Wednesday Colloquium



Arkadiusz Orłowski (The Faculty of Applied Informatics and Mathematics, Warsaw University of Life Sciences (SGGW))


"Radiation pressure on disks: avalanches and instabilities"

Paweł Artymowicz (Physical Sciences, University of Toronto)

The bulk of gas in gas-and-dust disks of young planetary systems disappears about 10 million years. However, even systems as old as the solar system feature observable disks of dust derived from collisions and evaporation of planetesimals. Beta Pictoris, Fomalhaut, AU Mic, and other stars have prominent dusty disks with nontrivial, resolved nonaxisymmetric morphology. Planets are one possible explanation, but there are also dust+gas+radiation effect which can mimic the action of planets and produce somewhat similar effects. Avalanches of dust can develop in disks and limit the dustiness of circumstellar disks with small gas contents. A newly discovered radiation pressure instability involves nothing else than the radiation pressure from the central object. It produces growing nonaxisymmetric modes in optically thick inner parts of the disk, which in the nonlinear regime transform into numerous vortices at first, coalescing into a few larger ones in the end. Linear theory predicts very well well the numerically determined growth rates of these modes. Breaking of the initial axial symmetry and the production of spiral and vortical structure can occur in a wide class of optically thick astrophysical disks, for instance in accretion disks around compact objects.


"Thermal and rotational evolution of neutron stars"

Morgane Fortin (NCAC, Warsaw and Laboratoire Univers et Théories, Paris-Meudon Observatory)

I will discuss the modelling of two aspects of the evolution of neutron stars. On the one hand, I will focus on the thermal evolution of isolated and accreting neutron stars. Its modelling requires the precise description of the microphysics inside neutron stars, in particular the composition and superfluid properties. X-ray observations provide us with surface temperature measurements and enable to probe the properties of the interior of neutron stars. On the other hand, I will discuss the rotational evolution of neutron stars, in particular of millisecond pulsars. These are rapidly rotating neutron stars with a lower-than-average magnetic field. They are in fact old pulsars that have been revived by the accretion of matter from a companion star. This process has led to the decay of their magnetic field. I will report a new modelling of this process, that, together with evolutionary constraints, allows to estimate the properties of the progenitor neutron star of currently observed millisecond pulsars.


"Role of unconventional natural gas production in Poland and other European countries"

Jan Winter (Polish Oil and Gas Company (PGNiG), Warsaw)

Scope of presentation: 1. Polish Gas Market issues and corporate profile of Polish Oil and Gas Company (POGC) 2. European and Polish energy policy vs a number of benefits from a new unconventional gas production 3. Definitions of unconventional natural gas production ( shale gas, calbed methane gas, tight gas, hydrates gas ) 4. Resources (reserves) of conventional and unconventional natural gas in Poland and elsewhere 5. Economic, financial, technical and environmental issues dealing with unconventional natural gas extraction 6. Golden Rules for a Golden Age of Gas* 7. Some comments and Discussion