Tomasz Miller (Copernicus Center, Jagiellonian University, Cracow)
In the late 19th century, Georg Cantor made a stunning discovery: in mathematics there is not just a single infinity, but an infinite hierarchy of "transfinite numbers." In my talk, I will briefly recall how this "Cantor’s paradise" (as Hilbert called it) is constructed. I will then turn to a more recent attempt to tame infinity, initiated by John H. Conway, who went on to discover an even richer - in a sense "ultimate" - number system: the surreal numbers. This system contains not only Cantor’s transfinites but also their reciprocals, the infinitesimals. I will close by reflecting on a natural question: why study such abstract objects at all?
Andrzej Zdziarski (CAMK, PAN, Warsaw)
In recent years, spins of merging black holes have been measured with relatively high accuracy from their gravitational-wave signals. They are generally low, with the estimated average effective spin parameter close to null. On the other hand, spins of many accreting black-hole binaries have been measured to be high, some close to the maximum spin parameter of 1, e.g., greater than 0.9985 at 3 sigma in Cygnus X-1. I will present our recent results regarding this discrepancy. In particular, I will discuss possible systematic effects affecting spin measurements in accreting systems and whether they can be reconciled with those from gravitational-wave observations. See New Astronomy Reviews (2026), 102, 101746 (arXiv:2506.00623).
Arpita Misra (Jagiellonian University, Cracow)
Supermassive black hole (SMBH) spin plays a central role in shaping relativistic jets, yet direct measurements of spin and its evolution remain challenging. Radio jets provide an indirect yet powerful probe of SMBH spin dynamics through their morphology, orientation, and temporal behavior. The radio galaxies exhibiting X-shaped or S-shaped jets are key candidates to study the spin evolution as they highlight a dynamic interplay between the jets, the central active region, and the intergalactic medium. In this talk, I will present observational evidence linking the jet properties of winged radio galaxies to the evolving spin of SMBHs, primarily focusing on S-shaped radio galaxies. Using multiwavelength and multi-frequency radio data, I will discuss how features such as jet reorientation, spectral aging, and large-scale morphology in post-merger and merging systems offer insights into changes in the spin axis. These results highlight the role of radio jets as tracers of SMBH spin evolution and demonstrate how detailed radio studies can constrain the physical processes governing black hole growth and feedback across cosmic time.
Daniela Turis-Gallo (Universidad de Valparaiso, Chile)
Juan Pablo Hidalgo (University of Rome)
Large-scale magnetic fields have been observed in about 10% of main-sequence early-type stars. Notably, chemically peculiar Ap/Bp stars can host surface magnetic fields with mean strengths between 200 G and 30 kG. Unlike late-type stars, whose magnetic fields have complex geometries and are likely generated by convective dynamos, the observed magnetic fields of early-type stars have simpler geometries, and are stable over long timescales, with virtually no variability over several decades. Because these stars have thick radiative envelopes and convective cores, surface dynamos are unlikely to account for the observed magnetism. Consequently, the origin of these magnetic fields remains uncertain. In this talk, I will review recent progress in some of the main theories proposed to explain the magnetism in early-type stars, exploring dynamos hosted by their convective cores, and their interaction with fossil fields inherited from earlier evolutionary stages. Furthermore, I will discuss ongoing simulations of pre-main-sequence stellar evolution aimed at constraining the structure and properties of these primordial fields.
Dominika Król (Harvard Smithonian CfA)
Maciek Wielgus (Instituto de Astrofísica de Andalucía, IAA-CSIC, Granada, Hiszpania)
Laetitia Gibaud (Department of Physics, University of Białystok)
