Wednesday Colloquium



Paweł Nurowski (Center for Theoretical Physics, Warsaw)


"The structure of Andromeda II dwarf spheroidal galaxy"

Andrés del Pino (NCAC, Warsaw)

The Andromeda II dwarf spheroidal galaxy (dSph) is one of the most conspicuous systems in the Local Group. It is known to host at least two stellar populations, different in age and metallicity. Furthermore, Andromeda II shows a strong rotation signal, comparable to its central velocity dispersion. This feature, not common in dSph galaxies, is even more surprising since the rotation direction is around the optical major axis of the galaxy. In this talk we present the results of the most comprehensive analysis of Andromeda II up to date. We analyze in detail the spatial distribution and kinematic properties of the two stellar populations. We demonstrate for the first time that both populations are also separated in their kinematics and that might not be in equilibrium. Finally, we will discuss possible scenarios for the origin and evolution of the galaxy.


"Asteroseismology in Close Binaries: Delta Scuti Stars and Tidally Induced Pulsations in Heartbeat Stars"

Zhao Guo (NCAC, Warsaw)

Great advancements have been made in understanding solar-like oscillators. However, this is not the case for variable stars of intermediate masses, such as Delta Scuti variables. By studying these stars in eclipsing binaries (EBs), model independent fundamental parameters such as mass and radius can be inferred. On one hand, this synergy constrains the parameter space and facilitates the asteroseismic modeling, and this is shown for the Delta Scuti type pulsating EB KIC 3858884 and KIC 9851944. On the other hand, studies of binary stars must address the complexities such as mass transfer. KIC 8262223 is such an example, which consists of a mass-gaining Delta Scuti primary and a pre-He white dwarf secondary. Some of the eccentric binary systems, the heartbeat stars, show tidally excited oscillations. After briefly reviewing the linear theory of tidally forced stellar oscillations, we study the tidal pulsating binary KIC 3230227 and demonstrate that both amplitude and phase can be used to identify the tidally excited pulsation modes.


"New forms of pulsation in classical pulsators"

Radosław Smolec (NCAC, Warsaw)


"MOCCA-SURVEY Database I Projects: Binary Black Holes and IMBHs in Globular Clusters"

Abbas Askar (NCAC, Warsaw)

Modeling the evolution of extremely dense stellar systems like globular clusters remains a challenging astrophysical problem. In this talk, I will briefly introduce the basic ideas behind the Monte Carlo method for simulating the long term evolution of star clusters and will describe the MOCCA (MOnte Carlo Cluster simulAtor) code and its features. My talk will focus on the results from two projects that utilized the results of the MOCCA-SURVEY Database I project in which about 2000 star cluster models were simulated using the MOCCA code. In the first project, we used the results from this database of star cluster models to determine the astrophysical properties and local merger rate densities for coalescing binary black holes. In the second project, we describe the dynamical evolution of a unique type of dark star cluster model in which the majority of the cluster mass at Hubble time is dominated by an intermediate mass black hole (IMBH). Taking one of these models, we apply the method of simulating realistic mock observations to obtain the photometric and kinematic observational properties of the dark star cluster model at 12 Gyr. We find that the perplexing Galactic globular cluster NGC 6535 closely matches the observational photometric and kinematic properties of the dark star cluster model and could potentially be harbouring an IMBH. I will also briefly mention other ongoing projects that are using results from the MOCCA-SURVEY Database I project and future plans to further improve and carry out more simulations.


"On Cataclysmic Variables in Globular Clusters"

Diogo Belloni (NCAC, Warsaw)

Cataclysmic variables are interacting binaries composed of a white dwarf undergoing stable mass transfer from (usually) a low-mass main sequence star and they are expected to exist in non-negligible numbers in globular clusters that are natural laboratories for testing theories of stellar dynamics and evolution. I will present the main aspects related to our understanding regarding the population of cataclysmic variables in globular clusters from two points of view: numerical simulation and observations. I will conclude by summarizing some key procedures associated with the fate of the research in such a field, including the role of our group in the process.


"New Scenario for IMBH Formation in Star Clusters - Tidal Disruption Events"

Mirosław Giersz (NCAC, Warsaw)

I will discuss recent developments in the new scenario for intermediate mass black hole (IMBH) formation in dense star clusters. In this scenario, an IMBH is formed as a result of a dynamical interactions of a hard binary, containing a stellar mass black hole (BH), with other stars and binaries. The mass of the BH constantly increases due to mergers with incoming stars and mass transfer from companions. The recent developments are connected with the relation of the new scenario to the well known runaway scenario and to the tidal capture scenario, just recently described in an excellent paper by Stone, Kupper & Ostrilker (2016). I will also discuss, with relation to the new scenario, observational imprints of the presence of IMBH in star clusters. These imprints are connected with particular features of electromagnetic and gravitational wave radiations and properties of binaries containing IMBH.


"The jet propagation in the external environment of the Long GRB Collapsar – The Rarefaction Process"

Konstantinos Sapountzis (Center for Theoretical Physics, Polish Academy of Sciences, Warsaw)

The widely accepted model for the Long Gamma Ray Burst progenitor is based on the core collapse of a Wolf-Rayet star (Collapsar) and the consequent launching of jets that penetrate the stellar envelope and continue their propagation in the interstellar medium. The transition from a high pressure environment that supports the jet (star interior) to an environment of reduced external pressure (interstellar medium) results in the formation of shock and weak discontinuities in the outflow body. These formations correspond to areas where significant energy conversions take place and they can give answers to the open questions of the prompt emission origin. The Rarefaction phenomenon is well studied for the newtonian and unmagnetized flows, but for the hyper-relativistic and magnetic dominated limit, as expected in the Collapsar model, the issue is open and only recently studies were performed mostly by means of numerical simulations. In order to clarify the physical interpretation of the magnetized phenomenon, we constructed a semi-analytical model consisting of the self similar solutions of the planar equations. This model provides valuable insight for the energetic conversions and the spatial scales they take place, while the scaling laws and estimations extend their validity also to the Collapsar outflow. At the second part, we present an algorithm we built based on the system characteristics that integrates the axisymmetric system and we study the implication that the axisymmetry induces. Finally, we conclude with the verification of our results by the use of other familiar numerical algorithms (PLUTO).


"Close binary central stars of planetary nebulae"

Brent Miszalski (SAAO, SA)

Planetary Nebulae (PNe) are a brief phase in the lives of low to intermediate mass stars where the atmosphere of an asymptotic giant branch star is ejected and ionised by the hot leftover core that eventually becomes a white dwarf. They appear in an extremely wide variety of shapes, but exactly how they are shaped into such a diverse range of morphologies is still highly uncertain despite over thirty years of vigorous debate. Binaries have long been thought to offer a solution to this vexing problem, but only now we are beginning to understand the important role that a binary channel, in particular common-envelope (CE) evolution, plays in the formation of a large fraction of PNe. I'll give an overview of results in this area and show how binary central stars are connected to many other aspects of stellar astrophysics. An important corollary of this work has been the much improved understanding of jets in PNe. I'll conclude the talk with highlights of results from observations with the Southern African Large Telescope (SALT) aimed at discovering more unusual binary central stars.


"Pulsar glitches, a tool to study the neutron star interior"

Danai Antonopoulou (NCAC, Warsaw)

Sudden spin-ups of a neutron star, called glitches, were first detected shortly after the discovery of the first pulsars. To date, about 500 glitches have been observed in over 100 sources. Glitches seem to be common across different types of neutron stars, like young, rotationally-powered radio and/or high-energy pulsars, magnetically-powered anomalous X-ray pulsars and RRATs - which are objects with intermittently pulsed radio emission. Because the spin-up and its subsequent relaxation are thought to be driven by an internal neutron superfluid component, their study provides one of the few direct probes into the dynamics and physics of the neutron star interior. I will present the process of detecting and measuring glitches, their characteristics, and some of the physical information we can extract from such observations.


"Cosmic butterflies: the product of tempestuous stellar marriages"

David Jones (Instituto de Astrofísica de Canarias)

Planetary nebulae are some of the most strikingly beautiful astrophysical phenomena known, gracing many a glossy-paged, coffee-table book and earning them the nickname "cosmic butterflies". It is now clear that a significant fraction of these objects originate from a binary evolutionary pathway, with some theories even going as far as to say that binarity may be a prerequisite for all but the most massive stars to form a planetary nebula. In this seminar, I will begin by outlining some fundamentals of close binary evolution and how they relate to the formation of planetary nebulae. I will then go on to discuss some of our most interesting results, what they can tell us about the common envelope phase of close binary evolution, and the growing connections between these systems and other binary phenomena including novae and supernovae type Ia.


"Discovery of a new class of pulsating stars"

Paweł Pietrukowicz (Astronomical Observatory, Warsaw University)

Thousands of pulsating stars have been detected in the Milky Way and other galaxies of the Local Group over the last decades mainly thanks to large-scale variability surveys. It seemed that all types of pulsating stars had been recognized. By monitoring about one billion stars in the sky, the OGLE survey has discovered extremely rare, short-period objects whose properties do not fit to any class of known pulsators. Theory shows that the newly discovered objects are evolved low-mass stars with a giant-like structure, but their origin remains a mystery.


"A simple approach to gravitational wave data analysis"

Tomasz Bulik (Astronomical Observatory, Warsaw University)

The recent discovery of binary black hole coalescence by LIGO is based on a few cycles seen in a fraction of a second. I will show how the information about the binary can be inferred from the observed variation of the signal in time using only basic physical arguments.


"Tight galaxy scaling relations: a challenge to galaxy formation models "

Benoit Famaey (Observatoire Astronomique de Strasbourg)

In this talk, we review the observational evidence for an intimate connection between the baryonic surface density and the total gravitational field in galaxies. This observational fact presents a fine-tuning problem for the particle dark matter interpretation of mass discrepancies in galaxies. We show that this is the case even when taking baryonic feedback into account. On the other hand, this is naturally explained within the MOND paradigm, hypothesizing an effective breakdown of Newtonian dynamics in the extremely low acceleration regime. However, MOND clearly breaks down on scales larger than galaxies, where there is ample evidence for a new degree of freedom behaving as a collisionless fluid of particles, i.e. dark matter. Theories modifying the lagrangian of the dark matter sector to account for the baryon-dark matter connection in galaxies while preserving the predictions of LambdaCDM on the largest scales might perhaps be a promising way to reconcile these conflicting observational facts.


"Magnetic relaxation and turbulence in pulsar wind nebulae"

Jonathan Zrake (Columbia University)

Pulsar wind nebulae (PWNe) are energized by the electromagnetic spin-down power of a rapidly rotating neutron star. Their emission is primarily synchrotron, produced by relativistic electrons radiating in a sub-equipartition magnetic field. The processes by which a pulsar wind, which is born in a strongly magnetized state, eventually shares its energy with electrons, has been a long-standing question in the theory of pulsars and their nebulae (sometimes referred to as the sigma-problem). I will discuss how dissipation in PWNe may be understood in terms of a process known as magnetic relaxation, and give an overview in general physics terms of recent advances in this topic. MHD simulations reveal the process is generally turbulent, and that magnetic field structures tend to organize themselves spatially, even when the field lacks net magnetic helicity. I will discuss how this process helps to explain the magnetization level of the Crab's synchrotron nebula.


"Evolution and pulsations of massive stars with the effects of rotation and mixing processes"

Jakub Ostrowski (Uniwersytet Wrocławski)

Massive stars are often fast rotators and they are subject to various mixing processes. Both stellar rotation and mixing are not perfectly understood and their proper implementation into stellar evolution codes is complex. However, they play a central role in modern stellar modelling due to their overwhelming influence on stellar structure and theoretical oscillation spectra. Moreover, rotation and mixing are two closely related subjects. Presence of differential rotation leads to emergence of many instabilities. They contribute to transport of chemical elements and angular momentum in the stellar interiors. During my lecture I plan to assess how rotation and mixing processes are implemented in a modern evolution code - MESA and discuss their influence on massive stellar models, which I have calculated. My aim is to demonstrate how sophisticated rotating models have provided us with a way to constrain various stellar parameters of HD 163899 - the prototype of Slowly Pulsating B-type supergiants.


"Nova Scorpii 1437 A.D. - now a cataclysmic variable"

Joanna Mikołajewska (NCAC, Warsaw)

I will present and discuss a recovery of the binary underlying the classical nova of 11 March 1437 recorded by Korean royal astronomers whose age is independently confirmed by proper motion-dating.


"Back to the future: highlights of the observing campaign of the large scale jets of XTE J1550-564"

Giulia Migliori (Université Paris Diderot)

The large-scale decelerating jets of the XTE J1550-564 represent an unique laboratory to investigate the physics of microquasars’ jets and their interaction with the interstellar medium In this talk, I will present the results of the multi-frequency campaign of observations which probed the inner structure of the western jet in 2001-2003. The complex, evolving morphology of the jet in X-rays, the detection of polarized radio emission and the chromatic decay of the broad-band emission give indications on how the particles are accelerated and energy is dissipated at large distances from the black hole. I will discuss our findings in relation to the radiative and dynamical models proposed for this system, and examine the similarities with other microquasars’ jets, such as H 1743-322. Finally, I will briefly illustrate how the incoming facilities will significantly improve our powers of observations of this class of transient objects.


"The Greatest Myth in the History of Astronomy"

Owen Gingerich (Harvard University)


"Wildly oscillating stars - a new physical phenomenon? Eliminating the impossible to find the improbable"

Victoria Antoci (University of Aarhus)

Here I present our photometric and spectroscopic analyses of a sample of gamma Dor and hybrid pulsators that exhibit (additional) frequency patterns inconsistent with anything we know about these type of stars. More precisely we find peaks, that show nice long ridges reminiscent of consecutive high radial order g-modes, however, their period spacings do not match the expected values for main sequence stars but rather those of compact objects. On the other hand, if we assume that the peaks are split in frequency instead of periods we find repeating patterns of multiplets reoccurring in a very narrow frequency range. This phenomenon occurs in a significant number of stars, not always at the same frequency and with the same separation, which leads us to conclude that these signals are intrinsic to the stars and may describe a new phenomenon in A and F stars on and near the main sequence.


"GRB light curve decay indices in the afterglow phase"

Roberta Del Vecchio (Astronomical Observatory, Jagiellonian University)

I will start with presentation of basic information about cosmic Gamma-ray Burst (GRB) phenomenon. Then our study of the distribution of temporal power-law decay indices, α, in the GRB afterglow phase will be described, based on a sample of 176 GRBs with known redshifts. In this analysis we discovered a convincing regular trend between α and the afterglow luminosity at the end time of the plateau phase, La. Even stronger systematic trend is visible between and the luminosity ratio computed by dividing La by the respective luminosity at the fitted Luminosity-Time correlation line (Dainotti et al. 2008). This systematic effect provides a new constraint on the GRB physical models. Finally, a proposed toy model accounting for this systematics applied to the luminosity of the analyzed GRB distribution results in a slight decrease of the scatter within the LT correlation, possibly a small step towards turning GRBs into cosmological standard candles.


"Dark energy as silent virialisation"

Boud Roukema (Astronomical Observatory, Toruń)

The Friedmann-Lemaitre-Robertson-Walker cosmological solutions of the Einstein equation assume a stress-energy tensor with positive density and zero pressure. These solutions do not allow for gravitational collapse on galaxy and galaxy cluster scales. Gravitational collapse and virialisation, together with general spatial expansion, can be modelled by either (i) assuming stable clustering in virialised domains (D) and the kinematical backreaction (Q_D) Zel'dovich approximation (ZA) for normal volume evolution (VQZA); or, equivalently, (ii) defining a negative effective gravitational pressure that locally opposes gravitational attraction, thus enabling virialisation to be represented, with a stable end state p_D = -_D/3. The silent universe hypothesis is assumed in both cases. An implementation of (i) VQZA will be presented. This shows that scalar averaging with a domain size of a typical non-linear structure scale, about 2.5 Mpc/h, yields "dark energy" as an artefact of ignoring virialisation in the stress-energy tensor.


"X-ray emission from the hot halo gas and its AGN link"

Priyanka Singh (Raman Research Institute)


"Records of Primordial Gravitational Waves in the Cosmic Microwave Background: Status, Challenges and Prospects for present and future B-mode CMB experiments"

Carlo Baccigalupi (SISSA, Triesste)

We review the mechanisms leading to Gravitational Waves imprint in the B-modes of Cosmic Microwave Background Polarization Anisotropy. We discuss the current status of measurements, and the main challenges towards future precision measurements, focusing on the diffuse polarization emission from our own Galaxy. Finally, we outline the path ahead in terms of operating and planned CMB B-mode experiments.


"Gravitational Wave Detection and Parameter Estimation"

Matthew Benacquista (University of Texas)

In light of the recent detections of gravitational waves from binary black holes with LIGO/Virgo, I will discuss the physics of the generation, propagation, and detection of gravitational waves with an emphasis on parameter estimation. In particular, I will highlight the uncertainties and selection effects in the observations and the limitations in determining the origin of these sources.


"Testing General Relativity with gravitational waves"

Michał Bejger (NCAC, Warsaw)


"Hierarchical formed young star clusters: Is resistance to gas-expulsion really futile?"

Michael Fellhauer (Departamento de Astronomia Universidad de Concepcion)

In this talk I will review the work of our group on the dynamics of young embedded star clusters and their survival to gas-expulsion. With our simplified N-body models we have established a new theory to predict the survivability of young star forming regions to gas-expulsion. Using more advanced models we then have shown that those clusters should rather populate the region in parameter space which allows them to survive very well. I will also show what we think are the new gang of culprits for the destruction of young small star clusters, a process dubbed infant mortality.


"The Astrophysics of BH-BH/NS-NS Mergers with LIGO/Virgo"

Krzysztof Belczyński (Copernicus Astronomical Center, Warsaw)

I will discuss the astrophysical importance of the recent LIGO direct detections of gravitational-waves. Despite majority of the expectations, it was not neutron star mergers being detected, but the series of exotic massive black hole mergers. I will discuss the leading theories of the formation of such black hole systems. I will also comment on a potential (rumored) detection of NS-NS merger in the current LIGO/Virgo data. If true it may provide striking constraints on binary evolution predictions. Several astrophysical implications are beginning to emerge despite the fact that the exact origin of LIGO/Virgo sources is not yet known.


"Chemical Evolution of Galaxies from Nuclear Astrophysics to Cosmological Structure Formation"

Benoit Côté ( Konkoly Observatory of the Hungarian Academy of Sciences)

Galactic chemical evolution (GCE) is a multidisciplinary topic that involves nuclear physics, stellar evolution, galaxy evolution, observation, and cosmology. Observations, experiments, and theories need to work together in order to build a comprehensive understanding of how the chemical elements synthesized in astronomical events are spread inside and around galaxies and recycled into new generations of stars. The purpose of GCE is to better understand the origin of the elements in the universe and to use chemical abundances to investigate how galaxies form and evolve in a cosmological context. During this talk, I will introduce the basics of GCE and present our efforts to create permanent connections between different fields of research (including nucleosynthesis and gravitational wave physics). In particular, I will present how we used our tools to investigate the possible production sites of light and heavy elements, to quantify output uncertainties and the impact of different modeling assumptions in galaxy models, and to study how structure formation (galaxy mergers) affects the chemical evolution of galaxies in the early universe.


"Non-standard cosmological tests of gravity"

Wojciech Hellwing (Center for Theoretical Physics, Polish Academy of Sciences, Warsaw)

GR is a "perfect" theory that in the last century successfully undergo many stringent observational tests. Its unchallenged position in both small (Solar System) scales and strong field limits (i.e. BH and NS) made it a natural candidate for the fundamental building block for standard cosmological model (LCDM). However, GR has not been so far rigorously tested in the very low-densities and at intergalactic scales. Thus the reality doors are still quite open for many prospective alternative theories commonly dubbed Modified Gravity. I shall recapture the general landscape of the currently very vibrant field of modified gravity theories. I will also discuss why is it absolutely crucial to find and provide as many as possible independent cosmological tests of GR and its competitors. Finally, I will present some of quite non-standard cosmological tests of gravity that me and my collaborators have put forward recently. These include hierarchical amplitudes (scaled higher-order central moments of the density field) and halo/galaxy clustering ratios.


"Adventures with blazar 3C 279"

Krzysztof Nalewajko (CAMK, Warsaw)

I will present a story of 3C 279, one of the most thoroughly investigated blazars. This will include my own efforts, starting in 2009, in close collaboration with Grzegorz Madejski, Masaaki Hayashida and Marek Sikora.


"Infrared features in the ISM and host galaxies of Young Radio Sources"

Emily Kosmaczewski (Rensselaer Polytechnic Institute (Troy, NY))

I will present on the importance of tracing infrared features in interstellar medium and in the host galaxies of young radio sources. Specifically, I will show the breakdown of polycyclic aromatic hydrocarbon (PAH) infrared emission features, the analysis and fitting of such features, the importance of certain features as tracers for star activity, as well as key correlations in the analysis of ISM.


"50 Years of Pulsars"

Bryn Haskell (NCAC, Warsaw)

Neutron stars are the most exotic nuclear physics laboratories in the universe. With a mass similar to that of the sun, packed in a 10 km radius, their interior densities can exceed nuclear density, and constituents are expected to be superfluid and superconducting. These stars also carry some of the strongest magnetic fields in nature (more than a million times that of the Earth, even for the most weakly magnetised stars), and thus allow us to probe the fundamental forces of nature in extreme conditions. Neutron stars were first observed 50 years ago as pulsating radio sources, or 'pulsars'. In this talk I will review this discovery and what we have learned in these 50 years, including how neutron stars can be used to test general relativity, explore high density physics and even detect gravitational waves.


"Galaxies with prolate rotation in the Illustris simulation"

Ivana Ebrova (NCAC, Warsaw)

Tens of early type galaxies have been recently reported to possess prolate rotation, i.e. significant amount of rotation around the major axis, including two cases in the Local Group. Although expected theoretically, this phenomenon is rarely observed and remains elusive. In order to explore its origin we study the population of well-resolved galaxies in the Illustris cosmological simulation. We follow their evolution back in time and find that the emergence of prolate rotation is strongly correlated with the time of the last significant merger the galaxy experienced. We examine properties of these mergers and compare them with mergers in the reference sample of galaxies drawn from Illustris.


"Superfluid neutron stars: from pinning forces to pulsar glitch amplitudes"

Marco Antonelli (Milano)

Neutron stars are extreme physics laboratories, allowing us to probe aspects of dense matter that cannot be tested on Earth. Issues involving nuclear superfluidity are though to play key roles for neutron star phenomenology. In particular pulsar glitches (sudden jumps in the period of otherwise steadily spinning down pulsars) offer a glimpse into the superfluid interior of a neutron star: within the currently accepted scenario these timing irregularities are explained in terms of an expulsion of the quantized vortex lines that permeate the superfluid in the crustal region of the star. Vortices can pin to the ions in the crust, providing the mechanism for storing the angular momentum that can be eventually released during a glitch. A simplified model for the angular momentum reservoir of pinned vorticity gives a general and quantitative inverse relation between size of the maximum glitch and the pulsar mass: I'll present a method to put some limits on the mass of a pulsar, using observations of the maximum glitch observed, together with models of the pinning interaction between superfluid vortices and ions in the crust. This procedure procedure will hopefully allow current and future pulsar timing observations to constrain the physics of glitch models and pinning forces.


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

Tomasz Bulik (Astronomical Observatory, Warsaw University)

This year Nobel Prize in Physics was awarded for „decisive contributions to the LIGO detector and the observation of gravitational waves”. I will summarize the path that lead to construction of LIGO and to the direct detection of gravitational waves. I will outline the current state and the future for gravitational wave astronomy.