Wednesday Colloquium


"The Hubble Tension"

Krzysztof Bolejko (University of Tasmania)

One of the most important cosmological discoveries of the last century was the discovery of the expansion of the universe. The expansion rate is measured in terms of the Hubble constant. Throughout the 20th century measurements of the Hubble constant improved. With the improved precision it transpired that high redshift constraints on the Hubble constant are in tension with local measurements. In the recent years this tension has become so prominent that it is now often argued that it will lead to a change of the standard cosmological model (just like in 1990s when supernovae date initiated a shift from the Einstein-de Sitter model to the Lambda-CDM model). In my talk I will discuss the tension in measurements of the Hubble constant. I will also talk about possible directions and avenues of solving this tension.


"Heritage in troubling times"

Monika Stobiecka (Artes Liberales, Warsaw University)

Contemporary age poses serious threats to various material heritage objects and monuments. The climate change, growing nationalism, military conflicts, as well as quick technological progress, redefine our realities and affect the ways in which we perceive heritage. No longer can we think about traditional forms of protected monuments, when those are exposed to instrumentalization, abrupt changes and/or destruction. In my presentation, I would like to discuss three important factors shaping today’s heritage: politics, technologies and climate change. Those problems will be illustrated with my previous researches on art and archaeology, namely the Zakopane style (politics), the copy of the Syrian Arch (technologies), and the ruins of Petra (climate change).


"Wind fed accretion onto Cygnus X-1"

Ishika Palit (Center for Theoretical Physics, PAN, Warsaw)

Cygnus X-1 is a black hole X-ray binary system with a companion, supergiant star, HDE-226868. It is one of the brightest X-ray sources observed and shows the X-ray intensity variations in both the soft and hard X-rays. The focused stellar wind from the supergiant provides the source of the matter accreting into the black hole and thus also affects the observed spectral states. I will present my recent work on 2D numerical modeling replicating such focused, clumpy wind from the binary companion fed for accretion onto the black hole. Further, I will discuss the role of shock oscillation in the aspect of the observed variability in Hard X-rays and will present our results from Power Density Spectral (PDS) analysis


"Towards Understanding Black Hole Accretion and Jet Launching"

Monika Mościbrodzka (Radboud University, Nijmegen)

The Event Horizon Telescope (EHT) is a global effort to construct an Earth-sized virtual radio telescope array, with the ultimate goal to actually make pictures and movies of some nearby supermassive black holes. The initial results of the first full EHT observing run in 2017 were presented on 10 April 2019. A detailed theoretical understanding of black hole astrophysics is now very crucial to interpret these observations. The focus of the talk is on modeling intensity and polarimetric properties of light produced in synchrotron processes in plasma falling towards the event horizon. In particular the polarized component of light gives us detail constraints on the magnetic field geometry and dynamics at the event horizon, which are keys to understand the accretion and jet launching process.