Accreting black-holes and neutron stars in X-ray binaries provide an ideal laboratory for exploring the physics of compact objects, yielding not only confirmation of the existence of stellar-mass black holes via dynamical mass measurements, but also the best opportunity for probing high-gravity environments and the physics of accretion; the most efficient form of energy production known. The latter is an essential physical process to understand the universe, playing a crucial role in galactic and extragalactic astronomy. This project aims at exploiting both research opportunities, that is, accretion in the strong gravity regime and dynamical studies of compact objects. To this end, we have put together a strong research team that combines internationally recognised expertise, a successful record of high-impact results, and access to the best available observing facilities to carry out state-of-the-art research in X-ray binaries.

Firstly, X-ray binaries offer the opportunity to study accretion at its best, since their relevant changes occur on convenient time scales for human beings. This project focuses on the universal relation between black-hole accretion and ejection processes in the form of collimated jets and wide-angle winds. We want to establish which are the main observational properties of the optical and near-infrared winds that we
have discovered, and which is its impact, launching mechanism and physical connection with radio jets and hot X-ray winds. Our second goal is to significantly expand the mass distribution of compact objects in X-ray binaries, which can be confronted with that derived from gravitational wave events in order to constrain the physical models behind the collapse of massive stars, as well as setting constraints on the equation of state of nuclear matter.