Wednesday Colloquium


"Hydrogen Burning White Dwarfs and their Mysterious Short Pulsations in X-Rays"

Marina Orio (Department of Astronomy, University of Wisconsin/INAF - Astronomical Observatory Padova)

Luminous supersoft X-ray sources are usually white dwarfs (WDs) undergoing shell burning in a thin layer at the bottom of an envelope accreted from an interacting binary companion (either a main sequence or a red giant star). The vast majority are in post-outburst novae that continue thermonuclear burning for a period varying from days to years, but also a few steady or recurrent non-nova burning WDs have been discovered. Several of them are in symbiotics and a few are in massive binaries, with a Be companion. In a number of novae after the outburst, and in the non-nova binaries CAL 83 of the LMC and "r3-8" of M31, short pulsations of the X-ray flux with periods around one minute have been discovered. These were initially proposed to be non-radial oscillations caused by the shell burning, as observed in some AGB stars (so called "epsilon mechanism"), however recent work shows that effective temperature and other WD parameters are not consistent with the observed times for such a mechanism. In recent work on Nova LMC 2009 and on CAL 83, we discovered that the period of the oscillations drifts by a few percent during time scales of hours, and even the pulsation amplitude varies. I will show the data and discuss possible interpretations for this puzzling phenomenon of time variability, and what it may imply for the evolution of white dwarf binaries.


"Unified equation of state consistent with astrophysical, gravitational, high- and low- energy nuclear physics data and its applications"

Violetta Sagun (Coimbra University)

I will present a novel equation of state, which includes the surface tension contribution induced by the interparticle interaction and the asymmetry between neutrons and protons, to the study of neutron star properties. This equation of state is obtained from the virial expansion for the multicomponent particle mixtures that takes into account the hard-core repulsion between them. The considered model is in full concordance with all the known properties of normal nuclear matter, provides a high quality description of the proton flow constraints, hadron multiplicities created during the nuclear-nuclear collision experiments and equally is consistent with astrophysical data coming from neutron star observations and GW170817 merger. I will show how the induced surface tension (IST) equation of state opens an elegant way to describe the properties of matter across a very wide range of densities and temperatures. In the second part of the presentation I am going to present our recent results of an impact of asymmetric dark matter on properties of the neutron stars and their ability to reach the two solar masses limit. It allows us to present a new upper constraint on the mass of dark matter particle. Our analysis is based on the observational fact of existence of three pulsars reaching this limit and on the theoretically predicted reduction of the neutron star maximal mass caused by accumulation of dark matter in its interior.


"What was the last Nobel Prize in Physics given for?"

Ewa Łokas, Maciej Konacki (NCAC, Warsaw)