Wednesday Colloquium


"Non-Riemannian signatures and nature of gravity"

Krzysztof Bolejko (University of Tasmania, Australia)

Einstein's theory of gravity, General Relativity was built on the theory of Special Relativity. This generalisation required utilising the full generality of the Riemannian geometry. Many of the present-day cosmological tests of GR are still based on the assumption of the Riemannian geometry. However, to fully study and test various extensions of GR one is also required to move beyond the Riemannian geometry. In my talk I will focuses on light propagation and discuss what signatures in cosmological observational data could point to non-Riemannian effects. I will focus on "litmus test" type signatures that are only present in non-Riemannian geometries, thus providing a model-independent way of testing GR on cosmological scales. This talk will not be a comprehensive review of the issue - it will only focus on the distance and redshift relations. I will discuss observational constraints and talk how future surveys could provide a better insight into the underlying geometry of our Universe.


"Simulating ULXs: super-Eddington accretion onto magnetized neutron stars"

David Abarca (CAMK, Warsaw)

Observations of ultraluminous X-ray sources (ULXs) paired with coherent pulsations have shown that accreting neutron stars are capable of emitting super-Eddington emission. We run general relativistic radiation magnetohydrodynamic simulations of super-Eddington accretion onto magnetized and non-magnetized neutron stars. We show how the combination of an approximately ten billion Gauss stellar magnetic field, the hard surface of the neutron star crust, and collimation from the outflowing gas produce apparent luminosities in excess of 200 times the Eddington limit which is well in the range of observed neutron star ULXs


"Gravitational Lensing in Simulated Images of Black Holes"

Zachary Gelles (Harvard University)

In 2019, the Event Horizon Telescope published the first image of a black hole, paving the way for future efforts to improve our understanding of emission around compact objects. However, many of the most prominent and unexpected effects of black holes on their images are only visible at extremely fine resolutions. To analyze these features, I will describe an approach to adaptive ray-tracing that allows us to efficiently generate high-resolution images of black holes by concentrating rays near sharp features of the image. I will present examples that provide key insights into the turbulent accretion flow and photon ring. In addition to the imprint of the spacetime via gravitational lensing of the total intensity, black holes also impart distinctive features on polarized emission. I will describe efforts to understand polarimetric images of black holes using simplified, semianalytic models of synchrotron emission near black holes, and I will discuss the effects of spin, magnetic field, and inclination angle on the observed polarization. Together, these tools provide insight into the role that black hole imaging might play in understanding the supermassive black holes at the centers of galaxies. I will specifically make comparisons to previous imaging efforts of the Galactic Center supermassive black hole, Sgr A*, and I will discuss the role of these tools in enabling future endeavors in Space VLBI.

due to the time difference the talk will start at 3:15 pm Warsaw time.


"Heat, work and temperature in special relativity"

Lorenzo Gavassino (CAMK, Warsaw)

Heat, work and temperature are probably some of the most elusive concepts of physics. Although we all seem to agree on the intuitive concept underlying these thermodynamic entities, their fundamental meaning in a relativistic context seems to be still under discussion. A fully covariant formulation of the laws of thermodynamics requires that we first put an end to these controversies.


"Exploration of faint parts of bright galaxies in the MATLAS survey"

Michal Bílek (Observatoire astronomique de Strasbourg)

The purpose of this talk will be to introduce myself and present our latest work on the MATLAS survey. MATLAS took very deep optical images of around 200 nearly elliptical and lenticular galaxies to explore very faint structures in the galaxies or their vicinity. Most importantly, the images captured tidal features, the remnants of past galaxy interactions. This will help us to address the role of mergers in the assembly of our galaxies.


"Radio View of Black Holes Shadows"

Monika Mościbrodzka (Radboud University, The Netherlands)

In the final lecture I will overview the black hole imaging using the Event Horizon Telescope. The lecture will discuss recent improvements of the telescope and it’s capability to test the Einstein Theory of Gravity and theory of accretion disks in the future.


"Dwarf Galaxies and the Black Hole Scaling Relations"

Andrew King (Department of Physics and Astronomy, University of Leicester)

The masses of supermassive black holes correlate tightly with properties of their host galaxies. One theory of these scaling relations ascribes them to feedback from black hole accretion, while a completely different picture argues that they arise purely statistically as galaxies and their central black holes are assembled by repeated mergers. Recent observations extend one of these scalings (the M - sigma relation) to dwarf galaxies. I will argue that this allows a clear decision between the two alternative theories of the scaling relations.


"Cosmology and measurements of anisotropy of the cosmic microwave background; Satellite mission Planck – the beginning of the end, or the end of the beginning …"

Krzysztof Górski (Jet Propulsion Laboratory, Pasadena, CA)

After over five years in flight, and the follow on period of science analysis, the satellite CMB mission Planck has been recently completed. I will present personal reminiscences of this remarkably successful effort, address the impact of its science results on modern cosmology, and comment on the future of space exploration of the cosmic microwave background.

Due to the time difference between Warsaw and Pasadena, the seminar will be held at 17:15 (local time in Warsaw). Informal gathering will start at 16:45.


"Episodic outflows from SANE discs"

Miljenko Cemeljic (CAMK, Warsaw)

Episodic outflows from SANE discs Abstract: We investigate the episodic ejection of plasmoids from a hot accretion flow around a black hole. Based on full 3D numerical simulations with General Relativistic MHD code Athena++, described is formation and emergence of the flux ropes and their ejection into the disk corona. Loops of magnetic field form flux ropes, similar to the coronal mass ejections from the Sun. Material captured into such ropes is pushed outwards into corona in periodically repeating ejections. We find that reconnection layers below the flux ropes emerge with the same periodicity from the disk in our simulations as the flux ropes. Above the rope, another reconnection layer forms, which helps the launching into the corona. Application of our results to the case of Sgr A* gives the period of ejections of 6 hours, which matches the time-scale of the observed periodic flares.


"Constraining the geometry of the accretion flow in black hole X-ray binaries"

Marta Dziełak (CAMK, Warsaw)


"How personalised is our immune repertoire?"

Aleksandra Walczak (Laboratoire de Physique, Ecole Normale Supérieure)

Immune repertoires provide a unique fingerprint reflecting the immune history of individuals, with potential applications in precision medicine. Can this information be used to identify a person uniquely? If it really is a personalised medical record, can it inform us about the outcomes of a COVID-19 infection? I will show how statistical analysis of immune repertoires can answer these questions.


"Probing elastic quark phases in hybrid stars"

Jonas Periera (CAMK, Warsaw)

In this talk I will discuss some imprints of elastic quark phases on the stability of hybrid stars and possible ways to probe them with current and future electromagnetic missions such as NICER, eXTP and ATHENA.


"Simulating galaxies at high resolution in their cosmological context with NewHorizon: methods and some key results on galaxy properties and their morphology"

Yohan Dubois (Institut d'astrophysique de Paris)

Hydrodynamical cosmological simulations are increasing their level of realism by considering more physical processes, having more resolution or larger statistics. However, one usually has to either sacrifice the statistical power of such simulations or the resolution reach within galaxies. I will introduce the NewHorizon project where a zoom-in region of∼(16 Mpc)3, larger than a standard zoom-in region around a single halo, embedded in a larger box is simulated at high resolution. A resolution of up to 34 pc, typical of individual zoom-in state-of-the-art resimulated halos is reached within galaxies, allowing the simulation to capture the multi-phase nature of the interstellar medium and the clumpy nature of the star formation process in galaxies. I will present and discuss several key fundamental properties of galaxies and of their black holes. Due to its exquisite spatial resolution, NewHorizon captures the inefficient process of star formation in galaxies, which evolve over time from being more turbulent, gas-rich and star-bursting at high redshift. These high redshift galaxies are also more compact, and are more elliptical, disturbed and clumpier until the level of internal gas turbulence decays enough to allow for the formation of stable rotating discs. I will show the origin and persistence of the thin and thick disc components, and explain why the settling of discs ``magically’’ occurs at around a stellar mass of 1e10 Msun.


"Quantum Gravity is Coming to Town"

Marek Abramowicz (CAMK, Warsaw)


"Massive black holes in the cosmos"

Marta Volonteri (Institut d'Astrophysique de Paris)

Massive black holes weighing from a few thousands to tens of billions of solar masses inhabit the centers of today’s galaxies, including our own Milky Way. Massive black holes also shone as quasars in the past, with the earliest detected a mere one billion years after the Big Bang. Massive black holes during their cosmic evolution interact with diverse environments, starting from messy and rapidly evolving galaxies at high redshift to quiescent galaxies today. I will discuss how these changing environments affect the growth of massive black holes and the formation of massive black hole binaries.


"X-ray spectral and timing studies of ultraluminous X-ray sources."

SAMARESH MONDAL (সমরেশ) (CAMK, Warsaw)

Ultraluminous X-ray sources (ULXs) are off-center point sources with assumed isotropic X-ray luminosity above 10^39 erg/s. Now it is commonly considered that most ULXs have a stellar-mass BH or a NS after the discoveries of several pulsating ULXs. Therefore the luminosity indicates accretion above the Eddington limit. We find various observational signatures of super-Eddington accretion imprinted onto the X-ray observations. In my talk, I will briefly discuss the X-ray spectral and timing properties of these sources and compare them with Galactic X-ray binaries or AGNs.


"High-Amplitude Delta Scuti stars"

Henryka Netzel (CAMK, Warsaw)

High-Amplitude Delta Scuti stars (HADS) is a subgroup of Delta Scuti stars which is characterized by high-amplitude pulsations, typically in radial modes. I studied Delta Scuti stars from the Galactic bulge using the OGLE photometry and selected candidates for HADS pulsating in multiple radial modes. I performed seismic modeling of these selected multi-mode HADS in order to constrain their physical parameters. I will show results of the search for HADS among Delta Scuti stars in the Galactic bulge, their inferred physical parameters based on theoretical models and their properties.


"A shoebox-sized simulator of the antique Cosmos: The ancient Greek Antikythera Mechanism"

Dietrich Baade (ESO Garching)

In 1901, the heavily corroded remains of a strange object were found in an ancient shipwreck. The details of its inner workings remained enigmatic for a century. X-ray tomography obtained a century later and masterly reverse engineering led to a comprehensive reconstruction of its functionality. The result reveals that the mechanism incorporated all Babylonian and Greek astronomical knowledge of its time with an amazing precision. It is the first time machine and analog computer. Its mechanical realization is the work of a genius. The congenial combination of scientific and technical brilliance makes the Antikythera mechanism the most remarkable scientific-technical project of all times. The talk will give an overview of the astonishing diversity of functions and how it was finally possible to decipher them.


"Kinetic simulations of particle acceleration mechanism at relativistically magnetized jets"

José Ortuño-Macías (CAMK, Warsaw)

Blazar emission present spectra with extreme broadness and power-law appearance, which are signatures of an efficient non-thermal particle acceleration process. It is also characterized by strong variability on timescales ranging from decades to minutes. Relativistic magnetic reconnection has been often proposed as the particle acceleration mechanism due to its high efficiency at highly magnetized plasma; where the generated plasmoids, magnetic islands enclosing energetic particles, are the emission sources. Local inversions of the magnetic field lines are required for magnetic reconnection to occur. They may be caused by internal jet instabilities, which recently have been shown to be able to accelerate particles by means of large-scale induced electric field. I will present the results of kinetic numerical simulations for two particle acceleration mechanisms for relativistically magnetized electron-positron plasma: steady state relativistic magnetic reconnection with efficient synchrotron cooling and current-driven instabilities in cylindrical magnetized jets.


"Genetically modified man"

Ewa Bartnik (Warsaw University)

Genetically modified humans can be found not only in books (Brave New World) and movies (GAATACA), but also there are 3 genetically modified girls in China, who were supposed to become resistant to AIDS, and somewhere there is a boy whose mitochondria do not come from his mother but from a donor. Jennifer Doudna and Emmanuelle Charpentier received the Nobel prize in chemistry in 2020 for the CRISPR-Cas9 technique, which makes genetic modifications possible. But what does this mean for us - what can CRISPR-Cas9 be used for, and for what has it already been used?


"The Rosetta-stone cluster M67 and the Sun"

Andreas Korn (Uppsala University, Sweden)

I report on 10+ plus year of work we have put into understanding the detailed chemical composition of the solar-age, solar-metallicity open cluster M67. Because of its near-solar age and metallicity, this cluster lets us address questions related to the Solar-system's early chemical evolution which seems to have led to a Sun relatively rich in volatile and poor in refractory elements. The physical reason for this chemical oddity in unknown at present, but may very well be connected to (giant) planet formation. This work on M67 thus brings together planetary, stellar and Galactic research in a unique and highly interesting way.


"Jets in microquasars"

Andrzej Zdziarski (CAMK, Warsaw)

I will review our current knowledge about three well-studied jets in X-ray binaries, MAXI J1820+070, Cyg X-1, and Cyg X-3. The first two accrete from their donors onto black holes, while this is likely but not certain in Cyg X-3. Thanks to an extensive multiwavelength campaign during the recent outburst of MAXI J1820+070, the structure of its compact jet emitting in radio to optical frequencies is now very well understood. The relatively long time lags measured between various radio and sub-mm frequencies prove that emission is formed at distances several orders of magnitude higher than the gravitational radius. We determine the jet opening angle, the location of the onset of the emission, the magnetic field strength and the electron distribution, and put constraints on the bulk Lorentz factor, the content of electron-positron pairs and the jet power. Then, I will compare those jet parameters with those in Cyg X-1 and Cyg X-3, both of which emit also high-energy gamma rays.


"Glitches: The restless life of a dead star"

Marco Antonelli (CAMK, Warsaw)

Gamers may think to have witnessed some hilarious and weird glitches, but this is nothing compared to what a pulsar can do. Pulsars are famous for being "natural clocks", but some of them display a "restless" behaviour: their rotational evolution is punctuated by sudden hiccups, known as glitches. The origin of glitches is debated, but there is an elegant analogy with the noisy motion of flux-tubes in superconductors: glitches can be explained by transitions in the rate with which vorticity is expelled from the internal layers of a neutron star. Spin in peace, little pulsar.


"Gravitational wave pulsars: the path from theory to observations"

Bryn Haskell (CAMK, Warsaw)


"Physics without experiment and cosmology with no observations?"

Stanisław Mrówczyński (Uniwersytet im. Jana Kochanowskiego and National Ceter of Nuclear Research)

In contemporary physics there emerged theories which cannot be tested experimentally due to either technological or truly fundamental limitations. The quantum gravity belongs to the first category while the theory of multiverse to the second one. One asks about a status of such theories, whether experimental verification can be replaced by another criteria. The whole problem is presented and discussed.


"Beam geometry for pulse modulation in radio pulsars"

Jarosław Dyks (CAMK, Toruń)

Radio pulsations of pulsars are modulated in a variety of ways, and the modulation patterns look truly enigmatic or striking. I will describe a recently proposed radio beam geometry that is capable of producing the main types of the observed behaviour.


"Dancing discs: Lense-Thirring precession and rapid variability > in truncated accretion flows"

Deepika Bollimpalli (Max Planck Institute, Garching)

Many accreting black holes and neutron stars exhibit rapid variability > in their X-ray light curves termed as quasi-periodic oscillations > (QPOs). The most common are the low-frequency (< 10 Hz), type-C QPOs > typically observed during the low/hard state and are thought to > originate from the Lense-Thirring precession of a hot, geometrically > thick accretion flow that is misaligned with respect to the black hole > spin axis. However, it is not yet clear how the coupling between the > outer geometrically thin disc and the inner hot flow may influence the > precession, and this has not been accounted for in any of the > currently existing models. To address this, we perform GRMHD > simulations of a truncated disc with the inner hot flow misaligned > with the spin axis of the black hole. Our results suggest that the > inner hot flow precesses irrespective of the presence of the outer > thin disc. We also noted that the misalignment excites variability in > the inner hot flow, which is otherwise absent in the aligned discs.


"Searching for low frequency gravitational waves with Pulsar Timing Experiments"

Małgorzata Curyło (Astronomical Observatory, Warsaw University)

While LIGO/Virgo collaboration continues on discovering gravitational waves (GWs) from stellar-mass compact binaries it is worth discussing the current status of projects that probe the lower part of the GW spectrum. In the talk I will present the idea of Pulsar Timing Arrays, which are expected to detect signals from supermassive black hole binaries at nanohertz frequencies. The presentation will focus on the latest major data releases, astrophysical implications and future prospects.


"Long term X-ray time-lags studies"

Angelos Karakonstantakis (CAMK, Warsaw)

The X-ray emission from AGN is highly variable, on short (minutes/hours/day) and long (months/years) time scales. A particular characteristic of the observed variations is that the higher energy band variations are delayed with respect to lower energy photons. I will present the long term, frequency dependent, X-ray time-lags of the Seyfert galaxies NGC 4051, MCG-6-30-15, Ark 564 and Mkn 766 in the 2-4, 4-7, and 7-10 keV bands. I will combine these results with the results from the model fitting of the time lags at higher frequencies to investigate if these delays at low frequencies are consisted with the time-lag estimates at higher frequencies.


"Light particle dark matter in the forward region of the LHC and in astrophysics"

Sebastian Trojanowski (AstroCent, CAMK , Warsaw)

Light and feebly interacting new physics particles with the mass of order the proton mass or lower have become one of the primary targets in both theoretical and experimental studies in (astro)particle physics in recent years with strong connections to dark matter searches. In my talk, I will overview these efforts and the motivations behind them. I will then describe briefly a new physics program dedicated, i.a., to these searches in the far-forward region of the Large Hadron Collider (LHC). Interestingly, such scenarios can also lead to interesting astrophysical bounds that will be presented.


"Metal-poor massive stars: Linking gravitational waves, star-formation and the dawn of the Universe"

Dorottya Szécsi (Uniwersytet Mikołaja Kopernika, Toruń)

What do gravitational waves have in common with ancient globular clusters? What links these to cosmic explosions like gamma-ray bursts, to the energetic radiation in star-forming galaxies and even to the dawn of our Universe? What they have in common, is that all these phenomena — and more — have been theorized to stem from metal-poor massive stars, in one way or another. In my talk, I will explain these theories, and suggest new perspectives on how to combine them.


"Extreme accretion and ejection in ultraluminous X-ray sources"

Ciro Pinto (INAF, Astronomical Observatory of Palermo)

The detection of fully-grown supermassive black holes in active galactic nuclei at high redshifts, when the Universe was young, challenges the theories of black holes growth, requiring long periods of high accretion, most likely above the Eddington limit. These objects will be difficult to probe even with future advanced observatories. Ultraluminous X-ray sources (ULXs) are nearby neutron stars and, perhaps, stellar-mass black holes accreting above their Eddington limit. This was understood after the discovery of coherent pulsations and cyclotron lines in some ULXs, indicating that at least a fraction of them hosts neutron stars as compact objects and, finally, the discovery of powerful winds that were predicted by theoretical models of super-Eddington accreting compact objects. ULX winds carry a huge amount of power owing to their mildly relativistic speeds (~0.1-0.3c) and may be able to significantly affect the surrounding medium, likely producing the observed 100s pc superbubbles, and limit the amount of matter that can reach the central accretor. The study of ULX winds is therefore quintessential to understand 1) how much and how fast can matter be accreted by compact objects and 2) how strong is their feedback onto the surrounding medium in the regime of high accretion rate such as for quasars and supermassive black holes at their peak of growth. I will provide an overview on this phenomenology and highlight exciting results from some recent observational campaigns.


"What was the last Nobel Prize in Physics given for?"

Szymon Malinowski (Department of Physics, Warsaw University)