A four-year sky survey with the use of the eROSITA telescope on board the Spektr-RG observatory will provide the best coverage in the soft (0.5–2 keV) and standard (2–10 keV) X-ray ranges, both in terms of sensitivity and angular resolution. We have analysed the possibility of detecting various types of isolated neutron stars with eROSITA. Among already known objects, eROSITA will be able to detect more than 160 pulsars, 21 magnetars, 7 central compact objects, all seven sources of the Magnificent Seven, and two other X-ray isolated neutron stars during the four-year survey mission.

We present a new algorithm to solve the equations of radiation hydrodynamics (RHD) in a frequency-integrated, two-moment formulation. Novel features of the algorithm include i) the adoption of a non-local Variable Eddington Tensor (VET) closure for the radiation moment equations, computed with a ray-tracing method, ii) support for adaptive mesh refinement (AMR), iii) use of a time-implicit Godunov method for the hyperbolic transport of radiation, and iv) a fixed-point Picard iteration scheme to accurately handle the stiff nonlinear gas-radiation energy exchange. Tests demonstrate that our scheme works correctly, yields accurate rates of energy and momentum transfer between gas and radiation, and obtains the correct radiation field distribution even in situations where more commonly used – but less accurate – closure relations like the Flux-limited Diffusion and Moment-1 approximations fail. Our scheme presents an important step towards performing RHD simulations with increasing spatial and directional accuracy, effectively improving their predictive capabilities.

Multidimensional mathematical analysis, like Machine Learning techniques, determines the different features of objects, which is difficult for the human mind. We create a machine learning model to predict galaxies’ detailed morphology (∼ 300000 SDSS-galaxies with z < 0.1) and train it on a labeled dataset defined within the Galaxy Zoo 2 (GZ2). We use convolutional neural networks (CNNs) to classify the galaxies into five visual types (completely rounded, rounded in-between, smooth cigar-shaped, edge-on, and spiral) and 34 morphological classes attaining >94% of accuracy for five-class morphology prediction except for the cigar-shaped (∼ 87%) galaxies.

The velocity-space distribution of the solar neighborhood stars shows complex substructures (moving groups) including the well-known Hercules stream. Recently, the Gaia observation revealed their detailed structures, but their origins are still in debate. We analyzed a high-resolution N-body simulation of a Milky Way (MW)-like galaxy. To find velocity-space distributions similar to that of the solar neighborhood stars, we used Kullback-Leibler divergence (KLD), which is a metric to measure similarities between probability distributions. The KLD analysis shows the time evolution and the spatial variation of the velocity-space distribution. Velocity-space distributions with small KLDs (i.e. high similarities) are frequently but not always detected around in the simulated MW. In the velocity-map with smallest KLD, the velocity-space substructures are made from bar resonances.

Fast Radio Bursts (FRBs) are millisecond-long bursts of radio emission of extragalactic origin. The nature or FRBs is still unknown. Whether all FRBs are representatives of the same source population, or whether multiple underlying populations exist, is also unknown. One class that stands out is that of the “repeaters”, i.e. FRBs from which multiple bursts have been detected. In these cases, appropriate models should be non-cataclysmic but yet being able to create powerful coherent radio emission. Magnetars are among those source types that are considered as possible explanation for (repeating) FRBs. This review will summarise the basic properties of FRBs and those of magnetars to provide a critical assessment of the possible physical connection between these classes of sources. We conclude that while magnetars may indeed be related to the FRB phenomenon, it is unlikely that they explain all FRBs, i.e. at least two classes of FRBs exist.

Based on our current high resolution direct N-body modelling of the Milky Way typical Star Cluster systems dynamical evolution we try to numerically estimate the influence of individual spin values and orientations on gravitational wave (GW) waveforms and observed time-frequency maps during multiple cycles for binary black hole (BBH) mergers. In our up to date N-body dynamical simulations we use the high order relativistic post-Newtonian corrections for the BH binary particles (3.5 post-Newtonian (PN) terms including spin-spin and spin-orbit terms). In the current work, we present the GW waveforms catalogue which covers the large parameter space in mass ratios 0.05 - 0.82 and extreme possible individual spin cases.

The magnetar SGR J1830–0645 was discovered in outburst in October 2020. We studied its X-ray properties during the first month of the outburst using XMM–Newton, NuSTAR and Swift observations. The shape and amplitude of the pulse profile varied significantly with energy. The broadband spectrum was well described using two absorbed blackbody components plus a faint power law component at high energies. Phase-resolved spectral analysis of the data suggests that the emission could be attributed to thermal photons from a single heated region with a complex shape on the star surface undergoing resonant Compton scattering on charged particles located in the magnetosphere. Modelling the evolutionary path of the magnetar with our magneto-thermal evolutionary codes indicates that SGR J1830 was born ≈23 kyr ago with a dipolar magnetic field of ∼1015 G, slightly larger than the current value.

We continue studying convection as a possible factor of episodic accretion in protoplanetary disks. Within the model of a viscous disk, the accretion history is analyzed at different rates and regions of matter inflow from the envelope onto the disk. It is shown that the burst-like regime occurs in a wide range of parameters. The long-term evolution of the disk is modeled, including the decreasing-with-time matter inflow from the envelope. It is demonstrated that the disk becomes convectively unstable and maintains burst-like accretion onto the star for several million years. The general conclusion of the study is that convection can serve as one of the mechanisms of episodic accretion in protostellar disks, but this conclusion needs to be verified using more consistent hydrodynamic models.

Due to the rich phenomenology and extreme magnetic conditions, magnetars will be targets of great interest for the upcoming polarimetry space missions. In particular, the Imaging X-ray Polarimetry Explorer (IXPE), recently launched in December 2021, will operate in the 2–8 keV range. This will open a new window to study the polarized, persistent X-ray emission from magnetars. In this talk, I will present simulations of IXPE observations of magnetars using the IXPEObsSim package. I will discuss future prospect to discriminate between different magnetar’s emission mechanisms, as well as a potential detection of the signal of vacuum birefringence using IXPE.

Thermal energies deposited by OB stellar clusters in starburst galaxies lead to the formation of galactic superwinds. Multi-wavelength observations of starburst-driven superwinds pointed at complex thermal and ionization structures which cannot adequately be explained by simple adiabatic assumptions. In this study, we perform hydrodynamic simulations of a fluid model coupled to radiative cooling functions, and generate time-dependent non-equilibrium photoionization models to predict physical conditions and ionization structures of superwinds using the maihem atomic and cooling package built on the program flash. Time-dependent ionization states and physical conditions produced by our simulations are used to calculate the emission lines of superwinds for various parameters, which allow us to explore implications of non-equilibrium ionization for starburst regions with potential radiative cooling.

We describe a numerical model of hot Jupiter extended envelope that interacts with stellar wind. Our model is based on approximation of multi-component magnetic hydrodynamic. The processes of ionization, recombination, dissosiation and chemical reactions in hydrogen-helium envelope are taken into account. In particular, the ionization of neutral hydrogen atoms takes place due to processes of photo-ionization, charge-exchange and thermal collisions. Further, this model is supposed to be used for research on biomarkers’ dynamics in extended envelopes of hot Jupiters.

The focus of this work is to comprehensively understand hydro-dynamical back-flows and their role in dynamics and non-thermal spectral signatures particularly during the initial phase of X-shaped radio galaxies. In this regard, we have performed axisymmetric (2D) and three dimensional (3D) simulations of relativistic magneto-hydrodynamic jet propagation from tri-axial galaxies. High-resolution dynamical modelling of axisymmetric jets has demonstrated the effect of magnetic field strengths on lobe and wing formation. Distinct X-shape formation due to back-flow and pressure gradient of ambient is also observed in our 3D dynamical run. Furthermore, the effect of radiative losses and diffusive shock acceleration on the particle spectral evolution is demonstrated, which particularly highlights how crucial their contributions are in the emission signature of these galaxies. This imparts a significant effect on the galaxy’s equipartition condition, indicating that one must be careful in extending its use in estimating other parameters, as the criterion evolves with time.

Pulsating Ultra Luminous X-ray sources (PULXs) are thought to be X-ray bright, accreting, magnetized neutron stars, and could be the first and only evidence for the existence of magnetars in binary systems. Their apparent soft (< 20 keV) X-ray luminosity can exceed the Eddington luminosity for a neutron star (NS) by a few orders of magnitude. Although several scenarios have been proposed to explain the different components observed in the X-ray spectra and the characteristics of the X-ray lightcurve of these system, detailed quantitative calculations are still missing. In particular, the observed soft X-ray lightcurves are almost sinuosidal and show an increase in the pulsed fraction (from 8% up to even 30%) with increasing energy. Here, we present how emission originating from an optically thick envelope, expected to be formed during super-Eddington accretion, can result in pulsed fractions similar to observations.

A detailed description of the properties of dense matter in extreme conditions, as those within Neutron Star cores, is still an open problem, whose solution is hampered by both the lack of empirical data, and by the difficulties in developing a suitable theoretical framework for the microscopic nuclear dynamics in such regimes.

We report here the results of a study aimed at inferring the properties of the repulsive three-nucleon interaction, driving the stiffness of the equation of state at high densities, by performing bayesian inference on current and future astrophysical observations.

The dense matter equation of state (EoS), describing the state of matter under the extreme conditions found in neutron stars, is not accurately known. However, significant process has been made in recent years through the emergence of new observational avenues of neutron stars. Firstly, the X-ray timing telescope NICER has delivered two joint mass-radius measurements, for pulsars PSR J0030+0451 and PSR J0740+6620, using pulse profile modeling. Secondly, gravitational wave detections of binary neutron star (BNS) mergers allow for a measurement of the EoS-dependent tidal deformability, as demonstrated in the first detected BNS merger GW170817. Additionally, electromagnetic radiation from the subsequent ultraviolet-optical-infrared transient (the kilonova) originating from the ejected material in GW170817 further probes the binary system and the EoS. We demonstrate how the joint analysis of these multi-messenger observations of neutron stars significantly constrains the dense matter EoS. We then describe, in more detail, a framework to jointly analyse a gravitational wave signal and the accompanying kilonova light curves, focusing on possible future black hole–neutron star (BHNS) mergers. We highlight the potential for multimessenger BHNS to constrain the tidal deformability of the neutron star, thereby increasing our understanding of the dense matter EoS.

Computational fluid dynamics is a crucial tool to theoretically explore the cosmos. In the last decade, we have seen a substantial methodological diversification with a number of cross-fertilizations between originally different methods. Here we focus on recent developments related to the Smoothed Particle Hydrodynamics (SPH) method. We briefly summarize recent technical improvements in the SPH-approach itself, including smoothing kernels, gradient calculations and dissipation steering. These elements have been implemented in the Newtonian high-accuracy SPH code MAGMA2 and we demonstrate its performance in a number of challenging benchmark tests. Taking it one step further, we have used these new ingredients also in the first particle-based, general-relativistic fluid dynamics code that solves the full set of Einstein equations, SPHINCS_BSSN. We present the basic ideas and equations and demonstrate the code performance at examples of relativistic neutron stars that are evolved self-consistently together with the spacetime.

In the neutron-star mergers, the radioactive decay of freshly synthesized heavy elements produces emissions in the ultraviolet-optical-infrared range, producing a transient called kilonova. The observational properties of the kilonova depend on the bound-bound opacity of the heavy elements, which was largely unavailable for the conditionssuitable at an early time (t < day). In this article, I share some of our recent progress on modeling the early kilonova light curve, focusing on the atomic opacity calculation.

One of the ways to understand the genesis and evolution of the universe is to know how galaxies have formed and evolved. In this regard, the study of star formation history (SFH) plays an important role in the accurate understanding of galaxies. In this paper, we used long-period variable stars (LPVs) for estimating the SFH in the Andromeda galaxy (M31). These cool stars reach their peak luminosity in the final stage of their evolution also their birth mass is directly related to their luminosity. Therefore, using stellar evolution models, we construct the mass function and hence the star formation history.

Situation with highly magnetized neutron stars in binary systems is not yet certain. On the one hand, all best studied magnetars seem to be isolated objects. On the other, there are many claims based on model-dependent analysis of spin properties or/and luminosity of neutron stars in X-ray binaries in favour of large fields. In addition, there are a few results suggesting a magnetar-like activity of neutron stars in close binary systems. Most of theoretical considerations do not favour even existence, not speaking about active decay, of magnetar-scale fields in neutron stars older than ∼106 yrs. However, alternative scenarios of the field evolution exist. I provide a brief review of theoretical and observational results related to the presence of neutron stars with large magnetic field in binaries and discuss perspectives of future studies.

We investigate the broad-band behaviour of circular polarization in radio pulsar profiles and show the relationship between polarization fraction and what proportion of that polarization is circular, both across frequency, and for a large number of pulsars viewed collectively. The behaviour observed may be explained by pulsar polarization originating from the partially-coherent combination of two linearly-polarized orthogonal modes with different flux spectral indices. (See also the poster in the “supplementary information”.)