Wednesday Colloquium


"Massive black holes in the cosmos"

Marta Volonteri (Institut d'Astrophysique de Paris)

Massive black holes weighing from a few thousands to tens of billions of solar masses inhabit the centers of today’s galaxies, including our own Milky Way. Massive black holes also shone as quasars in the past, with the earliest detected a mere one billion years after the Big Bang. Massive black holes during their cosmic evolution interact with diverse environments, starting from messy and rapidly evolving galaxies at high redshift to quiescent galaxies today. I will discuss how these changing environments affect the growth of massive black holes and the formation of massive black hole binaries.


"X-ray spectral and timing studies of ultraluminous X-ray sources."

SAMARESH MONDAL (সমরেশ) (CAMK, Warsaw)

Ultraluminous X-ray sources (ULXs) are off-center point sources with assumed isotropic X-ray luminosity above 10^39 erg/s. Now it is commonly considered that most ULXs have a stellar-mass BH or a NS after the discoveries of several pulsating ULXs. Therefore the luminosity indicates accretion above the Eddington limit. We find various observational signatures of super-Eddington accretion imprinted onto the X-ray observations. In my talk, I will briefly discuss the X-ray spectral and timing properties of these sources and compare them with Galactic X-ray binaries or AGNs.


"High-Amplitude Delta Scuti stars"

Henryka Netzel (CAMK, Warsaw)

High-Amplitude Delta Scuti stars (HADS) is a subgroup of Delta Scuti stars which is characterized by high-amplitude pulsations, typically in radial modes. I studied Delta Scuti stars from the Galactic bulge using the OGLE photometry and selected candidates for HADS pulsating in multiple radial modes. I performed seismic modeling of these selected multi-mode HADS in order to constrain their physical parameters. I will show results of the search for HADS among Delta Scuti stars in the Galactic bulge, their inferred physical parameters based on theoretical models and their properties.


"A shoebox-sized simulator of the antique Cosmos: The ancient Greek Antikythera Mechanism"

Dietrich Baade (ESO Garching)

In 1901, the heavily corroded remains of a strange object were found in an ancient shipwreck. The details of its inner workings remained enigmatic for a century. X-ray tomography obtained a century later and masterly reverse engineering led to a comprehensive reconstruction of its functionality. The result reveals that the mechanism incorporated all Babylonian and Greek astronomical knowledge of its time with an amazing precision. It is the first time machine and analog computer. Its mechanical realization is the work of a genius. The congenial combination of scientific and technical brilliance makes the Antikythera mechanism the most remarkable scientific-technical project of all times. The talk will give an overview of the astonishing diversity of functions and how it was finally possible to decipher them.