Wednesday Colloquium


"Overview of Dark Matter Production in Nonstandard Cosmologies with a Focus on Axions"

Jacek Ksawery Osinski (AstroCent/CAMK, Warsaw)

The Universe is typically assumed to be radiation dominated in the period preceding big bang nucleosynthesis, however we do not currently have any observational probes to confirm this. Nonstandard cosmological histories, where some other form of energy density dominates for a time, commonly arise in theories of the early Universe. These histories have important consequences for processes, such as dark matter production, occurring in that time. In this talk I will briefly review nonstandard cosmological histories and their effects on dark matter production focusing on axion dark matter.


"White Dwarf Pulsars"

David Buckley (SAAO/SALT, University of Cape Town, University of the Free State)

The 2016 discovery of the unusual nature of the detached White Dwarf – Red Dwarf binary, AR Scorpii, has led to efforts to discover more examples of such systems. In this talk I will review the multi-wavelength properties of AR Sco, a system whose luminosity is dominated by non-thermal strongly polarized emission, pulsed at the ~ 2 min spin and beat periods. In many respects the system shares characteristics of a pulsar and is powered by the spin-down of the White Dwarf. I will also present preliminary results of a simultaneous multi-wavelength campaign on AR Sco, conducted in June 2020, involved optical observations (time resolved spectroscopy and photometry) from SALT, Keck and the SAAO 1-m telescope. In addition, X-ray observations were obtained with NICER and L-band radio observations with the MeerKAT radio telescope array. These observations are used to investigate the wavelength dependence of the periodic modulations seen in AR Sco, across the E-M spectrum. Finally, I will present observational results of a second AR Sco-like system, J191213.72−441045.1, discovered in 2022, which shares many similar characteristics with AR Sco, including pulsed X-ray, optical and radio emission and is also strongly polarized.


"Copernicus’s Mathematical Astronomy in "De revolutionibus": A Very Short Introduction"

Jarosław Włodarczyk (Institute for the History of Science, PAN, Warsaw)

Nicolaus Copernicus (1473–1543) propelled one of the greatest revolution in science and his heliocentric cosmology radically changed the relationship between man and the universe. However, to prove his concept of cosmos, Copernicus had to create mathematical models of the movements of planets. He devoted five of the six books of his "De revolutionibus" (On the Revolutions, 1543) to this task. As he himself argued, “mathematics is written for mathematicians”. In my lecture I shall outline Copernicus’s mathematical astronomy and its early reception in the form of the first Copernican astronomical tables which allowed to calculate the positions of the planets for any time.



Chandra Shekhar Saraf (CAMK, Warsaw)



Yash Bhargava (Tata Institute for Fundamental Research, Bombay, India)



Amadeusz Miszuda (CAMK, Warsaw)