Martedì 2 marzo alle ore 15:00, Beta Lusso del Dipartimento di Fisica e Astronomia dell’Università degli Studi di Firenze, terrà il Colloquio di Fisica dal titolo "Quasars as standard(izable) candles (and the physics behind)".
I will present the latest results on our analysis of the non-linear X-ray to ultraviolet luminosity relation in a sample of optically selected quasars from SDSS, cross-matched with the most recent XMM-Newton and Chandra catalogues. I will show that this correlation is very tight, implying that the observed relation is the manifestation of an ubiquitous (but still unknown) physical mechanism, that regulates the energy transfer from the accretion disc to the X-ray emitting corona in quasars. I will also discuss what the perspectives of quasars in the context of observational cosmology are and present new measurements of the expansion rate of the Universe in the redshift range z=0.5-7.5 based on a Hubble diagram of quasars.
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