Ο Τομέας Αστροφυσικής, Αστρονομίας και Μηχανικής σας προσκαλεί στο σεμινάριο της Παρασκευής 06/03/2026 και ώρα 12:00μ.μ., το οποίο θα διεξαχθεί στο ΑΣΤΕΡΟΣΚΟΠΕΙΟ, στην αίθουσα διαλέξεων «ΒΑΣΙΛΗΣ ΞΑΝΘΟΠΟΥΛΟΣ».
Τίτλος: From cosmic expansion anomalies to missing baryons: exploring the mysteries of the Universe with galaxy clusters
Ομιλητής: Δρ. Κωνσταντίνος Μίγκας, (X-ray) Oort postdoctoral fellow – Leiden Observatory, the Netherlands
Περίληψη:
Galaxy clusters are excellent probes of the most crucial cosmological questions, from the (non-)uniformity of cosmic expansion to accurately tracing the large-scale structure. In the past, we have used scaling laws between multiwavelength galaxy cluster properties to robustly detect a 9% dipole variation in the local expansion rate (Hubble constant) within 800 Mpc scales. This apparent anisotropy could be attributed to a large 800 km/s coherent flow motion (bulk flow) of galaxy clusters extending to 500 Mpc. Both of these scenarios challenge LCDM at ~4-5σ in the local Universe. In this talk, I will present new, independent results derived from X-ray data of >8,000 newly discovered clusters by eROSITA, as well as new XMM-Newton and optical data, that support the existence of a cosmological anomaly, pinpointing its origin in the local (z<0.2) Universe rather than suggesting a global anisotropy. I will also present new results from the FLAMINGO simulations that demonstrate the rarity of the observed anomaly within a LCDM Universe, while I will also discuss the very promising future lying ahead for cosmic anisotropy studies with galaxy clusters. Finally, to better understand the origin of these apparent anisotropies and bulk flows, we need to map the mass distribution in our cosmic neighborhood accurately. However, a significant fraction of cosmic matter remains undetected (the so-called missing baryons problem). Recently, we reported the first-ever spectroscopic characterization of the density, mass, and temperature of the missing baryons across a pristine 7 Mpc cosmic filament in the Shapley supercluster, finding great agreement with LCDM expectations for the first time. Our study significantly alleviates the long-standing missing-baryon tension in cosmology.
