Wednesday Colloquium


"First Light And Reionization Explorer"

Denis Burgarella (Laboratoire d'Astrophysique de Marseille)

There has been enormous progress over the past decade in finding galaxies which existed early in the history of the Universe (within a billion years of the Big Bang, at z > 6). The next few years will see the “high redshift frontier” pushed even further with the JWST and ground-based ELTs. However, the limited field of view of these facilities, and sensitivity only out to the near-infrared (λ<2μm) for the WFIRST and Euclid wide-field imaging space missions, mean that a crucial piece of the jigsaw remains missing: a wide-field imaging survey, working at mid-infrared wavelengths (necessarily from space) is needed to find the most massive and luminous galaxies at the highest redshifts, the progenitors of which are likely to be the first galactic structures to form. We propose FLARE (First Light And Reionization Explorer), a space mission to study galaxy evolution at the earliest times, with the key goals of detecting a statistically significant (> 100 at z = 14) sample of first galaxies. FLARE is a space mission whose primary goal (~70% of lifetime) will be to identify and study the universe before the end of the reionization at z > 6, detect, identify and study “first light” galaxies at dawn of time (13 < z < 15). A secondary objective (~25% of lifetime) is to survey star formation in the Milky Way and build a 5000 deg2 survey in the Milky Way. More information:


"Dynamics of topological excitations: from ultracold atomic gases to atomic nuclei and neutron stars"

Piotr Magierski (Faculty of Physics, Warsaw University of Technology)

Superfluidity and superconductivity are remarkable manifestations of quantum coherence at a macroscopic scale. The existence of superfluidity has been experimentally confirmed in a large number of systems: in various condensed matter systems, in nuclear systems including nuclei and neutron stars, in both fermionic and bosonic cold atoms in traps, and it is also predicted to show up in dense quark matter. Surprisingly the superfluid properties of many of these systems are qualitatively similar, and in particular various topological excitations can be observed in the form of vortices or solitons, leading possibly also to the quantum turbulent state. From the theoretical perspective dynamics of Fermi superfluids is quite complex and thus requires a suitable theoretical framework, which is provided by time-dependent density functional theory (TDDFT). TDDFT can be viewed as an exact reformulation of time-dependent quantum mechanical problem, where the fundamental variable is density instead of the many-body wave-function. During the lecture I will present various features related to dynamics of topological excitations in ultracold atomic gases (vortex reconnections, solitonic cascades), atomic nuclei (solitonic excitations in nuclear collisions) and neutron stars (vortex-impurity interaction in the crust).


" Are we seeing a new type of accretion disk around transitional pulsars?"

Alessandro Patruno (Leiden University)

Accretion disks in X-ray binaries (and cataclysmic variables) show a plethora of phenomena and it is in general difficult to understand the general principles that govern them. A good practice is to distinguish the properties common to several systems and those which are instead unique to specific systems. In this talk I will discuss some unique and still unexplained characteristics of accretion disks seen in the so-called transitional millisecond pulsars. These objects are neutron stars (with a low mass companion) that turn back and forth between a radio pulsar state and an accreting pulsar state. During the accretion process, the X-ray lightcurves (and also their radio and gamma ray behaviour) seems to be very different from those of other low mass X-ray binaries. What might causing such difference is still an open question. I will present some recent results of multiwavelength campaigns and focus on the geometry and observational constraints that can be placed on these systems.


"Stellar clusters, supernovae and the Sun"

Melvyn Davies (Lund Observatory)

Most stars form in some sort of cluster or association. These birth places are harsh environments. Massive, bright stars accelerate the photoevaporation of protoplanetary disks whilst other close encounters can destabilize pre-existing planetary systems. In this talk I will explain why it is thought that the Sun formed in a stellar cluster. I will discuss the consequences for our own Solar System and identify M67 as one possible host cluster.