Bence Kocsis (Oxford) "On the AGN Origin of Gravitational Wave Sources observed by LIGO/VIRGO"
With the detection of gravitational waves emitted during black hole and neutron star mergers, LIGO has recently opened the field of gravitational wave astrophysics. In this talk I will review the astrophysical processes that may be responsible for the formation of the observed events. The event rate distribution with mass, spins, eccentricity and redshift may be used to discriminate among different processes that lead to black hole mergers. I will show that the standard astrophysical merger channels are already in tension with LIGO/VIRGO observations. New ideas may be needed to explain the origin of the detected sources. I will discuss the possibility that black hole mergers happen in active galactic nuclei where the interaction with a gaseous disk helps to form binaries, and a combination of dynamical and gas effects facilitate the merger of the binaries.
Carme Gallart (IAC) "The History of the Galactic disc and halo from Gaia DR2 HR diagram fitting"
Abstract: Gaia has provided distances and photometry, and thus colour-magnitude diagrams in the absolute plane, for stars over an unprecedented vast volume in the Milky Way, encompassing significant fractions of the thin and thick disk, and halo. This has allowed us, for the first time, to derive unprecedentedly detailed star formation histories from direct modelling of these colour-magnitude diagrams, using the same techniques that have been proven successful for external galaxies in the Local Group. I will discuss our first results for a volume of 2 Kpc radius from the Sun. They have allowed us to date the first events involved in the formation of the inner Milky Way halo (Gallart et al. 2019, NatAstro) and to determine the presence of epochs of enhanced star formation well constrained in time, that can be associated to the various pericentric passages of the Sagittarius dwarf galaxy (Ruiz-Lara et al. 2020, NatAstro). Additionally, we have obtained results of unprecedented clarity regarding the vertical distribution of ages en the Milky Way disk (Gallart et al. 2020, in prep).