodic eruptions of ZTF19acnskyy

We report the first direct measurement of the period derivative in a quasi-periodic eruption (QPE), finding a smoothly increasing period with $\dot{P}\approx (1.7\pm 0.02)\times10^{-2}$ d d$^{-1}$ in the source ZTF19acnskyy/"Ansky". Most models for QPEs invoke repeated interactions of a stellar-mass orbiting companion around the supermassive black hole (SMBH) in an extreme mass-ratio inspiral (EMRI). In these scenarios, a positive $\dot{P}$ is surprising, but not impossible to produce. We explore several possible explanations for the observed $\dot{P}$, including stable mass-transfer driven by impulsive mass loss events in an EMRI, velocity kicks at pericenter due to tidal interactions with the SMBH, apparent period changes due either to general relativistic precession effects in an EMRI or light travel-time delays in a hierarchical SMBH binary, and mass-transfer variations in a thermal/viscous disk instability model. We find that none of the considered models provides a complete explanation for the data, motivating further work on physical explanations for positive period derivatives in QPEs.

astro-ph.HE↗

arXiv2025

Quantifying non-Gaussian diffusion in transient microscopy using excess kurtosis

Research on energy transport has advanced in recent years with the emergence of transient microscopy techniques that allow for imaging of carriers with high spatial and temporal resolution. In this context, transient scattering microscopy (TScM), has emerged as an alternative to traditional techniques. However, the sensitivity of TScM to different carriers can complicate the interpretation of results, highlighting the need to develop models tailored to TScM. Here, TScM is used to visualize exciton transport in bulk TMDCs. We show that exciton populations exhibit non-Gaussian profiles by analyzing the their excess kurtosis. Numerical simulations incorporating anomalous diffusion -- such as Auger recombination and trap states -- reproduce these experimental observations. Furthermore, by tuning the injected carrier density, we demonstrate that the temporal signature of the kurtosis is distinct for Auger-dominated and trap-dominated regimes. Additionally, we find that traditional Gaussian-fitting methods can yield inconsistent results for the extracted diffusivities. As an alternative, we implement a discrete variable calculation which yields robust, consistent diffusivity values. Our results establish kurtosis as a vital diagnostic parameter for identifying anomolous diffusion and demonstrate the necessity of moving beyond Gaussian approximations for accurate analysis of TScM data.

cond-mat.mtrl-sci↗

arXiv2025

Spin injection of exciton-polaritons with halide perovskites at room temperature

Exciton-polaritons, hybrid photon-exciton quasiparticles, constitute a useful platform for the study of light-matter interaction and nonlinear photonic applications. In this work, we realize a monolithic Tamm-plasmon microcavity embedding a thin film of two-dimensional halide perovskites with a tunable polymer spacer that controls the exciton-photon detuning. Angle-resolved optical spectroscopy at room temperature reveals the lower polariton branch dispersions in the linear regime for several detunings. Under circularly polarized, quasi-resonant laser excitation, the spin injection of excitons and their relaxation towards the lower polariton branch demonstrates its preservation. The observed spin-polarized emission is consistent with the fast decay of polaritons: spin relaxation mechanisms become inefficient during this short time. Our results provide promising insights into the spin control of polaritonic devices, including chiral lasers and switches.

cond-mat.mes-hall↗

arXiv2025

Signatures of edge states in antiferromagnetic van der Waals Josephson junctions

The combination of superconductivity and magnetic textures represents a promising approach to explore unconventional superconducting phenomena, including new correlated and topological phases. Van der Waals (vdW) materials have emerged in this context as a versatile platform to explore the interplay between these two competing orders. Here, we report on individual NbSe2/NiPS3/NbSe2 vdW Josephson junctions behaving as superconducting quantum interference devices (SQUIDs), which we attribute to the interplay between the superconductivity of NbSe2 and the spin texture of the vdW antiferromagnetic insulator NiPS3. The SQUID behavior, which persists for in-plane magnetic fields of at least 6 T, is the result of interference between localized transport channels that form in two separate regions of the sample. Microscopic modeling of the antiferromagnet insulator/superconductor (AFI/S) interface reveals the formation of localized states at the edges of the junction that can lead to localized channels that dominate the transport. Our findings highlight the potential of vdW superconducting heterostructures with AFs as platforms for engineering and probing novel superconducting phenomena, and they establish a new route for lithographic-free SQUIDs that operate in high magnetic fields.

cond-mat.supr-con↗

arXiv2025

Tidal phenomena in the Galactic Center: The curious case of X7

Several enigmatic dusty sources have been detected in the central parsec of the Galactic Center. Among them is X7, located at only $\sim$0.02 pc from the central super-massive black hole, Sagittarius A* (Sgr A*). Recent observations have shown that it is becoming elongated due to the tidal forces of Sgr A*. X7 is expected to be fully disrupted during its pericenter passage around 2035 which might impact the accretion rate of Sgr A*. However, its origin and nature are still unknown. We investigated the tidal interaction of X7 with Sgr A* in order to constrain its origin. We tested the hypothesis that X7 was produced by one of the observed stars with constrained dynamical properties in the vicinity of Sgr A*. We employed a set of test-particle simulations to reproduce the observed structure and dynamics of X7. The initial conditions of the models were obtained by extrapolating the observationally constrained orbits of X7 and the known stars into the past, making it possible to find the time and source of origin by minimizing the three-dimensional separation and velocity difference between them. Our results show that ejecta from the star S33/S0-30, launched in $\sim$1950, can to a large extent, replicate the observed dynamics and structure of X7, provided that it is initially elongated with a velocity gradient across it, and with an initial maximum speed of $\sim$600~km~s$^{-1}$. Our results show that a grazing collision between the star S33/S0-30 and a field object such as a stellar mass black hole or a Jupiter-mass object is a viable scenario to explain the origin of X7. Nevertheless, such encounters are rare based on the observed stellar dynamics within the central parsec.

astro-ph.GA↗

arXiv2025

Discovery of extreme Quasi-Periodic Eruptions in a newly accreting massive black hole

Quasi-periodic eruptions (QPEs) are rapid, recurring X-ray bursts from supermassive black holes, believed to result from interactions between accretion disks and surrounding matter. The galaxy SDSS1335+0728, previously stable for two decades, exhibited an increase in optical brightness in December 2019, followed by persistent Active Galactic Nucleus (AGN)-like variability for 5 years, suggesting the activation of a $\sim$10$^6\;M_\odot$ black hole. From February 2024, X-ray emission has been detected, revealing extreme $\sim$4.5-day QPEs with the highest fluxes and amplitudes, longest time scales, largest integrated energies, and a $\sim$25-day super-period. Low-significance UV variations are reported for the first time in a QPE host, likely related to the long timescales and large radii from which the emission originates. This discovery broadens the possible formation channels for QPEs, suggesting they are not linked solely to tidal disruption events but more generally to newly formed accretion flows, which we are witnessing in real time in a turn-on AGN candidate.

astro-ph.HE↗

arXiv2025

Ionized envelopes around protoplanets and the role of radiative feedback in gas accretion

Planetary growth within protoplanetary disks involves accreting material from their surroundings, yet the underlying mechanisms and physical conditions of the accreting gas remain debated. This study aims to investigate the dynamics and thermodynamic properties of accreting gas giants, and to characterize the envelope that forms near the planet during accretion. We employ three-dimensional hydrodynamical simulations of a Jupiter-mass planet embedded in a viscous gaseous disk. Our models incorporate a non-isothermal energy equation to compute gas and radiation energy diffusion and include radiative feedback from the planet. Results indicate that gas accretion occurs supersonically towards the planet, forming an ionized envelope that extends from the planetary surface up to 0.2 times the Hill radius in the no-feedback model, and up to 0.4 times the Hill radius in the feedback model. The envelope's radius, or ionization radius, acts as a boundary halting supersonic gas inflow and is pivotal for estimating accretion rates and H$α$ emission luminosities. Including radiative feedback increases accretion rates, especially within the ionization radius and from areas to the right of the planet when the star is positioned to the left. The accretion luminosities calculated at the ionization radius are substantially lower than those calculated at the Hill radius, highlighting potential misinterpretations in the non-detection of H$α$ emissions as indicators of ongoing planet formation.

astro-ph.EP↗

arXiv2025

The formation and stability of a cold disc made out of stellar winds in the Galactic Centre

The reported discovery of a cold (~10$^4$ K) disc-like structure within 0.005 pc around the super-massive black hole at the centre of the Milky Way, Sgr A*, has challenged our understanding of the gas dynamics and thermodynamic state of the plasma in its immediate vicinity. State-of-the-art simulations do not agree on whether or not such a disc can be a product of the multiple stellar wind interactions of the mass-losing stars in the region. This study aims to constrain the conditions for the formation of a cold disc as a natural outcome of the system of the mass-losing stars orbiting around Sgr A*, to investigate whether the disc is a transient or long-lasting structure, and to assess the validity of the model through direct comparisons with observations. We performed a set of hydrodynamic simulations of the observed Wolf-Rayet (WR) stars feeding Sgr A* using the finite-volume adaptive mesh refinement code Ramses. We focus, for the first time, on the impact of the chemical composition of the plasma emanating from the WR stars. The simulations show that the chemical composition of the plasma affects the radiative cooling enough to impact the properties of the medium, such as density and temperature, and, as a consequence, the rate at which the material inflows onto Sgr A*. We demonstrate that the formation of a cold disc from the stellar winds is possible for certain chemical compositions that are consistent with the current observational constraints. However, even in such cases, it is not possible to reproduce the reported properties of the observed disc-like structure, namely its inclination and the fluxes of its hydrogen recombination lines. We conclude that the stellar winds alone are not sufficient to form the cold disc around Sgr A* inferred from observations. Either relevant ingredients are still missing in the model, or the interpretation of the observed data needs to be revised.

astro-ph.GA↗

arXiv2024

Combining REBOUND and MESA: Dynamical Evolution of Planets Orbiting Interacting Binaries

Although planets have been found orbiting binary systems, whether they can survive binary interactions is debated. While the tightest-orbit binaries should host the most dynamically stable and long-lived circumbinary planetary systems, they are also the systems that are expected to experience mass transfer, common envelope evolution, or stellar mergers. In this study, we explore the effect of stable non-conservative mass transfer on the dynamical evolution of circumbinary planets. We present a new script that seamlessly integrates binary evolution data from the 1D binary stellar evolution code MESA into the N-body simulation code REBOUND. This integration framework enables a comprehensive examination of the dynamical evolution of circumbinary planets orbiting mass-transferring binaries, while simultaneously accounting for the detailed stellar structure evolution. In addition, we introduce a recalibration method to mitigate numerical errors from updates of binary properties during the system's dynamical evolution. We construct a reference binary model in which a $2.21\, M_\odot$ star loses its hydrogen-rich envelope through non-conservative mass transfer to the $1.76\, M_\odot$ companion star, creating a $0.38\,M_\odot$ subdwarf. We find the tightest stable orbital separation for circumbinary planets to be $\simeq 2.5$ times the binary separation after mass transfer. Accounting for tides by using the interior stellar structure, we find that tidal effects become apparent after the rapid mass transfer phase and start to fade away during the latter stage of the slow mass transfer phase. Our research provides a new framework for exploring circumbinary planet dynamics in interacting binary systems.

astro-ph.EP↗

arXiv2024

Multiwavelength Galactic Center gamma-ray observations explained by a unified cosmic-ray dynamics model

High-energy (HE) and very high-energy (VHE) gamma-ray observations from the Galactic center (GC) detected extended emission correlated with the morphology of the central molecular zone (CMZ). Emission in both bands is expected to be produced by hadronic interaction between cosmic rays (CRs) and ambient gas. We examine if our three previously proposed scenarios for the CR sources and dynamics, which are consistent with the VHE gamma-ray data (1-100 TeV), also match the HE gamma-ray observations (10-300 GeV). Additionally, we analyze the effect of the isotropic Galactic CR "sea" inside the CMZ. We generated synthetic gamma-ray maps considering a simplified isotropic diffusion, but more realistic dynamics with two diffusion zones (in and out of the CMZ) and polar advection, for mono-energetic particles of 3 TeV. Additionally, we considered two gas distributions for the CMZ (with and without an inner cavity), and CR populations injected from the clusters of young massive stars (the Arches Cluster, the Quintuplet Cluster, and the nuclear star cluster), plus the supernova Sgr A East. Only the combination of more realistic CR dynamics, the CMZ with an inner cavity, CR injection from all proposed sources, and a CR sea similar to that observed in the Solar System reproduced the current HE and VHE gamma-ray detection from the CMZ and was consistent with the observed gamma-rays from Sagittarius A*. The HE and VHE gamma-rays observations of the GC can be reproduced by a unified model for the CRs.}

astro-ph.HE↗

arXiv2024

The missing rings around Solar System moons

Rings are complex structures surrounding giant planets and some minor bodies in the Solar System. While some formation mechanisms could also potentially foster their existence around (regular or irregular) satellites, none of these bodies currently bear these structures. We aim to understand the underlying mechanisms that govern the potential formation, stability, and/or decay of hypothetical circumsatellital rings (CSRs), orbiting the largest moons in the Solar System. This extends to the exploration of short-term morphological features within these rings, providing insights into the ring survival time-scales and the interactions that drive their evolution. To conduct this study, we use numerical N-body simulations under the perturbing influence of the host planet and other moon companions. We found that moons with a lower Roche-to-Hill radius can preserve their rings over extended periods. Moreover, the gravitational environment in which these rings are immersed influences the system's morphological evolution, inducing gaps through the excitation of eccentricity and inclination of constituent particles. Specifically, our results show that Iapetus' and Rhea's rings experience minimal variations in their orbital parameters, enhancing their long-term stability. This agrees with the hypothesis that some of the features of Iapetus and Rhea were produced by ancient ring systems, for example, the huge ridge in Iapetus equator as a result of a decaying ring. From a dynamical perspective, we found that there are no mechanisms that preclude the existence of CSRs and we attribute their current absence to non-gravitational phenomena. Effects such as stellar radiation, magnetic fields, and the influence of magnetospheric plasma can significantly impact the dynamics of constituent particles and trigger their decay, highlighing the importance of future studies on these effects.

astro-ph.EP↗

arXiv2024

Long-term Evolution of Binary Orbits Induced by Circumbinary Disks

Circumbinary disks are found in a variety of astrophysical scenarios, spanning binary star formation to accreting supermassive black hole binaries. The interaction with a circumbinary disk can yield opposite effects on the binary orbit leading to circularization, or exciting the eccentricity, widening the orbit or shrinking it and facilitating mergers. We present a new formalism for the long-term evolution of the disk-binary interaction based on the results of recent suites of hydrodynamic simulations, which resolve the complex geometry of the gas in the vicinity of the binary and fully account for the gravitational and accretion forces. We release a python package, \texttt{spindler}, that implements our model. We show that, unless the mass reservoir feeding the disk is comparable to the mass of the binary, accretion onto the binary depletes the disk mass before inducing a significant change in orbital separation or mass ratio. This finding implies that, in most scenarios, interaction with a circumbinary disk is not an efficient mechanism to shrink the orbit of the binary. However, as long as the mass of the disk is at least a few percent of the mass of the binary, the interaction can excite the eccentricity up to an equilibrium value, and induce a statistical correlation between mass ratio and eccentricity. We consider the applicability of our model to a variety of astrophysical scenarios: during star formation, in evolved stellar binaries, triples and in supermassive black hole binaries. We discuss the theoretical and observational implications of our predictions.

astro-ph.HE↗

arXiv2024

Multistructured accretion flow of Sgr A* I: Examination of a RIAF model

The extreme low-luminosity supermassive black hole Sgr A* provides a unique laboratory in which to test radiatively inefficient accretion flow (RIAF) models. Previous fits to the quiescent Chandra ACIS-S spectrum found a RIAF model with an equal inflow-outflow balance works well. In this work, we apply the RIAF model to the Chandra HETG-S spectrum obtained through the Chandra X-ray Visionary Program, which displays features suggestive of temperature and velocity structures within the plasma. A comprehensive forward model analysis accounting for the accretion flow geometry and HETG-S instrumental effects is required for a full interpretation of the quiescent Chandra HETG-S spectrum. We present a RIAF model that takes these effects into account. Our fits to the high-resolution gratings spectrum indicate an inflow balanced by an outflow ($s \sim 1$) alongside a temperature profile that appears shallower than what would be expected from a gravitational potential following $1/r$. The data require that the abundance of Iron relative to solar is $Z_{Fe} < 0.32 Z_\odot$ (90\% credible interval), much lower than the $2~Z_\odot$ metallicity measured in nearby late-type giants. While future missions like NewAthena will provide higher spectral resolution, source separation will continue to be a problem. Leveraging Chandra's unparalleled spatial resolution, which is not expected to be surpassed for decades, remains essential for detailed investigations of the densely populated Galactic Center in X-rays.

astro-ph.HE↗

arXiv2024

Multistructured accretion flow of Sgr A* II: Signatures of a Cool Accretion Disk in Hydrodynamic Simulations of Stellar Winds

Hydrodynamic simulations of the stellar winds from Wolf-Rayet stars within the Galactic Center can provide predictions for the X-ray spectrum of supermassive black hole Sgr A*. Herein, we present results from updated smooth particle hydrodynamics simulations, building on the architecture of Cuadra et al. (2015); Russell et al. (2017), finding that a cold gas disk forms around Sgr A* with a simulation runtime of 3500 years. This result is consistent with previous grid-based simulations, demonstrating that a cold disk can form regardless of numerical method. We examine the plasma scenarios arising from an environment with and without this cold disk, by generating synthetic spectra for comparison to the quiescent Fe K alpha Sgr A* spectrum from Chandra HETG-S, taken through the Chandra X-ray Visionary Program. We find that current and future X-ray missions are unlikely to distinguish between the kinematic signatures in the plasma in these two scenarios. Nonetheless, the stellar wind plasma model presents a good fit to the dispersed Chandra spectra within 1.5" of Sgr A*. We compare our results to the Radiatively Inefficient Accretion Flow (RIAF) model fit to the HETG-S spectrum presented in Paper I and find that the Bayesian model evidence does not strongly favor either model. With 9" angular resolution and high spectral resolution of the X-IFU, NewAthena will offer a clearer differentiation between the RIAF plasma model and hydrodynamic simulations, but only a future X-ray mission with arcsecond resolution will significantly advance our understanding of Sgr A*'s accretion flow in X-rays.

astro-ph.HE↗

arXiv2024

Evolution of rotating massive stars adopting a newer, self-consistent wind prescription at SMC metallicity

We use Geneva-evolution-code to run evolutionary tracks for stellar masses ranging from $20$ to $85$ $M_\odot$ at SMC metallicity ($Z=0.002$). We upgrade the recipe for stellar winds by adopting our self-consistent m-CAK prescription, which reduces the value of mass-loss rate by a factor between 2 and 6 depending on the mass range. The impact of our new winds is wide, and it can be divided between direct and indirect impact. For the most massive models ($60$ and $85$ $M_\odot$) with $\dot M\gtrsim2\times10^{-7}$ $M_\odot$ yr$^{-1}$, the impact is direct because lower mass loss make stars remove less envelope and therefore remain more massive and less chemically enriched at their surface at the end of their MS phase. For the less massive models ($20$ and $25$ $M_\odot$) with $\dot M\lesssim2\times10^{-8}$ $M_\odot$ yr$^{-1}$, the impact is indirect because lower mass loss make the stars keep high rotational velocities for a longer period of time, then extending the H-core burning lifetime and reaching the end of the MS with higher surface enrichment. Given that the conditions at the H-depletion change, the stars will lose more mass during their He-core burning stages anyways. For $M_\text{zams}=20$ to $40$ $M_\odot$, our models predict stars will evolve through the Hertzsprung gap, from O-type supergiants to BSG and finally RSG, with larger mass fractions of helium compared to old evolution models. New models also set down to $M_\text{zams}=85\,M_\odot$ the minimal initial mass required for a single star to become WR at metallicity $Z=0.002$. New values for $\dot M$ need to be complemented with upgrades in additional features such as convective core overshooting and distribution of rotational velocities, besides more detailed observations from projects such as XShootU, in order to provide a robust framework for the study of massive stars at low metallicity environments.

astro-ph.SR↗