Search Results (123)

Space-based gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA) and Taiji, will observe GWs from $O\left({10}^8\right)$ galactic binary systems, allowing a completely unobscured view of the Milky Way structure. While previous studies have established theoretical expectations based on idealized data-analysis methods that use the true catalog of sources, we present an end-to-end analysis pipeline for inferring galactic structure parameters based on the detector output alone. We employ the GBSIEVER algorithm to extract GB signals from LISA Data Challenge data and develop a maximum likelihood approach to estimate a bulge-disk galactic model using the resolved GBs. We introduce a two-tiered selection methodology, combining frequency derivative thresholding and proximity criteria, to address the systematic overestimation of frequency derivatives that compromises distance measurements. We quantify the performance of our pipeline in recovering key Galactic structure parameters and the potential biases introduced by neglecting the errors in estimating the parameters of individual GBs. Our methodology represents a step forward in developing practical techniques that bridge the gap between theoretical possibilities and observational implementation. Full article

To clarify the problem of outer cold gas accretion onto disk galaxies, we performed the panoramic spectroscopy of six compact galaxy groups to search for intergalactic gas flows. The groups selected are partly known to possess HI data obtained in the 21 cm line, and most of them contain a member galaxy revealing decoupled kinematics of gas and stars and thus having recently experienced a gas accretion event. Fabry-Perot scanning interferometry performed at the Russian 6 m telescope has provided us with the group maps at H$\alpha$ emission-line intensity and with ionized-gas velocity maps. We detected several intergalactic ionized-gas flows and some tidal outer ionized-gas structures; but none of them can be a source of gas accretion onto neighboring galaxies with decoupled gas–star kinematics. Only in a single case, that of NGC 7465, we can relate the inner inclined gaseous disk with the outer gas inflow; but the origin of this gas stream remains unknown—it does not originate from the neighboring NGC 7463 or NGC 7464. Full article

A pioneering detailed comparative study of the dynamics of plasma flows generated by high-power nanosecond and high-intensity femtosecond laser pulses with similar fluences of up to $3\times {10}^4$ J/cm² is presented. The experiments were conducted on the petawatt laser facility PEARL using two types of high-power laser radiation: femtosecond pulses with energy exceeding 10 J and a duration less than 60 fs, and nanosecond pulses with energy exceeding 10 J and a duration on the order of 1 ns. In the experiments, high-velocity (>100 km/s) flows of «femtosecond» (created by femtosecond laser pulses) and «nanosecond» plasmas propagated in a vacuum across a uniform magnetic field with a strength over 14 T. A significant difference in the dynamics of «femtosecond» and «nanosecond» plasma flows was observed: (i) The «femtosecond» plasma initially propagated in a vacuum (no B-field) as a collimated flow, while the «nanosecond» flow diverged. (ii) The «nanosecond» plasma interacting with external magnetic field formed a quasi-spherical cavity with Rayleigh–Taylor instability flutes. In the case of «femtosecond» plasma, such flutes were not observed, and the flow was immediately redirected into a narrow plasma sheet (or «tongue») propagating across the magnetic field at an approximately constant velocity. (iii) Elongated «nanosecond» and «femtosecond» plasma slabs interacting with a transverse magnetic field broke up into Rayleigh–Taylor «tongues». (iv) The ends of these «tongues» in the femtosecond case twisted into vortex structures aligned with the ion motion in the external magnetic field, whereas the «tongues» in the nanosecond case were randomly oriented. It was suggested that the twisting of femtosecond «tongues» is related to Hall effects. The experimental results are complemented by and consistent with numerical 3D magnetohydrodynamic simulations. The potential applications of these findings for astrophysical objects, such as short bursts in active galactic nuclei, are discussed. Full article

The phenomenon of augmented gravity on the scale of galaxies, conventionally attributed to dark matter halos, is shown to possibly result from the incremental growth of galactic masses and radii over time. This approach elucidates the cosmological origins of the acceleration scale $a_0\approx c{H}_0/2\pi \approx {10}^{-10}$ ms⁻² at which galaxy rotation curves deviate from Keplerian behavior, with no need for new particles or modifications to the laws of gravity, i.e., it constitutes a new explanatory path beyond Cold Dark Matter (CDM) and Modified Newtonian Dynamics (MOND). Once one formally equates the energy density of the universe to the critical value ($\rho ={\rho }_c$) and the cosmic age to the reciprocal of the Hubble parameter ($t=H^{-1}$), independently of the epoch of observation, the result is the Zero-Energy condition for the cosmic fluid’s equation of state, with key repercussions for the study of dark energy since the observables can be explained in the absence of a cosmological constant. Furthermore, this mass-energy evolution framework is able to reconcile the success of CDM models in describing structure assembly at $z\lesssim 6$ with the unexpected discovery of massive objects at $z\gtrsim 10$. Models that feature a strong coupling between cosmic time and energy are favored by this analysis. Full article

Accurate knowledge of the fine structure of low-ionisation-stage heavy elements is crucial for plasma modelling in stellar astronomy, galactic evolution studies, and nucleosynthesis investigations. The experimental determination of atomic energy levels and transitions in these elements is essential for the meaningful interpretation of high-resolution astrophysical spectra obtained with modern telescopes, as theoretical calculations of transition wavelengths and strengths often lack sufficient accuracy. This article provides a brief review of the major challenges in empirical atomic structure investigations of the low-ionisation open d- and f-subshell elements, which have the most complex atomic spectra. Full article

We analyze three nearby spiral galaxies—NGC 1097, NGC 1566, and NGC 3627—using images from the DustPedia database in seven infrared bands (3.6, 8, 24, 70, 100, 160, and 250 μm). For each image, we perform photometric decomposition and construct a multi-component model, including a detailed representation of the spiral arms. Our results show that the light distribution is well described by an exponential disk and a Sérsic bulge when non-axisymmetric components are properly taken into account. We test the predictions of the stationary density wave theory using the derived models in bands, tracing both old stars and recent star formation. Our findings suggest that the spiral arms in all three galaxies are unlikely to originate from stationary density waves. Additionally, we perform spectral energy distribution (SED) modeling using the hierarchical Bayesian code HerBIE, fitting individual components to derive dust properties. We find that spiral arms contain a significant (>10%) fraction of cold dust, with an average temperature of approximately 18–20 K. The estimated fraction of polycyclic aromatic hydrocarbons (PAHs) declines significantly toward the galactic center but remains similar between the arm and interarm regions. Full article

In the past few decades, large universal structures have been found that challenge the homogeneity and isotropy expected in standard cosmological models. The largest of these, identified as the Hercules–Corona Borealis Great Wall, was found in 2014 in the northern galactic hemisphere in the redshift range of $1.6\le z\le 2.1$. Subsequent studies used an increasing gamma-ray burst database to show that the cluster was unlikely to have been caused by statistical sampling uncertainties. This study re-examines burst clustering in the northern galactic hemisphere using a recently developed methodology. Evidence is provided that the Hercules–Corona Borealis Great Wall cluster is larger than previously thought, with members potentially spanning the redshift range of $0.33\le z\le 2.43$. The extension of this cluster’s size does not appear to have been due to statistical variations or sampling biases. Full article

In theoretical investigations, various mechanisms have been put forward to explain the emergence of spiral patterns in galaxies. One of the few ways to find out the nature of spirals in a particular galaxy is to consider the so-called corotation radius, or corotation resonance. A distinctly defined corotation resonance is likely to indicate the existence of a spiral density wave, while the chaotic distribution of their positions may suggest a dynamic nature to the spiral structure. In this study, we analyzed measurements of the corotation radius obtained using several methods for three galaxies (NGC 3686, NGC 4321, and NGC 2403) that exhibit different morphologies of spiral structures. We also performed independent measurements to estimate the location of the resonance, which allowed us to determine whether each galaxy has a clear corotation radius position. This examination, along with other tests such as stellar age gradient, interlocking resonances, and the radial distribution of metallicity, enables us to understand the mechanism that may be responsible for the formation of spiral arms in the studied galaxies. Full article

High-redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z ≥ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact core and core-jet morphologies, with 35% having unresolved cores, 59% with core–jet structures, and only 6% with core–double jet morphology. Brightness temperatures are generally lower than expected for highly radiative sources. The jets’ proper motions are surprisingly slow compared to those of lower-redshift samples. We observe a high fraction of young and/or confined peak-spectrum sources, providing insights into early AGN evolution in dense environments during early cosmic epochs. The observed trends may reflect genuine evolutionary changes in AGN structure over cosmic time, or selection effects favoring more compact sources at higher redshifts. These results stress the complexity of high-redshift radio-loud AGN populations and emphasize the need for multi-wavelength, high-resolution observations to fully characterize their properties and evolution through cosmic history. Full article

In our previous work, we investigated the spectra and anisotropy of galactic cosmic rays (GCRs) under the assumption of an axisymmetric distribution of galactic sources. Currently, much observational evidence indicates that the Milky Way is a typical spiral galaxy. In this work, we further utilize an anisotropic propagation model under the framework of spiral distribution sources to study spectra and anisotropy. During the calculation process, we adopt the spatial-dependent propagation (SDP) model, while incorporating the contribution from the nearby Geminga source and the anisotropic diffusion of cosmic rays (CRs) induced by the local regular magnetic field (LRMF). By comparing the results of background sources with spiral and axisymmetric distribution models, it is found that both of them can well reproduce the CR spectra and anisotropy. However, there exist differences in their propagation parameters. The diffusion coefficient with spiral distribution is larger than that with axisymmetric distribution, and its spectral indices are slightly harder. To investigate the effects of a nearby Geminga source and LRMF on anisotropy, two-dimensional (2D) anisotropy sky maps under various contributing factors are compared. Below 100 TeV, the anisotropy is predominantly influenced by both the nearby Geminga source and the LRMF, causing the phase to align with the direction of the LRMF. Above 100 TeV, the background sources become dominant, resulting in the phase pointing towards the Galactic Center (GC). Future high-precision measurements of CR anisotropy and spectra, such as the LHAASO experiment, will be crucial in evaluating the validity of our proposed model. Full article

The physical origin of the Blazhko effect (BL), a phenomenon of a single or multiple periodic modulation(s) of the light curve, is under debate. Efficiently identifying and characterizing the BL is essential in understanding its origins and accounting for its effect on numerous applications of RRabs in the era of large time-domain surveys. In this study, we make use of Resnet 34, a well-known convolutional neural network (CNN) architecture, to identify RRab stars with BL from phased light curves collected from OGLE. Using reliably classified RRabs from frequency analysis to train, validate, and test our model, we show that our CNN method reaches accuracies up to 94%. We then applied our CNN method to some additional RRabs located in the Magellanic Cloud (MC) and the Galactic Bulge (GB), leading to the discovery of 113 and 2496 BL candidates, respectively. The identification accuracy for the MC Sample is estimated to be 91% after cross-matching the CNN classification results with those from frequency analysis. Similarly, the light-curve parameters of these classified BL/non-BL candidates by our CNN method from the GB region resemble those observed in the literature, confirming the reliability of our CNN classifications. Our CNN method is subject to issues related to light-curve quality and sampling, but its overall reliance on light-curve quality is comparable to that of frequency analysis. Furthermore, we find that BL modulation could be primarily characterized by variations in light-curve structure. Full article

This paper presents a preliminary investigation into the influence of radial behavior of disk outflow on the structure and dynamics of the broad line region (BLR) in active galactic nuclei (AGNs), with an emphasis on how the mass ejection rate contributes to shaping the broad emission-line profiles. Specifically, we analyze how varying the radial efficiency of mass loss from accretion disks, driven by radiative dust-based mechanisms, contributes to the distribution of material in the BLR. By exploring different radial scenarios of disk mass loss behavior, we uncover connections between outflow radial efficiency and emission line profiles, particularly for lowly ionized lines. Our findings reveal that while the observed shape of broad emission lines is partially influenced by the radial behavior of the disk outflow, it ultimately depends more critically on the physical conditions of the clouds and the specific approach adopted regarding the emissivity for their contribution to the line formation. Full article

Accretion and migration usually proceed concurrently for giant planet formation in the natal protoplanetary disks. Recent works indicate that the concurrent accretion onto a giant planet imposes significant impact on the planetary migration dynamics in the isothermal regime. In this work, we carry out a series of 2D global hydrodynamical simulations with Athena++ to explore the effect of thermodynamics on the concurrent accretion and migration processes of the planets in a self-consistent manner. The thermodynamics effect is modeled with a thermal relaxation timescale using a $\beta$-cooling prescription. Our results indicate that radiative cooling has a substantial effect on the accretion and migration processes of the planet. As cooling timescales increase, we observe a slight decrease in the planetary accretion rate, and a transition from the outward migrating into inward migration. This transition occurs approximately when the cooling timescale is comparable to the local dynamical timescale ($\beta \sim 1$), which is closely linked to the asymmetric structures from the circumplanetary disk (CPD) region. The asymmetric structures in the CPD region which appear with an efficient cooling provide a strong positive torque driving the planet migrate outward. However, such a positive torque is strongly suppressed, when the CPD structures tend to disappear with a relatively long cooling timescale ($\beta \gtrsim 10$). Our findings may also be relevant to the dynamical evolution of accreting stellar-mass objects embedded in disks around active galactic nuclei. Full article

Supermassive black holes (SMBHs) are observed in active galactic nuclei interacting with their environments, where chaotical, discontinuous accretion episodes may leave matter remnants orbiting the central attractor in the form of sequences of orbiting toroidal structures, with strongly different features as different rotation orientations with respect to the central Kerr BH. Such ringed structures can be characterized by peculiar internal dynamics, where co-rotating and counter-rotating accretion stages can be mixed and distinguished by tori interaction, drying–feeding processes, screening effects, and inter-disk jet emission. A ringed accretion disk (RAD) is a full general relativistic model of a cluster of toroidal disks, an aggregate of axi-symmetric co-rotating and counter-rotating disks orbiting in the equatorial plane of a single central Kerr SMBH. In this work, we discuss the time evolution of a ringed disk. Our analysis is a detailed numerical study of the evolving RAD properties formed by relativistic thin disks, using a thin disk model and solving a diffusion-like evolution equation for an RAD in the Kerr spacetime, adopting an initial wavy (ringed) density profile. The RAD reaches a single-disk phase, building accretion to the inner edge regulated by the inner edge boundary conditions. The mass flux, the radial drift, and the disk mass of the ringed disk are evaluated and compared to each of its disk components. During early inter-disk interaction, the ring components spread, destroying the internal ringed structure and quickly forming a single disk with timescales governed by ring viscosity prescriptions. Different viscosities and boundary conditions have been tested. We propose that a system of viscously spreading accretion rings can originate as a product of tidal disruption of a multiple stellar system that comes too close to an SMBH. Full article

Two enigmatic gamma-ray features in the galactic central region, known as Fermi Bubbles (FBs), were found from Fermi-LAT data. An energy release, (e.g., by tidal disruption events in the Galactic Center, GC), generates a cavity with a shock that expands into the local ambient medium of the galactic halo. A decade or so ago, a phenomenological model of the FBs was suggested as a result of routine star disruptions by the supermassive black hole in the GC which might provide enough energy for large-scale structures, like the FBs. In 2020, analytical and numerical models of the FBs as a process of routine tidal disruption of stars near the GC were developed; these disruption events can provide enough cumulative energy to form and maintain large-scale structures like the FBs. The disruption events are expected to be ${10}^{-4}\sim {10}^{-5}{\mathrm{yr}}^{-1}$, providing an average power of energy release from the GC into the halo of $\dot{\mathcal{E}}\sim 3\times {10}^{41}$ erg ${\mathrm{s}}^{-1}$, which is needed to support the FBs. Analysis of the evolution of superbubbles in exponentially stratified disks concluded that the FB envelope would be destroyed by the Rayleigh–Taylor (RT) instabilities at late stages. The shell is composed of swept-up gas of the bubble, whose thickness is much thinner in comparison to the size of the envelope. We assume that hydrodynamic turbulence is excited in the FB envelope by the RT instability. In this case, the universal energy spectrum of turbulence may be developed in the inertial range of wavenumbers of fluctuations (the Kolmogorov–Obukhov spectrum). From our model we suppose the power of the FBs is transformed partly into the energy of hydrodynamic turbulence in the envelope. If so, hydrodynamic turbulence may generate MHD fluctuations, which accelerate cosmic rays there and generate gamma-ray and radio emission from the FBs. We hope that this model may interpret the observed nonthermal emission from the bubbles. Full article