Accretion is vital for understanding the properties of a number of astrophysical objects, including massive young stars and black holes. For the former, accretion drives the stellar mass growth and multiplicity through gas fragmentation. It also powers strong outflows that regulate the interstellar medium.
For black holes, only accretion allows for electromagnetic detection. Hence, the multi-messenger astronomy, for which the loudest sources of gravitational waves, binary black holes, are playing a central role, eventually depends on the physics of accretion around such systems.
In this talk, I will highlight some of my work in these two fields: massive star formation and accreting binary black holes, via numerical simulations and comparisons to observations, and I will show how such a priori different systems can be studied with similar techniques.