Wednesday Colloquium


"Simulating ULXs: super-Eddington accretion onto magnetized neutron stars"

David Abarca (CAMK, Warsaw)

Observations of ultraluminous X-ray sources (ULXs) paired with coherent pulsations have shown that accreting neutron stars are capable of emitting super-Eddington emission. We run general relativistic radiation magnetohydrodynamic simulations of super-Eddington accretion onto magnetized and non-magnetized neutron stars. We show how the combination of an approximately ten billion Gauss stellar magnetic field, the hard surface of the neutron star crust, and collimation from the outflowing gas produce apparent luminosities in excess of 200 times the Eddington limit which is well in the range of observed neutron star ULXs


"Gravitational Lensing in Simulated Images of Black Holes"

Zachary Gelles (Harvard University)

In 2019, the Event Horizon Telescope published the first image of a black hole, paving the way for future efforts to improve our understanding of emission around compact objects. However, many of the most prominent and unexpected effects of black holes on their images are only visible at extremely fine resolutions. To analyze these features, I will describe an approach to adaptive ray-tracing that allows us to efficiently generate high-resolution images of black holes by concentrating rays near sharp features of the image. I will present examples that provide key insights into the turbulent accretion flow and photon ring. In addition to the imprint of the spacetime via gravitational lensing of the total intensity, black holes also impart distinctive features on polarized emission. I will describe efforts to understand polarimetric images of black holes using simplified, semianalytic models of synchrotron emission near black holes, and I will discuss the effects of spin, magnetic field, and inclination angle on the observed polarization. Together, these tools provide insight into the role that black hole imaging might play in understanding the supermassive black holes at the centers of galaxies. I will specifically make comparisons to previous imaging efforts of the Galactic Center supermassive black hole, Sgr A*, and I will discuss the role of these tools in enabling future endeavors in Space VLBI.

due to the time difference the talk will start at 3:15 pm Warsaw time.


"Heat, work and temperature in special relativity"

Lorenzo Gavassino (CAMK, Warsaw)

Heat, work and temperature are probably some of the most elusive concepts of physics. Although we all seem to agree on the intuitive concept underlying these thermodynamic entities, their fundamental meaning in a relativistic context seems to be still under discussion. A fully covariant formulation of the laws of thermodynamics requires that we first put an end to these controversies.


"Exploration of faint parts of bright galaxies in the MATLAS survey"

Michal Bílek (Observatoire astronomique de Strasbourg)

The purpose of this talk will be to introduce myself and present our latest work on the MATLAS survey. MATLAS took very deep optical images of around 200 nearly elliptical and lenticular galaxies to explore very faint structures in the galaxies or their vicinity. Most importantly, the images captured tidal features, the remnants of past galaxy interactions. This will help us to address the role of mergers in the assembly of our galaxies.