Institute of Astronomy

ContactPiwnice k. Torunia, 87-148 Łysomice
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General Seminar (2024)

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General Seminar takes place every Monday at 11.15 in Piwnice, radioastronomy seminar room.
Remote participation via the BigBlueButton (BBB).

8 January 2024


15 January 2024

“Interstellar medium of spiral galaxies heated by magnetic reconnection?”

dr Marek Weżgowiec (Astronomical Observatory, Jagiellonian University)

In several face-on spiral galaxies a similar spiral structure of the ordered magnetic fields have been observed using sensitive radio polarimetry. These so-called magnetic arms are ‘phase-shifted’ with the spiral arms and their nature is not fully understood. This behaviour of the magnetic fields might be explained by magnetic reconnection that would increase their ordering. Theoretical studies show that magnetic reconnection at the same time can efficiently heat the low-density interstellar medium. To study both effects in more detail we used the XMM-Newton X-ray data and the VLA/Effelsberg radio polarimetric data for several galaxies in which the magnetic arms were found. We compared the properties of the magnetic fields (strengths and energy densities) and of the hot gas (temperatures and energy densities) in selected areas of galactic disks. The analysis revealed signatures of possible increase in thermal energy of the hot gas that can be attributed to the action of magnetic reconnection effects. This seems to be more easily detected in the inter-arm regions than in the spiral arms of galaxies. Our studies also suggest that such ‘reconnection heating’ may be also efficient in galactic halos, where the density of the ISM is lowest.

22 January 2024

“Chemically-homogeneously evolving stars in the dwarf galaxy IZw18?”

dr Dorottya Szécsi (Institute of Astronomy, Nicolaus Copernicus University)

Chemically-homogeneously evolving stars have been proposed to account for several exotic phenomena, including gamma-ray bursts, gravitational-wave emissions and certain types of supernovae. Here I show how these stars can account for observations of the metal-poor dwarf galaxy, I Zwicky 18. Applying new PoWR synthetic spectral models to predict the photonionizing flux and the strength of observable stellar lines from a I Zw 18-like population, we compare the results to all available optical and UV data from the literature. We show that the measurements are consistently explained by our models. The source of the stellar emission, such as the UV C-IV (λ1550 Å) line, is a handful of WN and/or WO-type Wolf–Rayet stars (skipping the WC phase completely, which contradicts what was previously assumed), while the high He-II ionizing flux is accounted for by the chemically-homogeneously evolving stars which happen to be extremely hot.

29 January 2024

“Towards a holistic understanding of sub-Neptunes.”

dr Rafael Luque (Department of Astronomy and Astrophysics, University of Chicago)

The nature and origin of sub-Neptune-sized planets is arguably the hottest debate in the field of exoplanets nowadays. While absent in the Solar System, they are the most common planet type in the Galaxy. Multiple models (gas dwarfs, water worlds, Hycean planets) appear to explain current observational evidence from mass-radius measurements and demographic analyses. JWST promises to break those degeneracies, but the first robust results are yet to be published. In the meantime, the discovery and characterization of benchmark targets amenable for these studies is the top priority. In this talk, I will give an overview of the questions surrounding the origin of the “Radius gap”, recent sub-Neptune discoveries such as the 6-planet resonant chain orbiting HD 110067, and the latest efforts in the community to detect molecular species in their atmospheres.

5 February 2024

“Populations of short-period super-Earths, sub-Neptunes, and Neptune-sized planets and prospects for their atmospheric characterisation”

dr Grzegorz Nowak (Institute of Astronomy, Nicolaus Copernicus University)

Space-based, high-precision photometric missions to detect transiting planets, such as CoRoT, Kepler, Kepler-K2 and TESS, have revolutionised our understanding of extrasolar planets, particularly for the smallest planets of 1-4 Earth radii. Probably the most important result we owe to the original Kepler mission is a bimodal structure in the radius distribution of the close-in (Pp < 100 d) small planets, with a gap around 1.7 R_Earth that separates the two main classes of small planets: presumably rocky super-Earths with radii around 1.2 R_Earth, and sub-Neptunes with radii around 2.4 R_Earth. Detailed studies of the population of small planets with short periods require precise dynamical mass measurements via radial velocities. These measurements, together with radius, provide information about the bulk densities of the planets. However, measurements of mass, radius, and mean density alone are insufficient to answer all questions about their origin, initial formation location, and internal composition. But since different classes of small planets should have different atmospheres with different observable signatures, their atmospheric studies should help us a lot to answer the above questions. In this talk, I am going to present recent radial velocity follow-up results from TESS planetary systems with small planets and prospects for their atmospheric characterisation. These results include two warm Neptunes transiting HIP 9618, four sub-Neptunes orbiting the K dwarf TOI-1246, TOI-1416 - a system with a super-Earth planet with a period of 1.07 days, and TOI-1136 - a new TESS system with six confirmed transiting sub-Neptunes and Neptunes in resonance, and a seventh single-transiting planet candidate around a young (~700 Myr), active G5 dwarf.

26 February 2024

“Tangle of Chaos in Standing Gravitational Waves”

MSc Syed Naqvi (Astronomical Observatory, Jagiellonian University)

Standing waves, well-studied in mechanical and electromagnetic domains, have been studied within the Einstein-Rosen spacetime, representing cylindrical standing gravitational waves. Our study aimed to analyze the behavior of test particles’ orbits within this spacetime. We observed a sensitivity to initial conditions in the trajectories of these particles. Additionally, we discover the fractal associated with this system. Examining the Poincare map, we identified intricate crossings of stable and unstable manifolds at hyperbolic fixed points. A chaotic heteroclinic network further characterized the complex dynamics of massive test particles. Analogous to phenomena such as mechanical vibrations generating Chladni figures and the intricate shapes of Faraday waves, gravitational standing waves produce complex patterns through the interactions of test particles.

4 March 2024

“Clouds vs Cherenkov telescopes: problems and solutions”

prof. dr hab. Julian Sitarek (Computer Simulations Laboratory, University of Łódź)

Very-high-energy (VHE >~100 GeV) gamma rays are absorbed in Earth’s atmosphere and thus cannot be detected directly on Earth. Their fluxes are also typically too low to efficiently study them with satellite instruments. A VHE gamma ray entering the atmosphere initiates an electromagnetic cascade that induces faint flashes of blueish Cherenkov light. Such flashes can be then detected by Imaging Atmospheric Cherenkov Telescopes registering images of passage of individual gamma rays through the atmosphere. The usage of atmosphere as a part of the detector allows us to achieve a collection area of gamma rays over two orders of magnitude higher than the physical size of the detector. But it also introduces systematic errors connected with the atmosphere’s transparency. In particular, cloud presence during the observations can significantly affect the data. In this seminar I will cover different methods used to correct the influence of the clouds. I will show how lack of such a correction introduces bias in the energy estimation of gamma rays. I will present how the affected images of showers are degraded and thus can be confused with background events, lowering the collection area of the telescope. Finally, I will show a novel method of correcting the influence of the clouds already at the image level, and discuss the possibility of measuring the parameters of a cloud directly with the observations by the Cherenkov telescopes.

11 March 2024

“4MOST: the 4-metre Multi-Object Spectroscopic Telescope”

prof. dr hab. Boudewijn Roukema (Institute of Astronomy, Nicolaus Copernicus University)


18 March 2024

“Magnetic flux saturation mechanism at accreting black holes”

dr hab. Krzysztof Nalewajko, prof. CAMK PAN (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences)

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.