Wednesday Colloquium


"Quasars and dark energy"

Bożena Czerny (Center for Theoretical Physics and CAMK, Warsaw)

Dark energy can be studied with a number of probes, broadly classified as standard candles and standard rulers. The use of several independent probes is needed to get accurate and reliable results since every probe has its particular systematic problems/biases. Quasars do not seem to be obvious standard candles but there are two ways to pursue. The first method is based on the selection of special sub-class of quasars, which radiate precisely at Eddington ratio. The second method can use all quasars, but requires to perform the monitoring of the quasar variability of the continuum and of the emission lines. Reverberation studies (i.e. the measurements of the time delay of the line emission with respect to the continuum) allow to establish the absolute monochromatic luminosity of a given source independently of its redshift. We developed a theory which explains the delay-luminosity relation known for nearby sources and allows to extrapolate this type of relation towards higher black hole mass sources, like quasars at redshifts of a few. Preliminary studies are being done using our data from the dedicated campaign with the 11-m SALT telescope. These high-quality data allow to study the spectra in much detail (including the spectra decomposition into lines and Fe II pseudo-continuum) in order to determine the possible systematic errors. Later the method will be applied to expected spectroscopic surveys; in addition, current estimates indicate that the project can also be undertaken with a photometric survey of the quality of LSST. The advantage of using quasars lies in their broad range of redshifts, large number of available sources and weak evolution of their metallicity with redshift.


"High-resolution radio view of the AGN jets and their magnetic fields"

Tuomas Savolainen (Aalto University Metsähovi Radio Observatory, Kylmälä )

Understanding the mechanisms for launching, accelerating, and collimating the magnetized jets of plasma from accreting black holes is one of the central questions in relativistic astrophysics. During the past decade significant progress has been made in the theoretical description of the jet formation, and especially in the field of complex general relativistic magnetohydrodynamic simulations. High-resolution radio imaging of (sub-)parsec-scale structures in the jets, especially in polarization, is one of the very few ways to derive observational constraints for the physical conditions in the jets in or close to their acceleration and collimation site, and thus place constraints on the theory. In this talk I will discuss recent results from the state-of-the-art very long baseline interferometry observations regarding the jet magnetic field structure, acceleration/collimation of the flow, and the conditions near the black hole itself.


"The Polish doughnut revisited"

Marek Abramowicz (NCAC, Warsaw)


"Arachne’s fate. On textile production in Bronze Age Greece and craft research in academia"

Agata Ulanowska (The Institute of Archaeology, Department of History, Warsaw University)