Wednesday Colloquium


"Discovery of a new class of pulsating stars"

Paweł Pietrukowicz (Astronomical Observatory, Warsaw University)

Thousands of pulsating stars have been detected in the Milky Way and other galaxies of the Local Group over the last decades mainly thanks to large-scale variability surveys. It seemed that all types of pulsating stars had been recognized. By monitoring about one billion stars in the sky, the OGLE survey has discovered extremely rare, short-period objects whose properties do not fit to any class of known pulsators. Theory shows that the newly discovered objects are evolved low-mass stars with a giant-like structure, but their origin remains a mystery.


"A simple approach to gravitational wave data analysis"

Tomasz Bulik (Astronomical Observatory, Warsaw University)

The recent discovery of binary black hole coalescence by LIGO is based on a few cycles seen in a fraction of a second. I will show how the information about the binary can be inferred from the observed variation of the signal in time using only basic physical arguments.


"Tight galaxy scaling relations: a challenge to galaxy formation models "

Benoit Famaey (Observatoire Astronomique de Strasbourg)

In this talk, we review the observational evidence for an intimate connection between the baryonic surface density and the total gravitational field in galaxies. This observational fact presents a fine-tuning problem for the particle dark matter interpretation of mass discrepancies in galaxies. We show that this is the case even when taking baryonic feedback into account. On the other hand, this is naturally explained within the MOND paradigm, hypothesizing an effective breakdown of Newtonian dynamics in the extremely low acceleration regime. However, MOND clearly breaks down on scales larger than galaxies, where there is ample evidence for a new degree of freedom behaving as a collisionless fluid of particles, i.e. dark matter. Theories modifying the lagrangian of the dark matter sector to account for the baryon-dark matter connection in galaxies while preserving the predictions of LambdaCDM on the largest scales might perhaps be a promising way to reconcile these conflicting observational facts.