Wednesday Colloquium


"Quantum principle of relativity"

Andrzej Dragan (Institute of Theoretical Physics, Warsaw University and National University of Singapore)

We show that the local and deterministic mode of description is not only in conflict with the quantum theory, but also with relativity. We argue that elementary relativistic properties of spacetime lead to the emergence of a non-deterministic quantum-mechanical picture involving quantum superpositions and complex probability amplitudes.


"GWTC-3 and the origin of gravitational wave sources"

Tomasz Bulik (CAMK, AstroCent, UW, Warsaw)

The recent catalogue of gravitational wave sources GWTC-3 provided a wealth of information on the properties of merging binaries that already allow some statistical studies. I will summarize these information. I will then proceed to models of formation of these objects and present their properties. Finally, I will confront the two and discuss the viable options for formation of merging binaries observed in gravitational waves.


"Using classical Cepheids to study the far side of the Milky Way disk"

Javier Minniti (CAMK, Warsaw)

Classical Cepheids (CCs) are among the most useful Galactic and nearby extragalactic distance tracers because of their well-defined period-luminosity relations. Moreover they are young and luminous stars, with characteristic light variations that make them - relatively - easy identifiable. For these reasons, they are excellent standard candles and ideal tracers of the Galactic disk. Their location at the Milky Way disk complicates their identification, mainly due to the substantial reddening they are subject to. This can be surpassed through the use of infrared (IR) photometry. Using data from the Vista Variables in the Vía Láctea (VVV) Survey we are now able to study these young standard candles in highly reddened regions of our Galaxy that were previously hidden to us. However, the classification based solely on near-IR light curves has proven difficult, and prone to providing highly contaminated samples. In this talk, I will show how the use of additional observable properties aids in the light-curve based classification process and present two different approaches to obtain clean samples of CCs: (1) Using spectroscopic follow-up data for a sample of CC candidates. (2) Using proper motion information obtained from the VVV survey. We have been able to significantly increase the number of bona fide CCs at the far disk using near-IR photometric and spectroscopic data. The obtained samples will be used to characterize the properties of the far Galactic disk.


"Global radiative 3D GRMHD models of geometrically thin strongly magnetized disks"

Bhupendra Mishra (Los Alamos National Lab, New Mexico US)

The radiation pressure supported standard accretion disk model (Shakura Sunyaev 1973 model) is prone to classical thermal and viscous instabilities. However, these instabilities are not observed in astrophysical systems as disks remain thermally stable for astronomical time periods. In this talk, I will show some of the key findings of strongly magnetized accretion disks simulated using 3D global radiative GRMHD simulations. We used a set of initial magnetic field configurations to produce an enhanced magnetic field amplification and hence stabilize the radiation pressure dominated accretion flows around stellar mass black holes. We also found that despite the magnetic pressure support, the luminosity and mass accretion rates do match with what is expected from a standard accretion disk model.

The Colloquium will start at 4:15 pm