Wednesday Colloquium


"Simulating globular cluster populations around Milky Way and Andromeda-like galaxies with MOCCA models"

Agostino Leveque (CAMK, PAN)

The ability to model both the large-scale dynamics (0.01-10 kpc) controlling globular clusters (GC) orbital evolution, and the small-scale dynamics (sub-pc-AU) controlling the internal GC dynamics are essential for a detailed investigation of the co-evolution of GC systems (GCS) in galaxies. We introduced a novel method for the simultaneous evolution of large GCS that combines fully self-consistent Monte Carlo MOCCA models with semi-analytic GCS models. In order to reproduce the observable features of GCs in the Milky Way and Andromeda, we generated synthetic GC populations using the population synthesis code MASinGa and the MOCCA-Survey Database I. In this study, an attempt was made to determine constraints to the spatial distribution of GCs in both galaxies and the contribution of GC to the formation of the nuclear star cluster and supermassive black holes. Additionally, the black hole and black hole-black hole binaries populations in globular clusters in these galaxies have been studied


"Imaging X-ray Polarimetry Explorer (IXPE) satellite-based mission: instruments, observations, and synergy with other missions"

Grzegorz Madejski (Stanford University and SLAC National Accelerator Center, Stanford, California)

Imaging X-ray Polarimetry Explorer (IXPE) is an international, NASA-led satellite-based mission designed to study polarization of celestial sources in X-ray band, over a bandpass of 2 - 8 keV. The payload, launched in December 2021, consists of three telescopes (built at NASA's Marshall Space Flight Center) focussing X-rays onto polarization-sensitive imaging detectors (built at INFN / Pisa, Italy). This presentation will provide an overview of the mission, and will highlight several early IXPE observations, where the detection (or sensitive non-detection) provides important constraints on the emission processes as well as geometry of celestial X-ray emitters. It will also highlight the synergy of IXPE observations with the data obtained in other wavelengths besides soft X-rays.


"Massive neutron stars observations and theory of dense nuclear matter"

Leszek Zdunik (CAMK, Warsaw)

Recent estimations of the mass of neutron stars indicate that the maximum mass of such objects could be significantly larger (even by about 20%) than the value which appeared to be well established for the last 10 years (two solar masses). I will discuss the possible consequences of such measurements for the properties of dense nuclear matter.


"Accretion disk backflow in resistive MHD simulations"

Ruchi Mishra (CAMK, Warsaw)

Backflow is a part of the flow in the accretion disk which is directed away from the star. Although it is well established in purely hydro-dynamical framework, it is only recently that it has been identified in magnetohydrodynamics (MHD) simulations. We perform resistive magnetohydrodynamics (MHD) simulations of an accretion disk with alpha-viscosity, accreting onto a slowly rotating star endowed with a magnetic dipole. We find backflow in the disk-midplane for a range of conditions when the Prandtl number is less than a critical value. Close to the critical Prandtl number value the backflow shows non-stationary behavior. We compare the results with hydrodynamics simulations. We find that in the MHD case the distance from the star at which backflow begins, the stagnation radius, is different than in the hydrodynamic case.