The Sun moves with respect to the local interstellar medium (LISM) and modifies its properties to heliocentric distances as large as 1 pc. The solar wind (SW) is affected by penetration of the LISM neutral particles, especially H and He atoms. Charge exchange between the LISM atoms and SW ions creates pickup ions (PUIs) and secondary neutral atoms that can propagate deep into the LISM. Neutral atoms measured at 1 au can provide us with valuable information on the properties of pristine LISM. Voyager 1 and 2 spacecraft perform in situ measurements of the LISM perturbed by the presence of the heliosphere and relate them to the unperturbed region. We discuss observational data and numerical simulations that shed light onto the mutual influence of the SW and LISM. Physical phenomena accompanying the SW–LISM interaction are discussed, including the coupling of the heliospheric and interstellar magnetic field at the heliopause.

Thousands of ring-like bubbles appear on infrared images of the Galaxy plane. Most of these infrared bubbles form during expansion of Hii regions around massive stars. However, the physical effects that determine their morphology are still under debate. Namely, the absence of the infrared emission toward the centres of the bubbles can be explained by pushing the dust grains by stellar radiation pressure. At the same time, small graphite grains and PAHs are not strongly affected by the radiation pressure and must be removed by another process. Stellar ultraviolet emission can destroy the smallest PAHs but the photodestruction is ineffective for the large PAHs. Meanwhile, the stellar wind can evacuate all types of grains from Hii regions. In the frame of our chemo-dynamical model we vary parameters of the stellar wind and illustrate their influence on the morphology and synthetic infrared images of the bubbles.

The detection of an electromagnetic counterpart to the gravitational-wave source GW 170817 marked year zero of the multi-messenger gravitational-wave era. This event was generated by the merger of two neutron stars and gave rise to an electromagnetic transient, dubbed a “kilonova”. In this proceeding article, I will show how radiative transfer simulations can illuminate neutron star mergers and provide a connection between numerical models and observational data. I will present viewing-angle dependent kilonova predictions made with the Monte Carlo radiative transfer code POSSIS and show how these can be used to interpret data, place constraints on models and guide future follow-up campaigns of gravitational-wave triggers.

The hot accretion flow around Kerr black holes is strongly magnetized. Magnetic field loops sustained by a surrounding accretion disk can close within the event horizon. We performed particle-in-cell simulations in Kerr metric to capture the dynamics of the electromagnetic field and of the ambient collisionless plasma in this coupled configuration. We find that a hybrid magnetic topology develops with a closed magnetosphere co-existing with open field lines threading the horizon reminiscent of the Blandford-Znajek solution. Further in the disk, highly inclined open magnetic field lines can launch a magnetically-driven wind. While the plasma is essentially force-free, a current sheet forms above the disk where magnetic reconnection produces macroscopic plasmoids and accelerates particles up to relativistic Lorentz factors. A highly dynamic Y-point forms on the furthest closed magnetic field line, with episodic reconnection events responsible for transient synchrotron emission and coronal heating.

In the first observed neutron star merger, GW170817, two dynamical components, mildly- and ultra-relativistic outflows were detected independently. The first component triggered a rapidly evolving thermal transient named macronova (kilonova), while the second caused an observed short GRB where the early gamma-ray signal was followed by a multi-wavelength afterglow. These two distinct components are typically modelled independently and the observational consequences of their interplay are hardly explored. Here we summarize the results of 3D special-relativistic simulations that we have used to investigate the consequences of jet propagation through a realistic environment. We show how the presence of a jet can lead to the macronova being brighter and bluer for on-axis observers in the first few days. Then we show the consequences on the interaction on the shape of the emerging jet. Finally, we will discuss how small scale features in the emerging jet structure can impact the best-fit afterglow parameters.

The dust properties of the line-of-sight materials in neutron star low-mass X-ray binaries (LMXBs) can be probed by X-ray observations and laboratory experiments. We use a Markov chain Monte Carlo (MCMC) method to conduct a spectral analysis of Chandra ACIS-S/HETG archival data of a sample of LMXBs, including GX 5-1 and GX 13+1. Our MCMC-based analysis puts constraints on the Si K-edge dust properties of the outflowing disk winds in this sample. Further X-ray observations of other LMXBs will help us better understand the grain features of dense outflows and accretion flows in neutron star binary systems.

The Radio Neutrino Observatory Greenland (RNO-G) is currently being deployed and it is currently gathering data. As a precursor and complementary detector to the future radio array of IceCube-Gen2 in Antarctica, it will explore mainly the Northern sky via in-ice radio detection technique. The total array configuration includes 35 radio stations and will be fully completed within three years from now. The antennas will register the radio signals produced by the Askaryan effect in cascades generated in ice by neutrinos. RNO-G’s scientific purpose is to detect UHE neutrinos at energies above 10 PeV. Due to the attenuation length of radio waves in ice (order of 1 km) the radio detection allows to address neutrino energies above several PeV. The detector will reach unprecedented sensitivity in the scale from tens of PeV up to EeV. Models predict GRBs induced by binary neutron star mergers as likely transient sources of such highly energetic neutrinos. The current study of NS-NS mergers will therefore possibly be complemented by future RNO-G detections through multimessenger temporal and spatial coincidence, including an alert system. In this presentation, we will describe the instrument capabilities and explore the possibility of detection of such sources with RNO-G.

The Earth’s atmosphere is incessantly bombarded by energetic charged particles called cosmic rays (CR) which are having either solar or non-solar origin. Analysis based on information theoretic estimators can be effectively employed as a potential technique to analyze the dynamical changes in cosmic ray intensity during different solar cycles. In the present study, dynamical complexity based analysis using Jensen-Shannon divergence (JSD) has been employed which reveals the existence of some peculiar fluctuation properties in CRI flux at Jung neutron monitor station. JSD based dynamical complexity analyses confirm the existence of difference in dynamical properties of CR flux during solar cycles 20-21 and 22-23.

Multiphase outflows driven by active galactic nuclei (AGN) have a profound impact on the evolution of their host galaxies. The effects of AGN feedback are especially prominent in the brightest cluster galaxies (BCGs) of cool-core clusters, where there is a concentration of gas in all phases, ranging from cold molecular gas to hot, >107 K ionized plasma. In this proceeding I describe recent simulation efforts to understand the formation and evolution of the 10-kpc-scale Hα-emitting filaments driven by AGN activities. Combined with observed star formation regions co-spatial with the filaments, this feedback mechanism can directly contribute to the growth of the central galaxy, albeit delayed by the characteristic radiative cooling timescale, ∼10 Myr, of the outflowing plasma.

The evolution of the magnetic field in neutron star crusts because of the Hall effect has received significant attention over the last two decades, which is strongly justified because of the dominance of this effect in highly magnetised neutron stars. However, the applicability of the Hall effect is based on the assumption that the crust does not fail and sustains its rigidity. This assumption can be violated for substantially strong magnetic fields. If this is the case, the evolution of the magnetic field is described by a different set of equations, which include the effects of a non-rigid crust. In this talk, after a brief review of the main characteristic of the Hall evolution, I will discuss the impact a plastic flow of the crust has on the magnetic field, studying axisymmetric models. Moreover, the way the crust fails impacts the overall evolution, with major differences appearing if the failure is local, intermediate or global. Quite remarkably, crustal failure and plasticity do not annul the Hall effect, and under certain circumstances they may even lead to a more dramatic evolution. I will discuss the impact of these effects in the context of neutron star timing behaviour, with special focus on timing noise, outbursts and glitches.

We compare the properties of shocked gas in Sgr B2 with maps obtained from 3D simulations of a collision between two fractal clouds. In agreement with 13CO(1-0) observations, our simulations show that a cloud-cloud collision produces a region with a highly turbulent density substructure with an average . Similarly, our numerical multi-channel shock study shows that colliding clouds are efficient at producing internal shocks with velocities of 5 − 50 km s−1 and Mach numbers of ∼ 4 − 40, which are needed to explain the ∼ 10−9 SiO abundances inferred from our SiO(2-1) IRAM observations of Sgr B2. Overall, we find that both the density structure and the shocked gas morphology in Sgr B2 are consistent with a Myr-old cloud-cloud collision. High-velocity shocks are produced during the early stages of the collision and can ignite star formation, while moderate- and low-velocity shocks are important over longer time-scales and can explain the extended SiO emission in Sgr B2.

Stars form in clusters, while planets form in gaseous disks around young stars. Cluster dissolution occurs on longer time scales than disk dispersal. Planet formation thus typically takes place while the host star is still inside the cluster. We explore how the presence of other stars affects the evolution of circumstellar disks. Our numerical approach requires multi-scale and multi-physics simulations where the relevant components and their interactions are resolved. The simulations start with the collapse of a turbulent cloud, from which stars with disks form, which are able to influence each other. We focus on the effect of extinction due to residual cloud gas on the early evolution of circumstellar disks. We find that this extinction protects circumstellar disks against external photoevaporation, but these disks then become vulnerable to dynamic truncation by passing stars. We conclude that circumstellar disk evolution is heavily affected by the early evolution of the cluster.

Scientific synergies between Athena and some of the key multi-messenger facilities that should be operative concurrently with Athena are presented. These facilities include LIGO A+, Advanced Virgo+ and future detectors for ground-based observation of gravitational waves (GW), LISA for space-based observations of GW, IceCube and KM3NeT for neutrino observations, CTA for very high energy observations. Multimessenger synergy science themes discussed here include pressing issues in the field of Astrophysics, Cosmology and Fundamental physics such as: the central engine and jet physics in compact binary mergers, accretion processes and jet physics in SMBBHs and in compact stellar binaries, the equation of state in neutron stars, cosmic accelerators and the origin of cosmic rays, the origin of intermediate and high-Z elements in the Universe, the Cosmic distance scale and tests of General Relativity and Standard Model. Observational strategies for implementing the identified science topics are also discussed.

Computational heliophysics has shed light on the fundamental physical processes inside the Sun, such as the differential rotation, meridional circulation, and dynamo-generation of magnetic fields. However, despite the substantial advances, the current results of 3D MHD simulations are still far from reproducing helioseismic inferences and surface observations. The reason is the multi-scale nature of the solar dynamics, covering a vast range of scales, which cannot be solved with the current computational resources. In such a situation, significant progress has been achieved by the mean-field approach, based on the separation of small-scale turbulence and large-scale dynamics. The mean-field simulations can reproduce solar observations, qualitatively and quantitatively, and uncover new phenomena. However, they do not reveal the complex physics of large-scale convection, solar magnetic cycles, and the magnetic self-organization that causes sunspots and solar eruptions. Thus, developing a synergy of these approaches seems to be a necessary but very challenging task.

The hosts of binary neutron star (BNS) mergers and hence short GRBs are not only galaxies with old stellar populations, infact most short GRB hosts are at least mildly star-forming galaxies. According to theoretical studies of merger populations, both short and long merging time-scales are expected. The immediate environments of BNS mergers are not as directly related to the property of the progenitor system as for long GRBs, since the system usually travelled a significant distance from their birth place. However, studying the stellar population properties across the host can still give us vital information on the contribution of formation channels and on merger timescales. Here we review the properties of NS merger hosts in emission using integrated-light and resolved observations. The afterglows of short GRBs furthermore serve to study the interstellar medium in their host galaxies in absorption. We present our best example to date, GRB 160410A at z = 1.7, one of the highest redshift short GRBs.

We join gravitational-wave and electromagnetic data to implement a combined simultaneous fit of the GW170817 event. The LIGO-Virgo analysis includes the estimation of the inclination, the angle of the binary with respect to the gravitationa-wave detector network line of sight. From the observations of the afterglow, instead, we can recover the viewing angle. The inclination and the viewing angle are supplementary angles, and can be treated as a single parameter. The value of the inclination that we recover from the fit is in agreement with the LIGO-Virgo previous works, with an uncertainty that is 10-fold smaller, thanks to contribution of the electromagnetic data. Moreover, with the inclusion of the gravitational-wave data, the degeneracy between the viewing angle and the jet opening angle is broken. This procedure is useful not only for analyzing GW170817, but any gravitational-wave event with an electromagnetic counterpart.

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.