Seminars at the Institute of Physics are recorded and available to the public online on our youtube channel.
A full list of all Seminars that took place at the Institute can be found on our website.
This seminar was given in two parts.
Author: Adolfo Cisterna
Date: 26. 7. 2022
Location: Opava
Part 1
Part 1
This Seminar was given in three parts.
Author: Mikulas Gintner
Date: 22. 07. 2022
Location: Opava
Author: Sudipta Hensh
Date: 28. 07. 2022
Location: Online
Author: Elena Kopteva
Date: 4. 8. 2022
Location: Opava
Author: Prof. Naresh Dadich
Date: 12. – 15. 6. 2022
Location: Opava
This series of seminars was given in four parts over four days.
Title: Gravitational self interaction and light’s interaction with gravity
Short description: The first of the four lectures of Prof. Dr. Naresh Dadhich during his visit to the Institute of Physics in Opava in June 2022. General Relativity is derived in the most direct and compelling way based on simple common sense considerations. It is shown how the two new aspects, gravitational self interaction and light’s interaction with gravity, take care of each-other so beautifully leaving the Newton’s inverse square law intact.
Title: True constant of spacetime structure
Short description: The second of the four lectures of Prof. Dr. Naresh Dadhich during his visit to the Institute of Physics in Opava in June 2022. The Lambda constant is introduced as a true constant of spacetime structure on the same footing as the velocity of light, and it has nothing to do with the vacuum energy. Einstein’s equation of gravitation is not prescribed;instead it is mandated by the geometry of the Riemannian spacetime manifold, so much so that the inverse square law is a property of spacetime geometry. In this way we would build a new and insightful perspective of understanding GR.
Title: Solutions to the General Relativity
Short description: The third of the four lectures of Prof. Dr. Naresh Dadhich during his visit to the Institute of Physics in Opava in June 2022. Solutions to the General Relativity are obtained in the most direct and compelling way based on simple common sense considerations. Schwarzschild, Kerr, Reissner-Nordstrom, and other solutions are discussed.
Title: Extension of the GR to higher dimensions
Short description: The fourth of the four lectures of Prof. Dr. Naresh Dadhich during his visit to the Institute of Physics in Opava in June 2022. Extension of the GR to higher dimensions, the necessity of such extensions, and the properties of the new solutions are introduced. The roles of fundamental forces, their interconnections, and perspectives of their combination are discussed.
Author: Odele Straub
Date: 16. 06. 2022
Location: Online
Author: Prof. Luigi Stella
Date: 23. 06. 2022
Location: Online
Author: Fréderic Vincent
Date: 19. 05. 2022
Location: Online
Author:Deepika Bollimpalli
Date: 12. 05. 2022
Location: Online
Abstract: Long-term observations have shown that black hole X-ray binaries exhibit strong, aperiodic variability on time scales of a few milliseconds to seconds. In addition, these systems also exhibit rapid variability in their X-ray light curves termed quasi-periodic oscillations (QPOs); also broadly classified into high-frequency and low-frequency QPOs. Understanding the nature of these variabilities and the underlying physical processes helps us probe the nature of the compact object and its surroundings. In this talk, I shall give a broad overview of the existing theoretical models for broadband variability and different types of QPOs, with a focus on the findings from the current state-of-art simulations of accretion discs in reproducing such time variability phenomena. In particular, I will discuss how the mass accretion rate fluctuations generated by the turbulence in the simulations naturally explain the observed broad-band variability in BHXRBs, and how the precession frequency of the inner geometrically thick disc differs from the standard Lense-Thirring precession frequency in truncated disc geometry and its implications to Type-C QPOs.
Author: David Abarca
Date: 17. 02. 2021
Location: Online
Author: Maciek Wielgus
Date: 24. 04. 2021
Location: Online
Author: Bhupendra Mishra
Date: 10. 05. 2021
Location: Online
Abstract: Whenever an unfortunate star gets too close to a black hole, it starts to accrete into the black hole. The accreting star also carries its own little magnetic field with it. Now what happens to this magnetic field? Does it play a key role in shaping the accretion flow? In this talk, I shall present first ever attempted three dimensional global GRMHD simulations to shed light on the effects of magnetic field configurations onto the dynamics of accretion flows. Based on this study, I will be advocating for a need for a strong magnetic field in theoretical models to explain several observational features of accreting black holes. Additionally, I will talk about how nature could produce the required strong magnetic field without artificially injecting it in our models. I will conclude the presentation with one of the most interesting features of time variability originating due to the GR effects of the black hole. This time variability is observed in X-ray emission from accretion disks and remains fixed for a given system. Using a series of numerical simulations, I will give a theoretical explanation of what could cause such a harmony in one of the most energetic and complex systems.
Author: Zachary Gelles (Harvard University)
Date: 10. 06. 2021
Author: Maciek Wielgus (Black Hole Initiative, Harvard University, USA)
Date: 27. 02. 2020
Location: Opava
Abstract: The Event Horizon Telescope (EHT) has delivered first resolved images of M87*, a supermassive black hole in the center of the M87 galaxy. These results are based on the 230 GHz observations performed in April 2017. Dedicated tools were developed to facilitate the modeling and analysis of the EHT 2017 data set in the Markov chain Monte Carlo (MCMC) framework, demonstrating that the source morphology can be very well represented by a crescent. More data, from different time epochs, are required to investigate the long term stability of the source parameters, such as its diameter and orientation. To address that need, we analyze archival data from proto-EHT 230 GHz observations of M87* in the framework utilized for the 2017 data analysis. We fit geometric models to the observations taken in 2009, 2012 (published in the past) and 2011, 2013 (not published previously), exploring the parameter space with a MCMC algorithm. We validate the procedure using synthetic data and M87* source models derived from the 2017 data. While the archival data sets are far less constraining than the 2017 observations, we obtain measurements of the source diameter and orientation. Variations of the M87* morphology in the 2009–2017 period are found to be roughly consistent with the predictions of general relativistic magnetohydrodynamic simulations of a turbulent accretion flow.
