Wednesday Colloquium

 future talks and archive

The Colloquium takes place every Wednesday at 11:15 AM - Warsaw Copernicus Astronomical Centre online by means of Zoom platform. The Colloquium is given in English and chaired by dr Stanisław Bajtlik ( from outside of the Copernicus Center are very welcome to participate. For technical detailes please contact Dr. Stanislaw Bajtlik.


"Physical units and the new SI"

Grzegorz Łach (Department of Physics, Warsaw University)

In 2019 the SI system of units underwent a major redefinition — removing any use of physical artifacts as unit standards. Since then all the units are defined based on fundamental physical phenomena. As a consequence several fundamental constants such as the Planck's and the Boltzmann constants have been permanently fixed. I will describe some of the motivations behind this reform, the choices which had to me made, and the use of current definitions in practice.


Special seminars


Journal Club

 future talks and archive

Journal Club takes place on Mondays at 11:00 AM in the room 18/19. The seminar is given in English and is chaired by Angelos  Karakonstantakis, Gergely Hajdu, and Fatemeh Kayanikhoo.


"The Accretion Flow in M87 is Really MAD"

Angelos Karakonstantakis (NCAC, Warsaw)

The supermassive black holes in most galaxies in the universe are powered by hot accretion flows. Both theoretical analysis and numerical simulations have indicated that, depending on the degree of magnetization, black hole hot accretion flow is divided into two modes, namely SANE (standard and normal evolution) and MAD (magnetically arrested disk). It has been an important question which mode the hot accretion flows in individual sources should belong to in reality, SANE or MAD. This issue has been investigated in some previous works but they all suffer from various uncertainties. By using the measured rotation measure (RM) values in the prototype low-luminosity active galactic nuclei in M87 at 2, 5, and 8 GHz along the jet at various distances from the black hole, combined with three-dimensional general relativity magnetohydrodynamical numerical simulations of SANE and MAD, we show in this paper that the RM values predicted by MAD are well consistent with observations, while the SANE model overestimates the RM by over two orders of magnitude and thus is ruled out.

Yuan, Feng et al., The Astrophysical Journal (2022)

Yuan, FengYuan, Feng


The Bohdan Paczyński Memorial Colloquium



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