Lukas Hellström (CAMK, Warsaw)
(CAMK, PAN)
Maciej Wielgus (Max Planck Institute for Radio Astronomy (Bonn, Germany))
In 2017 Event Horizon Telescope (EHT), a global array of radio telescopes, observed the giant supermassive black hole M87* in the center of the M87 galaxy. These observations resulted in the first image of a black hole resolved at the event horizon scale. We have now completed the analysis of the corresponding data, with results on total intensity (2019), linear polarization (2021), and circular polarization (2023). It is a good time to summarize and systematize what we have learned about black holes, accretion disks, and magnetic fields from the EHT observations. Moreover, I will discuss the most recent first EHT results from 2018 observations of M87*, allowing us to study the persistence and variability of the black hole shadow image.
Piotr Gawron (CAMK/Astronet, Warsaw)
Quantum computing is at the same time a fascinating model of computation that uses the fundamental principles of Nature; great engineering challenge; and a promise of calculating the impossible and acquiring unimaginable riches. During the talk we will try to present what quantum computing really means, what it is not, what are hopes related to and what are the challenges in implementation of quantum computing. We will show simultaneously how little is possible to achieve with quantum computers today and how unimaginably marvellous the quantum computers — those tiny universes at our command — are.
Mirosław Giersz (CAMK, Warsaw)
I will very briefly discuss the formation and evolution of multiple populations in globular clusters from the point of view of observation and theory. Then I will present the main scenarios of their formation and discuss their weaknesses. Finally, I will focus on describing the results of simulations carried out with the MOCCA Monte Carlo code and summarize the conclusion resulting from these simulations in the form of a speculative scenario.
Sreekanth Harikumar (National Center for Nuclear Research, Warsaw)
The first direct detection of gravitational waves by LIGO collaboration has opened a new era of Gravitational Wave astronomy. The bending of light by massive objects is a prediction of General Relativity (GR) and this phenomenon known as gravitational lensing has now become an indispensable tool in astrophysics. Therefore, in this era of astronomy, the next most anticipated event is the detection of gravitational waves lensed by massive sources along the line of sight. The lensed gravitational waves has many applications such as detection of Intermediate Mass BlackHoles (IMBH), Primordial Black Holes, precision cosmology etc. Another emerging avenue is the test of GR, in this talk I will discuss the predictions of f(R) and Palatini f(R) in the context of lensing of gravitational waves.
Young astronomers meeting at CAMK (CAMK, Warsaw)
Sumanta Kumar Sahoo (CAMK, Warsaw)
Hot subdwarf stars are extreme horizontal branch stars, consisting of a convective helium-burning core, helium shell, and a thin (in mass) hydrogen envelope. A few of these subdwarfs pulsate, which opens the window to study these stars using asteroseismology. The majority of such pulsating stars detected are B-type stars (sdBV). From the TESS mission, we have detected a few tens of rich gravity mode sdBVs by analyzing their short cadence (SC) light curves and identified their pulsation mode geometries. Apart from the SC data, we also extracted light curves from TESS full frame images for the targets not observed in SC mode and analyzed them to detect pulsations. I will be talking about these pulsating subdwarf stars and our study to understand their pulsation properties.
Jonas Pereira (Núcleo de Astrofísica e Cosmologia & Departamento de Física, Universidade Federal do Espírito Santo, Vitória, Brasil and CAMK, W)
Binary coalescences are known sources of gravitational waves (GWs) and they encompass combinations of black holes (BHs) and neutron stars (NSs). I’ll show that when BHs are embedded in magnetic fields (B’s) larger than approximately e10 G, charged particles colliding around their event horizons can easily have ultrahigh energies (≳ e18 eV) and become more likely to escape. Such B-embedding and high-energy particles can take place in BH-NS binaries, or even in BH-BH binaries with one of the BHs being charged (with charge-to-mass ratios as small as e-5, which do not change GW waveforms) and having a residual accretion disk. The number of collisions leading to ultrahigh energy particles is estimated to range from a few up to millions before the merger of binary compact systems. Thus, binary coalescences may also be efficient sources of ultrahigh energy cosmic rays (UHECRs) and constraints to NS/BH parameters would be possible if UHECRs are detected along with GWs.
The presentation will be based on recent PRL work:
Binary Coalescences as Sources of Ultrahigh-Energy Cosmic Rays
Jonas P. Pereira, Carlos H. Coimbra-Araújo, Rita C. dos Anjos, and Jaziel G. Coelho
Phys. Rev. Lett. 132, 091401 – Published 27 February 2024
Lucas Tonetto (Dipartimento di Fisica, “Sapienza” University of Rome, Italy)
In different astrophysical systems involving neutron stars, such as mergers or newly born stars, a reliable model of a finite-temperature equation of state is needed. Temperature has implications in equilibrium and dynamical phenomena, therefore a fully consistent framework should be able to take into account thermal effects in single-nucleon properties alongside yielding accurate results for average thermodynamic quantities. In this talk, I present the results of employing a recently developed effective interaction based on the Correlated Basis Functions theory, being able to account for nuclear correlations and two- and three-nucleon potentials. After discussing the properties of its generalisation to nonzero temperature, we apply it in the calculation of the neutrino mean free path and emissivity. In the latter, we study how in-medium effects alter the results by using effective weak transition operators.
Krzysztof Nalewajko (CAMK, Warsaw)
Black holes (BH) acquire relativistic magnetospheres by accreting magnetized gas. Once they collect significant magnetic flux across the horizon, aided by the spin they can drive powerful relativistic jets by the Blandford-Znajek mechanism. Large enough BH magnetic flux backreacts on the accretion flow, which has been described in terms of arresting or choking. Magnetic flux eruptions have been identified as the mechanism of BH magnetic flux saturation. These eruptions can potentially dissipate a large fraction of magnetic energy in the BH magnetosphere by means of relativistic magnetic reconnection, accelerating particles and producing flares of non-thermal radiation. We analyze the results of 3D general-relativistic ideal magnetohydrodynamic (GRMHD) numerical simulations of accretion flows onto magnetically saturated Kerr BHs, focusing on the initiation of magnetic flux eruptions.
Radek Poleski (Astronomical Observatory Warsaw University)
There are four main methods of finding exoplanets: transits, radial velocity, microlensing, and direct imaging. Each of these methods comes with its own biases and limitations. The microlensing technique allows finding planets on orbits similar to the ones in the Solar System as well as free-floating planets (i.e., not bound to any star) of low mass. I'll present how the microlensing method works and what are the current constraints on the population of bound and free-floating planets. I'll also present prospects for a microlensing survey that will use the Nancy Grace Roman Space Telescope - a NASA flagship mission currently built and scheduled to be launched in 3 years.
Fatemeh Kayanikhoo (CAMK, PAN, Warsaw)
In our simulations accreting magnetized neutron stars are considered to be potential pulsating ultraluminous X-ray sources. Due to the neutron star's magnetic field, the emission is beamed, resulting in apparent luminosity that exceeds the Eddington luminosity expected from stellar mass objects. In my research, I investigate the impact of the surface magnetic field of a neutron star on the photosphere and luminosity by using GRRMHD simulations. Our study shows that strong magnetic fields truncate the disk and quench the outflows, which lowers the luminosity. Moreover, our simulations demonstrate that the beaming emission decreases as the magnetic field increases.
Grégoire Marcel (CAMK, Warsaw)
The hysteresis behavior of X-ray binaries during their outbursts remains a mystery. In this work, we developed a paradigm where the disk material accretes in two possible, mutually exclusive, ways (Ferreira et al. 2006). In the usual alpha-disk mode (SAD, Shakura & Sunayev 1973), the dominant local torque is due to a radial transport of the disk angular momentum. In the jet-emitting disk mode (JED), magnetically-driven jets carry away mass, energy, and angular momentum vertically. Within this framework, the transition from one mode to another is related to the magnetic field distribution, an unknown. We have shown that typical hard states of X-ray binaries can be reproduced up to unprecedented X-ray luminosities in this paradigm (Marcel et al. 2018a,b,2019). Direct spectral fits have since been performed on an AGN (Ursini et al,. 2020), as well as two X-ray binaries (Marino et al. 2021, Barnier et al. 2022), showing striking dynamical similarities between the two accretion flow structures despite the factor > 10^6 in mass. Moreover, we have addressed the production of low frequency quasi-periodic oscillations during the outbursts (Marcel et al. 2020, Marcel & Neilsen 2021), the radiative efficiency of the accretion flow and the associated radio--X-ray correlation (Marcel et al. 2022), as well as the production of winds (Petrucci et al. 2021), the latest results from IXPE (Zhang et al., in prep.), and the timing properties of X-ray binaries (Malzac & Marcel, to be submitted).
Andrzej Sołtan (CAMK, Warsaw)
The galaxy autocorrelation function (ACF) is constructed using the galaxies selected from the DR12 of the SDSS. The ACF amplitude increase at separa- tions expected to those generated by the Baryon Acoustic Oscillations (BAO) is clearly detected. We study the dependence of this correlation signal on the angle between the line of sight and vectors defined by galaxy pairs. Using the Alcock-Paczyński test we estimate acceptable amplitudes of the matter and cosmological constant density parameters, Ωm and ΩΛ. Only flat cosmological models are considered, e.g. Ωm + ΩΛ = 1. We found that in the local Universe 0.25 . Ωm . 0.45, what is in agreement with the results based the CMB me- asurements. Strong stoochastic variations of local galaxy concentrations generate substantial scatter of the ACF signal unrelated to the BAO, what significantly degrades the accuracy of the present estimates.
Solen Balman (Department of Astronomy and Space Sciences, Istanbul University)
Cataclysmic Variables (CVs) and related systems (e.g., AM CVn, Symbiotics) are compact systems with white dwarf (WD) primaries referred as accreting white dwarfs (AWDs). They are excellent laboratories to study astrophysical plasmas, accretion flows and disks, gas dynamics, outflows, and transient outbursts. Broadband noise and its variations in accretion flows have been a diagnostic tool for understanding the structure of accretion disks together with accretion history and state changes. CVs demonstrate band limited noise (mainly 1-6 mHz) in the optical, UV and X-ray energy bands, which can be adequately explained in the framework of the model of propagating fluctuations yielding break frequencies. I will discuss broadband noise structure in CVs with a broader sense including some different nonmagnetic AWDs elaborating on similarities along with spectral characteristics. The spectral and/or broadband noise studies show that advective hot flow structure (ADAF-like) resides inside nonmagnetic CV disks mainly detected in the X-ray regime (Balman 2020, Balman et al. 2022 and references therein) indicating other characteristics like outflows in the X-rays and warm absorber effects.
Ewa L. Łokas (CAMK, Warsaw)
Galactic bars are generally believed to form via disk instability. There is however another channel for the formation of these structures: by tidal effects. I will review the process of formation and evolution as well as describe the properties of bars induced in galaxies as a result of tidal interactions between them and a larger or equal-mass companion. I will start by describing the results of controlled simulations of dwarf galaxies orbiting the Milky Way and then move to normal-size galaxies interacting during flybys or orbiting galaxy clusters. Then I will place this scenario in the cosmological context and discuss tidally induced bars in galaxies formed in the simulations of the IllustrisTNG project, including a recently identified analog of the Sagittarius dwarf.
Adi Nusser (Technion, Haifa)
The equivalence principle ensures that galaxy motions are unbiased with respect to the velocity field of the underlying mass density field, making galaxy peculiar motions our only direct probe of the three-dimensional distribution of dark matter. However, analyzing peculiar velocity data is challenging due to large errors that increase with distance and the sparse spatial coverage of the data. The talk will discuss methods for constraining cosmology using observed galaxy motions, including traditional approaches and new AI/ML-based methods.
Anna Cetera-Włodarczyk and Jarosław Włodarczyk (Institute of English Studies, Warsaw University (ACW), Institute for the History of Science PAN (AW))
London at the turn of the 17th century is one of the most fascinating places to investigate the reception of the new astronomy propelled by the Copernican revolution and astronomical observations. William Shakespeare’s imagery has been typically placed within the geocentric model of the universe, firmly anchored in the medieval paradigm, denying any impact of the new models of cosmos. But was he really so ignorant of the ongoing revolution? The much overused dichotomy between geo- vs. heliocentrism does not give justice to the complex intellectual climate of the age. Drawing on the history of astronomy and literary linguistic analysis, we argue that Shakespeare’s references to the unsphered and disorbed planets and stars are better understood when viewed in the light of the disputes of the times, the decline of the concept of the celestial orbs in particular. Hence we shall rehearse the 16 th century astronomy to read Shakespeare’s metaphors.
Anna Barnacka
Dr. hab. Anna Barnacka defended her PhD at CAMK PAN in parallel with a French PhD given at the same time (under the agreement of a double PhD program between Poland and France). She got her postdoc position at Harvard, and shortly after she was awarded the prestigious Einstein fellowship. But then, her career took a turn into medicine and technologies. She is an owner of MindMics start-up, in which she developed a new technology for monitoring heart rate via headphones into the phone. Let's meet her and take a look at her fascinating career path.
Nafisa Aftab (Raman Research Institute)
X-ray reprocessing serves as a vital diagnostic tool for gaining insights into the environments of X-ray binary systems. However, the study of X-ray reprocessing encounters challenges arising from the blending of intense primary radiation from the compact star with the reprocessed radiation from the surrounding. Eclipsing X-ray binaries offer a unique opportunity to investigate pure reprocessed X-rays, as the companion star effectively shields the intense primary X-rays during eclipse. We carried out comprehensive studies of X-ray reprocessing in several eclipsing High Mass X-ray Binary (HMXB) and Low Mass X-ray Binary (LMXB) systems by comparing their X-ray spectra during and outside of eclipse using XMM-Newton. We found ample diversity in the X-ray reprocessing characteristics in HMXBs, which implies significantly dynamic wind structure surrounding the compact objects in HMXBs. Even in the same source at different epochs, the variation is quite large. Significant differences observed in X-ray reprocessing characteristics in LMXBs too, despite all being dipping and eclipsing sources, suggest large dependencies of X-ray reprocessing in LMXBs on the inclination angle, scale height of the accretion disk, relative size of the accretion disk with respect to the companion, binary separation and many other known and unknown factors. Overall the studies deepen our understanding of the intricate interplay between X-ray reprocessing and the diverse mechanisms within X-ray binary systems. In these studies we have also observed some unexpected behaviours of the X-ray binaries and the exact reason of which is not yet clear. We anticipate that discussion with you all will illuminate these unexpected behaviors in X-ray binaries and inspire numerous new avenues for future research on these intriguing systems.
Wojciech Hellwing (Center for the Theoretical Physics, PAN, Warsaw)
Modern cosmology thanks to evergrowing precision and volume of astronomical data has become high precision science. Yet this amazing growth has come at a price. The precise observations has revealed a number of strange anomalies between the model and the data. These are commonly called "LCDM tensions" and include H0 tension, S8 tension, early galaxies problem and so on. In my talk, using some examples from my own research, I will show how such anomalies can partially and potentially be obscured by strange systematic and hidden degeneracies based on physics that wasn't even considered before the era of precision cosmology. I will also point towards possible remedies that can help us break this degeneracies and give us better understanding of the data and the cosmos.
Weronika Narloch (CAMK, Warsaw)
Since its discovery by Henrietta Swan Leavitt, the period-luminosity relation (also known as the Leavitt Law) for pulsating stars has been a useful tool for measuring cosmic distances. Over time, it has become a crucial rung of the so-called extragalactic distance ladder, important for measuring the famous Hubble constant, which can be interpreted as the rate of expansion of the universe. For this reason, period-luminosity relationships have become the object of interest for the Araucaria group. In this talk, I would like to present our recent efforts to calibrate these relations for different types of pulsating stars in our Galaxy, in the Sloan bands.
Amit Kumar Mandal (Center for Theoretical Physics, Polish Academy of Science, Warsaw)
This talk will focus on understanding the innermost structure of Active Galactic Nuclei (AGNs), which cannot be resolved by any existing imaging techniques, through multi-wavelength observations. The flux variability of AGN serves as a powerful tool to map the extent of both the dusty torus and the broad line region (BLR) surrounding the central supermassive black hole (SMBH). Reverberation mapping (RM) is a key technique that enables estimates of SMBH mass (M_BH) across a range of redshifts. RM relies on measuring the time delay between variations in the continuum emission and the corresponding response from the line-emitting gas and the reprocessed torus emission. In this talk, I will focus on constraining the torus size-luminosity relation in AGNs by utilizing optical data from ground-based surveys such as ASAS-SN, CRTS, PTF, and ZTF, along with infrared data from the Wide-field Infrared Survey Explorer (WISE) in the W1 and W2 bands. Additionally, I will briefly discuss accretion disk continuum reverberation mapping, which helps to determine the size of the continuum-emitting region in the accretion disk and its correlation with key AGN parameters, including luminosity and accretion rate.
Knut Olsen (NOIRLab, Arizona)
I will present an overview of the Vera C. Rubin Observatory project and its planned Legacy Survey of Space and Time (LSST), scheduled to start in 2025. The overview will include LSST’s science goals, the status of the construction project, the plans for operations (including the role of the Rubin In-Kind program), and the planned observing strategy.
Thibault Boulet (Institute of Astrophysics and Space Sciences, University of Porto, Portugal)
Understanding the Milky Way's formation and evolution requires precise stellar age determination across its components. Recent advances in asteroseismology, spectroscopy, stellar modeling, and machine learning, along with all-sky surveys, have provided reliable stellar age estimates. We aim to furnish accurate age assessments for the Main Red Star Sample within the APOGEE DR17 catalogue. Leveraging asteroseismic age constraints, we employ machine learning to achieve this goal. We explore optimal non-asteroseismic stellar parameters, including Teff, L, [C/N], [Mg/Ce], [α/Fe], U(LSR), and 'Z' vertical height from the Galactic plane, to predict ages via categorical gradient boost decision trees. Our model, trained on merged samples from TESS and APOKASC-2 catalogs, achieves a median fractional age error of 20.8%, with a relative difference between the learning curves of 4.77%. For stars older than 3 Gyr, the error ranges from 7% to 23%; for those between 1 and 3 Gyr, it is 26% to 28%; and for stars younger than 1 Gyr, it is 43%. Applied to 125,445 stars, our analysis confirms the flaring of the young Galactic disc and reveals an age gradient among the youngest Galactic plane stars. We also identify two groups of metal-poor ([Fe/H] < -1 dex) and young (Age < 2 Gyr) stars exhibiting peculiar chemical abundances and halo kinematics. One of these groups is likely a remnant of the third gas infall episode that started around 2.7 Gyr ago.
Henryka Netzel (CAMK, PAN, Warsaw)
Our perception of RR Lyrae stars and classical Cepheids have changed dramatically in recent years. Precise photometric observations from ground-based surveys and space missions have revealed a plethora of additional periodicities and modulation phenomena that occur alongside the dominant simple radial pulsations. Some of these phenomena have been explained with satisfactory hypotheses, while the nature of others remains a mystery. Although most discoveries come from photometric observations of RR Lyrae stars and classical Cepheids, the most recent findings originate from spectroscopic time-series observations of classical Cepheids. I will summarize the latest advances on the pulsation properties of classical pulsators and present the newest developments in the field, focusing on spectroscopic observations.
Tomasz Krajewski (CAMK, Warsaw)
Even though, naked singularities are perceived by many scientists only as strictly academic curiosities, solutions of the Einstein equation representing them are not hard to obtain. The well-known Reissner-Nordström (RN) metric is an example that can model black holes as well as naked singularities. It turns out that the RN metric is not only the solution of the Einstein equation coupled to the Maxwell electrodynamics, as it was obtained for the first time more than a century ago, but is also the solution in certain modified theories of gravity. In this talk we will go beyond well-studied accretion onto black holes described by the Kerr metric and investigate the analogous process in the background of the RN one. We will consider both regimes, i.e. when the charge parameter Q is smaller than the mass M of the black hole or when it is greater than M and the metric describes the naked singularity. We will discover new, exciting phenomena like repulsive gravity, levitating atmospheres and much more. Our findings may have applications to astrophysics of the active galactic nuclei (AGNs) with their powerful jets and outflows
Shilpa Sarkar (Harish-Chandra Research Institute (HRI), India)
Accretion is one of the most efficient processes by which the gravitational potential energy of matter can be converted into radiation. This phenomenon provides us with an explanation of the huge amount of energy liberated and high luminosities observed in Active Galactic Nuclei, X-ray binaries, etc. Therefore, modelling of these accretion flows is necessary to understand the underlying physical processes present in these systems. The soup of protons and electrons in these ionised flows are bound together by weak Coulomb force. Additionally, in most of the astrophysical cases, the infall timescales are much shorter. This makes the species settle down into two different temperature distributions, hence, the name two- temperature flows. However, this theory suffers from a serious problem of degeneracy. Compared to one- temperature flows, there is one more variable in the two-temperature system -- the extra temperature. However, there is no increase in the number of equations of motion. Thus, no unique solution exists, for a given set of constants of motion; or in other words, the system is degenerate! Different values of Tp/Te ratio supplied at any boundary, would generate different kinds of solutions with drastically different topologies as well as spectra. In addition, there is no known principle dictated by plasma physics which may constrain the relation between these two-temperatures. This degeneracy is irrespective of the type of the central object and is generic to two-temperature flows. We propose for the first time, an entropy maximisation formulation using the first principles. Using this methodology, we were able to constrain degeneracy and a unique solution with maximum entropy was selected following the second law of thermodynamics. Thereafter, we analysed the spectrum of these unique solutions for different accreting systems like black holes and neutron stars.
Piotr Wielgórski (CAMK PAN, Warsaw)
Radially pulsating stars, like Cepheids (Classical, Type II) and RR Lyrae are widely used as precise distance indicators thanks to their period-luminosity relations which serve as a standard candle. However, there is another, semi-geometrical method which can be used to derive distances of such stars, known as the Baade-Wesselink or parallax-of-pulsation technique. In this method, change of the angular diameter of the star, which is calculated from photometric or interferometric measurements, is compared to the physical radius displacement obtained from integrating the pulsational velocity curve (velocity of the atmosphere of the star during pulsations). Pulsational velocity can be obtained from radial velocity measured from doppler shift of absorption lines in spectra once the so-called projection factor (p-factor) is known. The value of this parameter is primarily the result of the geometrical projection of the pulsational velocity of different parts of the stellar disk onto the line of sight, but factors like limb darkening, velocity gradient in the atmosphere etc. modify the value of p-factor. Precision of the Baade-Wesselink method is currently limited to ~5-10% due to poor knowledge of this parameter. During my talk I will present the efforts of the Araucaria group in calibrating the projection factor.
Oliver Porth (University of Amsterdam)
The time-variable (in particular pulsed-) emission from black holes and neutron stars holds key information on the nature of curved spacetime and ultra dense nuclear matter. However, due to the complex plasma dynamics at play, the interpretation of the observed signals is difficult. I will present some of our recent work on modeling general relativistic magnetohydrodynamic processes around black holes and accreting neutron stars. I will first discuss the dynamics of strongly perturbed black hole magnetospheres as they can occur for example during binary neutron star merger events. The simulations have revealed an intriguing rapid alignment of the magnetic moment and black hole spin which can uniquely imprint the high energy emission of the current sheet. I will further discuss the dynamics of multipolar black hole magnetospheres (Selvi et al. in prep). Switching gears, I will then discuss our recent 3D simulations of accreting neutron stars with oblique magnetospheres, focusing on the questions of jet formation and pulsed emission. The obtained X-ray pulse profiles are consistent in amplitude and harmonic content with the observations of AMXPs, however they also exhibit significant and rapid variability in hotspot temperature and shape due to the turbulent accretion flow.
Arkadiusz Orłowski (Department of Artificial Intelligence, Institute of Information Technology, SGGW, Warsaw)
