The aim of a talk is to give an overview current state gravitational wave observations. During three science runs (2015-2016, 2016-2017, 2019-2020) of Advanced LIGO-Virgo detectors observe multiple binary merger events. Most of the events are binary black hole mergers, but nine detected events had neutron star component. Those observations, especially GW170817, brought additional way to study neutron stars. In the last part of the talk I would focus on multi-messenger astronomy that could be done and possible future challenges and opportunities in gravitational wave astronomy.

I will present an investigation of the accretion-induced spin-up of a black hole via numerical simulations. The method is based on general-relativistic hydrodynamics of the slowly-rotating flows in the Kerr metric, with change of mass and spin of the black hole during accretion taken into account. Simulations were performed using modified versions of HARM code. The aim of this study was to verify whether the high mass stellar black holes may be produced with large spins, even though at birth the collapsars might have contained non-spinning, or moderately-spinning cores.

Galaxies are subject to strong tidal evolution in the environment of clusters. I will discuss this process using the example of the most massive cluster of the IllustrisTNG-100 simulation that traces the formation and evolution of galaxies in the cosmological context. For the purpose of this work, I selected 112 galaxies in the cluster, with the largest stellar masses at present, and followed their properties over time. Using their orbital history, the sample is divided into unevolved (infalling), weakly evolved (with one pericenter passage), and strongly evolved (with multiple pericenters). The samples are clearly separated by the value of the integrated tidal force from the cluster the galaxies experienced during their entire evolution and their properties depend strongly on this quantity. As a result of tidal stripping, the galaxies lose mass and become significantly less dark matter dominated. The cluster environment is also very efficient in stripping the galaxies of their gas and quenching the star formation. The strongly evolved galaxies lose their gas earlier and faster, and they become redder and more metal rich, so that at redshift z=0.5 the population of galaxies in the cluster becomes predominantly red. As a result of tidal stirring, the morphology of the galaxies evolves from oblate to prolate and their rotation is diminished, thus the morphology-density relation is reproduced in the simulated cluster. The strongly evolved sample contains at least six convincing examples of tidally induced bars and six more galaxies that had their bars enhanced by their interaction with the cluster.

Light curves of astronomical objects, like active galactic nuclei or gamma-ray bursts (GRBs), often exhibit complex variability. Current instruments provide numerous high quality data, which allow to analyse them with novel methods both in the temporal and spectral domains. I will discuss some of these methods, and show the most recent results: investigation of power spectral densities using global periodograms and wavelet based approaches, as well as classification schemes of blazar and GRB light curves in the A-T plane.

Thousands of extrasolar planets have been discovered up to date. Although many of the known exoplanets do not resemble those in our solar system, they have one thing in common - they all orbit a star. However, theories of planet formation and evolution predict the existence of free-floating planets, gravitationally unattached to any star. Gravitational microlensing is uniquely suited for finding free-floating planets. I will present the current constraints on the frequency and properties of rogue planets in the Milky Way based on long-term observations of microlensing events in the Galactic bulge by the OGLE sky survey. I will also present several of the most promising candidate free-floating planets discovered to date. Finally, I will briefly discuss the future prospects for determining the frequency and mass function of rogue planets by the planned microlensing experiments.

Solar transients such as solar flares, coronal mass ejections (CMEs) and solar wind are topics that require utmost importance of research as they generate geomagnetic storms causing catastrophic damages to power grids on Earth and are serious radiation threat to satellites on low-Earth orbit and their crew during spacewalks. As a consequence of these powerful outbursts on the Sun, energetic protons and ions, known as solar energetic particles (SEPs), are accelerated at high speeds. The acceleration is mainly due to shocks induced by CMEs or at the magnetic reconnection regions of solar flares. As a practical consequence, Earth-directed (halo) large SEPs are of immediate concern as they can penetrate the magnetosphere causing widespread electrical disruptions in the regions close to the poles and to the passengers of high-altitude aircraft flying in polar routes. This is an introduction to an interesting topic called Space Weather where I would stress the importance of this field of research highlighting it's beauty and the danger. In addition we present results of our recent statistical analysis on 38 non-interacting CMEs and their associated SEPs during the quadrature configuration of Solar TErrestrial RElations Observatory (STEREO) with respect to the Earth.

The way galaxies stop forming new stars (quenching) is a key aspect of galaxy evolution. This is connected with removal of gas, the fuel of star formation. I will review what we know about the mechanism of the removal of interstellar medium (ISM) from galaxies and how fast this process is. I will then present an alternative way to study the ISM removal by selecting dusty early-type galaxies, for which the decrease of gas and dust can be tracked as a function of age. This led to the first direct measurement of the ISM removal timescale and to the conclusion that the cold ISM is likely removed by feedback from old stellar populations.

According to recent studies, the vast majority of the stars in our Galaxy are orbited by exoplanets. Most of them have been detected around main sequence stars. However, the number of detected exoplanets around subdwarfs or white dwarfs remains very low. This is in spite of the fact that these evolved and compact stars should be the most suitable objects for exoplanetary study. In this talk you will hear about the current status of our investigation on the substellar bodies presence in the proximity of the pulsating blue subdwarfs (sdB), white dwarfs (WD) and short period binary systems containing sdB or WD stars. Our methods of analysis rely on the detection of exoplanetary signals hidden in photometric time series data from the Kepler space telescope, and they are based on natural clocks within the data itself, such as stellar pulsations and eclipse times.

The mechanism behind the Long Secondary Period (LSP) observed in pulsating red giants still remains unknown. I investigate the connection between the Red Giant Branch and Asymptotic Giant Branch evolution and the appearance of the LSP. I use the OGLE-III sample of the Long Period Variables in the Large Magellanic Cloud. I construct the density maps in the period-luminosity as well as color-magnitude planes for the stars showing LSP and compare them to the remaining giants. I also fit the spectral energy distribution to test whether additional source of reddening is present in the LSP stars. I show that the LSP phenomenon is clearly related to a transition between different pulsation period-luminosity sequences. I also show that the overabundance of the stars showing Long Period Variables can be observed around the Tip of the Red Giant Branch, and much more prominently, at the upper end of the Asymptotic Giant Branch. The main over-density region appears to be slightly fainter and redder than the bulk of the Asymptotic Giant Branch. It also seems to correspond to the area of the Hertzsprung-Russell diagram, where stable winds and high mass loss are present. The LSP is likely to be a recurring phenomenon appearing and disappearing in various points of the red giant evolution. The LSP stars appear to be more reddened than other giants, which suggests the intrinsic nature of the reddening, likely related to large dust emission. The analysis seams to confirms the hypothesis about relation between the mass loss due to the presence of strong stellar wind and the appearance of LPS.

The existence of not discovered yet ultra-dense baryonic dark matter came from astrophysicist Edward Witten (Witten, 1984). In his concept the pieces of early Universe containing quarks s did not underwent inflation and could exists currently as one of a kind of dark matter. It was suggested, that due to ultrahigh density such matter can penetrate the Earth (Herrin & Toeplitz, 1996, Rafelski et al., 2012). It was also proposed, that such penetration can left traces in Earth in form of kimberlite pipes (Paszkowski & Mietelski, 2013). The kimberlite pipes are perhaps the most unique geological structures present on Earth. There are narrow tubes having even few meters in diameter but at least several tens of kilometers length. They are filled with ultramafic mantle breccia mixed with crustal xenoliths, connecting the deep mantle with the planet's surface. Almost 6000 such objects were found so far on Earth (Tappe et al., 2018). They are famous due to their diamond content, which is evidence for the direct mantle origin of kimberlite rock. The present state of knowledge cannot propose a widely convincing mechanism to explain how these structures were formed. The most popular ("classical") model try to explain their formation by gas eruption from mantle gas deposits, originating from decomposition of subducted sediments. In our dark matter impact model, the high-energy massive projectile forms a narrow tunnel which is immediately enlarged by explosive degassing of deeper rocks. The empty tunnel is then raidly filled up with pyroclastic material from mantle mixed with some crust rocks fallen from tunnel walls.
One of possible such baryonic dark matter impact was Tunguska event in 1908 (Refelski et al, 2012, Paszkowski & Mietelski 2013, Froggatt & Nielsen, 2015). So far the possible explanation of what happened there was meteoroid of comet impact, "classical" kimberlite (not induced) gas eruption (Kundt, 2001) or even micro black hole Earth chord transition (Jackson & Ryan Jun, 1973). Proposed explanation is based on scenario when impact of condensed ultra- dense object (CUDO) made of baryonic dark matter "seed" surrounded by aggregate of normal matter occurred. During atmospheric passage a fractionation of ordinary matter and dense "seed" happened. The first one produced all effects typical for normal meteoroid impact, whereas the "seed" penetrated Earth chord like micro black hole causing gas eruption and kimberlite-pipe emplacement process, finally the dense "seed" escaped from Earth in North Atlantic area rising to stratosphere hot water vapors plume, what caused famous night air glow observed from Europe in time of Tunguska event. So, this scenario compromise all proposed explanation in one explaining all aspects of Tunguska event.
It was proposed in our model, that during such dark matter object impact the energy was high enough to generate nuclear reactions and therefore they can left some isotopic unusual signature. The experimental part of project is mostly based on search for hard to explain in other models possible existence of traces of non-typical radionuclides. In case of Tunguska area samples search for any activation product will be conducted. In case of old (~100 Ma) kimberlite material search for long lived radionuclides like: U-236 (T_1/2=23.4 Ma), Pu-244 (T_1/2=80.8 Ma), Cm-247 (T_1/2=15.6 Ma) or Sm-146 (T_1/2=64 Ma) is proposed. The strange or unique isotopic signatures for stable isotopes in material from kimberlite pipes are known already.

The tidally tilted pulsators are a new type of oscillating stars in close binary systems. They appear to pulsate principally in one hemisphere because their pulsation axes have been tilted into the orbital plane by the tidal forces exerted by a close companion star. We have so far discovered three of those systems in TESS space photometry data as well as noticed some related cases in the literature. Aside from all pulsators being Delta Scuti stars, and the orbital periods being shorter than two days, all those systems are different in terms of their pulsational behaviour, secondary star and Roche Lobe filling factor. We will present an overview of those stars, as well as our initial results and work in progress.

In some spiral galaxies the so-called 'magnetic arms' have been reported, being interarm areas with significant polarized radio emission that suggests high ordering of the magnetic field. The most prominent example of such a galaxy is NGC6946. The nature of these magnetic features is still under debate. One of the possible explanations is the action of reconnection heating that could convert the energy of the turbulent magnetic field into thermal energy of the surrounding gas, which would result in a higher ordering of the magnetic field and increase in the temperature of the gas. We summarize the analysis of the radio and X-ray emission (measured with XMM-Newton) from NGC6946 and M83 and conclude that we might see hints for such reconnection heating. A similar analysis is on-going for further galaxies that show prominent magnetic arms in their polarized radio intensity maps.

Gravitational waves detected by LIGO and VIRGO are extremely weak and as such they are well described far from sources by linearized general relativity. However, Einstein field equations are highly nonlinear. The exact solutions which correspond to gravitational waves imply effects not predicted by the linear theory. In this talk, I will present the motivation behind our recent research on exact gravitational wave spacetimes. The details of our results will be discussed next week in the second part of the presentation.

The phenomena of standing waves are mostly studied in the context of mechanical or electromagnetic waves. In the context of General Relativity, the issue of how to define standing gravitational waves was addressed by Bondi and later by Stefani. We investigate an expanding universe filled with standing gravitational waves. We study how freely falling particles in this spacetime behave, namely, we investigate the geodesic equation and the geodesic deviation equation. We show that antinodes attract freely falling particles and we trace the velocity memory effect.

During the talk, I will present a catalog of quasars with their corresponding redshifts derived from the photometric Kilo-Degree Survey (KiDS) Data Release 4. We achieved it by training machine learning (ML) models using optical ugri and near-infrared ZYJHKs bands. We define inference subsets from the 45 million objects of the KiDS photometric data limited to 9-band detections, based on a feature space built from magnitudes and their combinations. The model selection and fine-tuning employs two subsets of objects: those randomly selected and the faintest ones, which allows us to properly fit the bias vs. variance trade-off. We test three ML models: Random Forest (RF), XGBoost (XGB) and Artificial Neural Network (ANN). We find that XGB is the most robust and straightforward model for classification, while ANN is the best for combined classification and redshift. The ANN inference results are tested using number counts, Gaia parallaxes and other quasar catalogs external to the training set. Based on these tests, we derive the minimum classification probability for quasar candidates which provides the best purity vs. completeness trade-off. We find 158,000 quasar candidates in the safe inference subset (r < 22), and further 185,000 in the reliable extrapolation regime (22 < r < 23.5). Test-data purity equals 97%, completeness is 94%, the latter dropping by 3% in the extrapolation to data fainter by one magnitude than the training set. The photometric redshifts are derived with ANN and modelled with Gaussian uncertainties. Test-data redshift error (mean and scatter) equals 0.009 +/- 0.12 in the safe subset, and -0.0004 +/- 0.19 in the extrapolation, averaged over redshift range 0.14 < z < 3.63. Our success of the extrapolation challenges the way that models are optimised and applied at the faint data end. The resulting catalog is ready for cosmological and Active Galactic Nucleus (AGN) analysis. We publicly release the catalog at kids.strw.leidenuniv.nl/DR4/quasarcatalog.php.

Pictor A, recognized as the archetypal powerful radio galaxy of the FR II type, is not only one of the brightest radio sources in the sky, but is also particularly prominent in the X-ray domain. In this talk, I will summarize our analysis of all the Chandra X-ray Observatory data available for the Pictor A radio galaxy, consisting of multiple pointings spanning over 15 years and the total exposure time of 464 ks. In particular, the following three main research results discussed during my talk will be: (i) investigating the X-ray structure of the termination shocks of relativistic jets in Pictor A, the so-called "hotspots", by means of detailed image deconvolution and timing analyses; (ii) investigating correlations between the X-ray and radio emission features within the extended lobes of the source; and (iii) an approach to the X-ray spectroscopy of the active nucleus in Pictor A radio galaxy, carried out in a regime of a severe instrumental pile-up.

The X-ray radiation emitted by the accreting matter in active galactic nuclei (AGN), is widely believed to originate close, or even very close to the central super-massive black holes (SMBHs). First, when optical/UV disc photons are inverse-Compton scattered by a corona of hot electrons around the SMBH, the main X-ray continuum emission takes on a power-law shape. Second, a fraction of this radiation is reflected and reprocessed by the absorbing gas and dust located further away from the center. The reprocessing of the X-ray continuum includes photoelectric absorption, followed by fluorescent line emission. Out of all fluorescence features, the iron feature is the most prominent; this is due to the combination of the high relative abundance of iron, and its high fluorescence yield. Moreover, when produced around the innermost orbits of the accretion disks, the iron features may be relativistically broadened and gravitationally redshifted, depending on the disk structure and the black hole spin.

In my research, summarized in this talk, I have analyzed the X-ray radiative output of three radio-loud AGN of various types, focusing, in particular, on their Fe fluorescence emission. The analyzed systems are the broad-line quasar 4C+74.26 with giant large-scale radio morphology, the LINER-type AGN hosted by a post-merger disk galaxy CGCG 292-057, with a multi-component radio morphology reflecting intermittent activity of the central SMBH, and finally the youngest radio galaxies known, 1146+596, hosted by an elliptical NGC 3894 with a low-luminosity active nucleus.

All in all, my research reveals a prevalent fluorescent iron line emission in various types of radio-loud AGN, including both low- and high-luminosity objects. There is a variety in the iron features in the population of jetted AGN, including relativistically broadened lines, ionized lines, and neutral lines with a larger range of equivalent widths. The research I have carried out highlights, in general, the importance of iron fluorescence studies for radio-loud AGN, for which the constraints regarding the innermost structure of AGN, enabled exclusively by the X-ray spectroscopy, can be uniquely complemented by the constraints on the energetics and duty cycle of the systems following from the analysis of their radio (jet) emission.