Séminaires

Strong lensing of gravitational waves, results and challenges
Justin Janquart (Universiteit Utrecht)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

Like electromagnetic signals, gravitational waves can undergo gravitational lensing when a massive object (e.g. galaxy or galaxy cluster) is present on the path from source to observer. For gravitational waves, lensing manifests itself as repeated events with the same frequency evolution but magnified, phase-shifted, and arriving at different times. Depending on the lens, the time delay can go from seconds to months. According to current forecasts, there are real chances of observing lensing in the Advanced LIGO and Advanced Virgo in the coming years. Computationally, finding lensed events is a real challenge as one needs to analyze all the event pairs present in the data, and more when accounting for sub-threshold events. Additionally, there is a serious risk of false claims as events can resemble each other by chance. Here, we start by presenting some search techniques and avenues to address challenges related to the detection of strong lensing. Then, we present the most recent results from the LIGO-Vigo-KAGRA collaboration. We conclude by outlining the perspective for gravitational wave lensing with possible applications.

A Collage of Exoplanets on the Mass-Radius Diagram
Ji Wang (Ohio State University)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

I will talk about different populations of exoplanets and their interconnection. Specifically, I will present chemical composition measurements for hot Jupiters and directly-imaged young jovian planets, in an attempt to answer questions such as how stellar chemical composition controls the planet formation; how the difference of planetary and stellar chemical abundance reveals the history of orbital migration. In addition, I will highlight the recent progress in comparative planetology by contrasting (1) small planets with different densities and structures; and (2) Earth-size rocky planets vs. gas dwarf planets in the habitable zone. These comparative studies shed light on the origin of the diverse outcome of planet formation and the search for biosignatures with current and future facilities.