Seminars
Our seminars take place in the library of the Main Building (Praha–Sporilov, see
Contacts).
Scheduled:
26.10.2009 14:30
Ulf Torkelsson
Chalmers University of Technology and Goteborg University, Sweden
Accretion discs around magnetized neutron stars
Abstract
Ulf Torkelsson
Accretion discs around magnetized neutron stars
Ghosh & Lamb constructed the standard model for an accretion disc around a magnetic star in 1979. The dipole field of the star produces a toroidal magnetic field in the disc because of the mismatch between the rotation of the star and the Keplerian rotation in the disc. The resulting magnetic tension is then responsible for an exchange of angular momentum between the star and the disc. Since then, through the work by Balbus & Hawley, we have become aware of that the accretion disc can produce a magnetic field on its own. This magnetic field can significantly enhance the torque between accretion disc and the neutron star. Furthermore the torque reversals that have been observed in disc-accreting X-ray pulsars by Bildsten and co-workers can then be interpreted as reversals of the magnetic field in the accretion disc. Belay Tessema and Torkelsson have recently produced self-consistent models of such accretion discs.
01.01.2010 14:00
Fernando de Felice
University of Padova, Italy
Why dark matter is
dark?
Abstract
Fernando de Felice
Why dark matter is dark?
Introducing the concepts of space- and time-velocities we can formulate a Generalized Principle of Relativity which states that any particle has a world-velocity equal to the Maxwell's constant c with respect to any observer. We propose that dark matter has time-velocity equal to zero and discuss the possible implications.
Previous:
01.10.2009 14:00
Marek Abramowicz
Goteborg University, Sweden, and N. Copernicus Astronomical Center, Warsaw, Poland
The black hole accretion
Abstract
Marek Abramowicz
The black hole accretion
I will describe the main results of the theory of black hole accretion. A fairly complete description includes all classical results. Namely: the Balbus-Hawley theory of turbulent stresses; the Shakura-Sunyaev accretion disc; Polish doughnuts, ion tori, slim discs, and the `adafs'; disco-seismology and the Papaloizou-Pringle instability — as well as recent developments in calculating spectra by advanced ray-tracing. I do not assume any detailed knowledge of general relativity or radiative processes. I will introduce all the necessary physics step by step, in a way that (I hope) will be helpful for beginners and not boring for experts.
This is the first lecture in the series of six, scheduled to be presented during autumn 2009.
We try hard to meet regularly to discuss ongoing research projects and recent astro-ph papers.
If you would like to give a seminar in our group, please contact Vladimir Karas.
Everybody is welcome.
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