Wednesday Colloquium


"Transitional millisecond pulsars"

Alessandro Papitto (Osservatorio Astronomico di Roma)

Millisecond pulsars are the quickest spinning compact objects known and hence the best probes to measure the state of ultradense matter and test the theory of General Relativity. They attain their very fast rotation during a Gyr-long phase of accretion of matter from a low mass companion star, which drives a bright X-ray emission. When the mass transfer stops magnetospheric pulsed emission powered by the star rotation - and observed preferentially in the radio and gamma-ray bands - sets in. This complex evolution has been recently demonstrated by the discovery of transitional millisecond pulsars (Papitto et al. 2013, Nature) that swing between an accretion-powered X-ray pulsar regime and a rotationally-powered radio pulsar state on a time scale of a few weeks, or even shorter. These pulsars show an incredibly rich phenomenology that reflects all the possible outcomes of the interaction between the pulsar wind of particles and radiation and matter in an accretion disk. This has been confirmed by the discovery of optical pulsations from a transitional pulsar (Ambrosino, Papitto et al., 2017, Nature Astronomy), the first ever from a millisecond spinning neutron star. The pulsations were observed by using the fast photometer SiFAP at the INAF Galileo Telescope. Optical pulses were detected when the pulsar was surrounded by an accretion disk, but they are most likely originated by a rotation-powered magnetospheric process. The profound implications for our understanding of the pulsar disk/magnetosphere interaction will be discussed.


"Tidally induced morphology of M33 in hydrodynamical simulations of its recent interaction with M31"

Marcin Semczuk (NCAC, Warsaw)

Milky Way, M31 and M33 are the three largest galaxies in the Local Group. M31 and M33 create a somewhat separated pair, with their relative distance being ~4 times smaller than the distance to the Milky Way. Except for their proximity, there are several other traits suggesting that the two galaxies interacted in the past. M33 has a warped gaseous and stellar disks that might have a tidal origin and both galaxies exhibited a rapid increase in their star formation rates at around 2 Gyr ago. During the seminar, I will discuss arguments for and against the possible past interaction between M33 and M31 and I will present our recent results on our attempt to simulate the recent history of the system.


"Holocene climatic fluctuations (so-called Bond or RCC events) in the light of geoarcheological and astronomical data"

Fabian Welc (Institute of Archaeology, UKSW, Warszawa)

Just two decades ago, Holocne was considered as relatively climatically stable period, but recent, reseach revealed extremely dynamic climate fluctuations which took place during last 10,000 years. These sudden and catastrophic climate fluctuations are referred to as Rapid Climatic Changes (RCC) or Bond events. They represented eight cold oscillations that took place every 1500 years. Bond or RCC events contributed to significant environmental changes in various parts of the world (especially on the northern hemisphere) and exerted an overwhelming influence on the development and disappearance of the past ancient cultures and civilisations. Until now, it is not known what triggers RCC events. One of the most acceptable concepts is the impact of astronomical factors such as changes in earth's orbit parameters and value of insolation. Today there is no doubt that past cultures have developed in accordance with the rhythm of climate change, but this issue has only been subject to insightful multidisciplinary research for last several years. The main subject of the presentation will focus on rapid climate oscillations related to the Bond events no. 5 (8.2 ka BP), 3 (4,2 ka BP) and 1 (1.5 ka BP), because they have had a significant, even catastrophic impact on ancient civilizations.