Seminars
Our seminars take place in the lecture room of the building at
Praha–Sporilov.
Next seminar:
21.09.2015 09:30
Jaroslav Hamersky
Astronomical Institute, Academy of Sciences, Prague
Astrophysical processes near a galactic centre
Abstract
Jaroslav Hamersky
Astrophysical processes near a galactic centre
An accretion torus is an important astrophysical phenomenon which is believed to account for various features of mass inflow and release of radiation on diverse scales near stellar-mass as well as supermassive black holes. When the stationary torus is perturbed it starts to oscillate and once some part of the torus overflows the closed equipotential surface, defined by the stationary solution, this material is accreted or ejected. These oscillations reveal both spacetime properties and the intrinsic characteristics of the torus model. We study the oscillation and accretion properties of geometrically thick accretion tori using general relativistic magnetohydrodynamic simulations. Assuming axial symmetry these simulations are restricted to 2-D approximation. We discuss the impact of the presence of the large scale magnetic field and the profile of the specific angular momentum on the oscillation properties and on the accretion flow motion.
21.09.2015 11:00
Michal Bilek
Astronomical Institute, Academy of Sciences, Prague
Galaxy interactions: dark matter vs. Modified Newtonian dynamics (MOND)
Abstract
Michal Bilek
Galaxy interactions: dark matter vs. Modified Newtonian dynamics (MOND)
MOND is an observational rule for predicting the acceleration of stars and galaxies from the distribution of the visible matter. It possibly stems from a new law of physics. I list the theoretical aspects of MOND, its achievements and problems. MOND has been tested mainly in disc galaxies so far. Its tests in elliptical galaxies are rare because the MOND effects are small for them in the parts observable by the conventional methods. In the thesis, I explain the methods and ideas I developed for testing MOND in the ellipticals using stellar shells. Moreover, the shells enable us to test MOND for stars in radial orbits for the first time. The shells are results of galactic interactions. I discuss the shell formation mechanisms and summarize the findings from shell observations and simulations.
22.09.2015 15:00
Agnieszka Janiuk
Center for Theoretical Physics, Polish Academy of Sciences, Warsaw
Activity of supermassive black holes
Abstract
Agnieszka Janiuk
Activity of supermassive black holes
On the cosmological scale, evolution of the Universe is much affected by the presence of supermassive black holes. One of the interesting issues is the intermittent character of their activity in the host galaxies, and the so-called duty cycles. On the other hand, a large fraction of SMBHs must have passed through the phase of a merger. In this context, the effects of BH spin reorientation as well as the signatures of gravitational recoil effect have been observed in a number of distant quasars. Thus the understanding of black hole growth, their feedback with galaxy formation and evolution, and the timescale of accretion before and after the mergers, are key questions that link the BH astrophysics and cosmology. In my talk, I will review the recent observational and theoretical developments in this topic.
Previous seminar:
10.08.2015 15:00
Norbert Werner
Kavli Institute for Particle Astrophysics and Cosmology, Stanford University
How supermassive black holes and star-formation sculpt the visible Universe
Abstract
Norbert Werner
How supermassive black holes and star-formation sculpt the visible Universe
In the course of structure formation, only a small fraction of the baryons turned into stars - most remain in a diffuse intergalactic medium. The growth of galaxies is regulated by feedback processes, such as energy and momentum input from supernovae, and jets and winds of accreting supermassive black holes. These processes, collectively called galactic feedback, can limit or even inhibit star formation, and thus a detailed knowledge of how they work is essential for our understanding of galaxy formation and evolution. I will start my talk by presenting recent observational results on the role of supermassive black holes in keeping the most massive galaxies 'red and dead'. Then, I will 'zoom out' to the outskirts of galaxy clusters where we also find hints that supermassive black holes played an important role in the distant past. X-ray observations with the Suzaku satellite reveal a remarkably homogeneous distribution of iron out to the virial radius of the nearby Perseus Cluster, requiring that most of the metal enrichment of the intergalactic medium occurred before the cluster formed, probably more than ten billion years ago, during the period of maximal star formation and black hole activity. Finally, I will talk about the upcoming ASTRO-H satellite which will revolutionize X-ray spectroscopy and our understanding of how feedback processes couple to the intergalactic medium.
If you would like to give a seminar in our group, please contact Vladimir Karas or Jaroslav Hamersky.
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