Galaxies

We review the properties of Wide-Angle-Tail (WAT) radio sources. The WAT radio sources are powerful, bent radio sources typically associated with the dominant galaxy in a cluster or group. For the purpose of this review, we define the radio morphology properties of WATs as (1) a sudden jet-tail transition, (2) overall bending of the tails to one side, and (3) non-parallel tails. The mechanism for the rapid jet-tail transition is uncertain but it seems to occur near the transition from the host ISM to ICM. The jet-tail transition may make the jets easier to bend. The narrow range in radio luminosity can be understood if there is a minimum luminosity required to allow the jets to propagate undisturbed for tens of kpc and a maximum luminosity required to allow the jet disruption mechanism to act. WATs are typically hosted by the brightest cluster galaxies in clusters which are currently merging. Thus, WATs can be used as tracers of merging clusters. The merging produces large-scale bulk motions in the ICM which can provide sufficient ram pressure to bend the jets. We suggest that although the Lorentz force may not bend the jets in WATs, it may be relevant in other sources, e.g., protostellar jets. Full article

The link between black holes and star formation allows for us to draw a connection between black holes and the places and times when extraterrestrial intelligences (ETIs) had a greater chance of emerging. Within the context of the gap paradigm for black holes, we show that denser cluster environments that led to gas-rich mergers and copious star formation were places less compatible on average with the emergence of ETIs compared to isolated elliptical galaxies by almost two orders of magnitude. The probability for ETIs peaked in these isolated environments around 6 billion years ago and cosmic downsizing shifted the likelihood of ETIs emerging to galaxies with weak black hole feedback, such as in spiral galaxies, at late times. Full article

Galaxy number counts in the K-, H-, I-, R-, B- and U-bands from the Durham Extragalactic Astronomy and Cosmology catalogue could be well-fitted over their whole range using luminosity function (LF) parameters derived from the SDSS at the bright region and required only modest luminosity evolution with the steepening of the LF slope ($\alpha$), except for a sudden steep increase in the B-band and a less steep increase in the U-band at faint magnitudes that required a starburst evolutionary model to account for the excess faint number counts. A cosmological model treating Hubble expansion as an Einstein curvature required less correction at faint magnitudes than a standard $\mathrm{\Lambda }$CDM model, without requiring dark matter or dark energy. Data from DR17 of the SDSS in the g, i, r, u and z bands over two areas of the sky centred on the North Galactic Cap (NGC) and above the South Galactic Cap (SGC), with areas of 5954 and 859 sq. deg., respectively, and a combined count of 622,121 galaxies, were used to construct bright galaxy number counts and galaxy redshift/density plots within the limits of redshift $\le 0.4$ and mag $\le 20$. Their comparative densities confirmed an extensive void in the Southern sky with a deficit of 26% out to a redshift z ≤ 0.15. Although not included in the number count data set because of its incompleteness at fainter magnitudes, extending the SDSS redshift-number count survey to fainter and more distant galaxies with redshift ≤ 1.20 showed a secondary peak in the number counts with many QSOs, bright X-ray and radio sources, and evolving irregular galaxies with rapid star formation rates. This sub-population at redshifts of 0.45–0.65 may account for the excess counts observed in the B-band. Recent observations from the HST and James Webb Space Telescope (JWST) have also begun to reveal a high density of massive galaxies at high redshifts ($z>7$) with high UV and X-ray emissions, and future observations by the JWST may reveal the assembly of galaxies in the early universe going back to the first light in the universe. Full article

Z Canis Majoris is a fascinating early-type binary with a Herbig Be primary and a FU Orionis-type secondary. Both of the stars exhibit sub-arcsecond jet-like ejecta. In addition, the primary is associated with the extended jet as well as with the large-scale outflow. In this study, we investigate further the nature of the large-scale outflow, which has not been studied since its discovery almost three and a half decades ago. We present proper motion measurements of individual features of the large-scale outflow and determine their kinematical ages. Furthermore, with our newly acquired deep images, we have discovered additional faint arc-shaped features that can be associated with the central binary. Full article

With the increasing reliance of astronomy on multi-instrument and multi-messenger observations for detecting transient phenomena, communication among astronomers has become more critical. Apart from automatic prompt follow-up observations, short reports, e.g., GCN circulars and ATels, provide essential human-written interpretations and discussions of observations. These reports lack a defined format, unlike machine-readable messages, making it challenging to associate phenomena with specific objects or coordinates in the sky. This paper examines the use of large language models (LLMs)—machine learning models with billions of trainable parameters or more that are trained on text—such as InstructGPT-3 and open-source Flan-T5-XXL for extracting information from astronomical reports. The study investigates the zero-shot and few-shot learning capabilities of LLMs and demonstrates various techniques to improve the accuracy of predictions. The study shows the importance of careful prompt engineering while working with LLMs, as demonstrated through edge case examples. The study’s findings have significant implications for the development of data-driven applications for astrophysical text analysis. Full article

Opacity is a fundamental quantity for stellar modeling, and it plays an essential role throughout the life of stars. After gravity drives the collapse of interstellar matter into a protostar, the opacity determines how this matter is structured around the stellar core. The opacity explains how the radiation field interacts with the matter and how a major part of the energy flows through the star. It results from all the microscopic interactions of photons with atoms. Part of the momentum exchange between photons and atoms gives rise to radiative accelerations (specific to each type of atom), which are strongly involved in a second-order process: atomic diffusion. Although this process is a slow one, it can have a significant impact on stellar structure and chemical composition measurements. In this review, we discuss the way opacities are presently computed and used in numerical codes. Atomic diffusion is described, and the current status of the consideration of this process is presented. Full article

The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide. Full article

We study radial oscillations in non-rotating neutron stars by considering the unified equation of states (EoSs), which support the 2 M_⊙ star criterion. We solve the Sturm–Liouville problem to compute the 20 lowest radial oscillation modes and their eigenfunctions for a neutron star modeled with eight selected unified EoSs from distinct Skyrme–Hartree–Fock, relativistic mean field and quarkyonic models. We compare the behavior of the computed eigenfrequency for an NS modeled with hadronic to one with quarkyonic EoSs while varying the central densities. The lowest-order f-mode frequency varies substantially between the two classes of the EoS at 1.4 M_⊙ but vanishes at their respective maximum masses, consistent with the stability criterion $\partial M/\partial {\rho }_c>0$. Moreover, we also compute large frequency separation and discover that higher-order mode frequencies are significantly reduced by incorporating a crust in the EoS. Full article

We review the recent theoretical and observational developments concerning the interaction of the Large Magellanic Cloud (LMC) with the Milky Way and its neighbourhood. An emerging picture is that the LMC is a fairly massive companion (10–20% of the Milky Way mass) and just passed the pericentre of its orbit, likely for the first time. The gravitational perturbation caused by the LMC is manifested at different levels. The most immediate effect is the deflection of orbits of stars, stellar streams, or satellite galaxies passing in the vicinity of the LMC. Less well known but equally important is the displacement (reflex motion) of central regions of the Milky Way about the centre of mass of both galaxies. Since the Milky Way is not a rigid body, this displacement varies with the distance from the LMC, and as a result, the Galaxy is deformed and its outer regions (beyond a few tens kpc) acquire a net velocity with respect to its centre. These phenomena need to be taken into account at the level of precision warranted by current and future observational data, and improvements on the modelling side are also necessary for an adequate interpretation of these data. Full article

In this work, a perturbed system of the restricted three-body problem is derived when the perturbation forces are conservative alongside the corresponding mean motion of two primaries bodies. Thus, we have proved that the first and second types of periodic orbits of the rotating Kepler problem can persist for all perturbed two-body and circular restricted three-body problems when the perturbation forces are conservative or the perturbed motion has its own extended Jacobian integral. Full article

In this paper, we investigate a scalar field cosmological model of accelerating Universe with the simplest parametrization of the equation of state parameter of the scalar field. We use $H\left(z\right)$ data, pantheon compilation of SN Ia data and BAO data to constrain the model parameters using the ${\chi }^2$ minimization technique. We obtain the present values of Hubble constant $H_0$ as $66.2_{-1.34}^{+1.42}$, $70.7_{-0.31}^{+0.32}$ and $67.{74}_{-1.04}^{+1.24}$ for $H\left(z\right)$, $H\left(z\right)$ + Pantheon and $H\left(z\right)$ + BAO respectively. In addition, we estimate the present age of the Universe in a derived model $t_0=14.{38}_{-0.64}^{+0.63}$ for joint $H\left(z\right)$ and pantheon compilation of SN Ia data which has only $0.88\sigma$ tension with its empirical value obtained in Plank collaboration. Moreover, the present values of the deceleration parameter $q_0$ come out to be $-0.{55}_{-0.038}^{+0.031}$, $-0.{61}_{-0.021}^{+0.030}$ and $-0.{627}_{-0.025}^{+0.022}$ by bounding the Universe in the derived model with $H\left(z\right)$, $H\left(z\right)$ + Pantheon compilation of SN Ia and $H\left(z\right)$ + BAO data sets, respectively. We also have performed the state-finder diagnostics to discover the nature of dark energy. Full article

The convective envelopes of solar-type stars and the convective cores of intermediate- and high-mass stars share boundaries with stable radiative zones. Through a host of processes we collectively refer to as “convective boundary mixing” (CBM), convection can drive efficient mixing in these nominally stable regions. In this review, we discuss the current state of CBM research in the context of main-sequence stars through three lenses. (1) We examine the most frequently implemented 1D prescriptions of CBM—exponential overshoot, step overshoot, and convective penetration—and we include a discussion of implementation degeneracies and how to convert between various prescriptions. (2) Next, we examine the literature of CBM from a fluid dynamical perspective, with a focus on three distinct processes: convective overshoot, entrainment, and convective penetration. (3) Finally, we discuss observational inferences regarding how much mixing should occur in the cores of intermediate- and high-mass stars as well as the implied constraints that these observations place on 1D CBM implementations. We conclude with a discussion of pathways forward for future studies to place better constraints on this difficult challenge in stellar evolution modeling. Full article

The Kepler and TESS space missions significantly expanded our knowledge of what types of stars display flaring activity by recording a vast amount of super-flares from solar-like stars, as well as detecting flares from hotter stars of A-F spectral types. Currently, we know that flaring occurs in the stars as hot as B-type ones. However, the structures of atmospheres of hot B-A stars crucially differ from the ones of late types, and thus the occurrence of flaring in B-A type stars requires some extension of our theoretical views of flare formation and therefore a detailed study of individual objects. Here we present the results of our spectral and photometric study of HD 36030, which is a B9 V star with flares detected by the TESS satellite. The spectra we acquired suggest that the star is in a binary system with a low-mass secondary component, but the light curve lacks any signs of periodic variability related to orbital motion or surface magnetic fields. Because of that, we argue that the flares originate due to magnetic interaction between the components of the system. Full article

This review has two parts. The first one is devoted to the Barbier–Chalonge–Divan (BCD) spectrophotometric system, also known as the Paris spectral classification system. Although the BCD system has been applied and is still used for all stellar objects from O to F spectral types, the present account mainly concerns normal and ‘active’ B-type stars. The second part treats topics related to stellar rotation, considered one of the key phenomena determining the structure and evolution of stars. The first part is eminently observational. In contrast, the second part deals with observational aspects related to stellar rotation but also recalls some supporting or basic theoretical concepts that may help better understand the gains and shortcomings of today’s existent interpretation of stellar data. Full article

We study radio and X-ray emissions from intermediate-mass black holes (IMBHs) and explore the unified model for accretion and ejection processes. The radio band survey of IMBH (candidate) hosted galaxies indicates that only a small fraction (∼0.6%) of them are radio-band active. In addition, very long baseline interferometry observations reveal parsec-scale radio emission of IMBHs, further resulting in a lower fraction of actively ejecting objects (radio emission is produced by IMBHs other than hosts), which is consistent with a long quiescent state in the evolution cycle of IMBHs. Most (75%, i.e., 3 out of 4 samples according to a recent mini-survey) of the radio-emitting IMBHs are associated with radio relics and there is also evidence of dual radio blobs from episodic ejecting phases. Taking the radio emission and the corresponding core X-ray emission of IMBH, we confirm a universal fundamental plane relation (FMP) of black hole activity. Furthermore, state transitions can be inferred by comparing a few cases in XRBs and IMBHs in FMP, i.e., both radio luminosity and emission regions evolve along these state transitions. These signatures and evidence suggest an analogy among all kinds of accretion systems which span from stellar mass to supermassive black holes, hinting at unified accretion and ejection physics. To validate the unified model, we explore the correlation between the scale of outflows (corresponding to ejection powers) and the masses of central engines; it shows that the largest scale of outflows ${\widehat{LS}}_{\mathrm{out}}$ follows a power-law correlation with the masses of accretors $M_{\mathrm{core}}$, i.e., $log{\widehat{LS}}_{\mathrm{out}}=(0.73\pm 0.01)log{M}_{\mathrm{core}}-(3.34\pm 0.10)$. In conclusion, this work provides evidence to support the claim that the ejection (and accretion) process behaves as scale-invariant and their power is regulated by the masses of accretors. Full article

The optical and UV properties of radio-quiet (RQ) and radio-loud (RL, relativistically “jetted”) active galactic nuclei (AGN) are known to differ markedly; however, it is still unclear what is due to a sample selection and what is associated with intrinsic differences in the inner workings of their emitting regions. Chemical composition is an important parameter related to the trends of the quasar main sequence. Recent works suggest that in addition to physical properties such as density, column density, and ionization level, strong Feii emitters require very high metal content. Little is known, however, about the chemical composition of jetted radio-loud sources. In this short note, we present a pilot analysis of the chemical composition of low-z radio-loud and radio-quiet quasars. Optical and UV spectra from ground and space were combined to allow for precise measurements of metallicity-sensitive diagnostic ratios. The comparison between radio-quiet and radio-loud was carried out for sources in the same domain of the Eigenvector 1/main sequence parameter space. Arrays of dedicated photo-ionization simulations with the input of appropriate spectral energy distributions indicate that metallicity is sub-solar for RL AGN, and slightly sub-solar or around solar for RQ AGN. The metal content of the broad line-emitting region likely reflects a similar enrichment story for both classes of AGN not involving recent circum-nuclear or nuclear starbursts. Full article

The Fanaroff–Riley Class II radio galaxy Cygnus A hosts jets that produce radio emission, X-ray cavities, cocoon shocks, and X-ray hotspots, where the jet interacts with the ICM. Surrounding one hotspot is a peculiar “hole” feature, which appears as a deficit in X-ray emission. We used relativistic hydrodynamic simulations of a collimated jet interacting with an inclined interface between lobe and cluster plasma to model the basic processes that may lead to such a feature. We found that the jet reflects off of the interface into a broad, turbulent flow back out into the lobe, which is dominated by gas stripped from the interface at first and from the intracluster medium itself at later times. We produced simple models of X-ray emission from the ICM, the hotspot, and the reflected jet to show that a hole of emission surrounding the hotspot as seen in Cygnus A may be produced by Doppler de-boosting of the emission from the reflected jet, as seen by an observer with a sight line nearly along the axis of the outgoing material. Full article

If baryosynthesis is strongly nonhomogeneous, macroscopic regions with antibaryon excess can be created in the same process from which the baryonic matter is originated. This exotic possibility can become real, if the hints to the existence of antihelium component in cosmic rays are confirmed in the AMS02 experiment, indicating the existence of primordial antimatter objects in our Galaxy. Possible forms of such objects depend on the parameters of models of baryosynthesis and evolution of antimatter domains. We elaborate the formalism of analysis of evolution of antibaryon domain with the account for baryon-antibaryon annihilation at the domain borders and possible “Swiss cheese” structure of the domain structure. We pay special attention to evolution of various forms of high, very high and ultrahigh density antibaryon domains and deduce equations of their evolution in the expanding Universe. The proposed formalism will provide the creation of evolutionary scenarios, linking the possible forms and properties of antimatter bodies in our Galaxy to the mechanisms of nonhomogeneous baryosynthesis. Full article

We present here the East Asia to Italy Nearly Global VLBI (EATING VLBI) project. How this project started and the evolution of the international collaboration between Korean, Japanese, and Italian researchers to study compact sources with VLBI observations is reported. Problems related to the synchronization of the very different arrays and technical details of the telescopes involved are presented and discussed. The relatively high observation frequency (22 and 43 GHz) and the long baselines between Italy and East Asia produced high-resolution images. We present example images to demonstrate the typical performance of the EATING VLBI array. The results attracted international researchers and the collaboration is growing, now including Chinese and Russian stations. New in progress projects are discussed and future possibilities with a larger number of telescopes and a better frequency coverage are briefly discussed herein. Full article