Where and how do black holes form in our Universe? Is the theory put forward by Einstein for describing gravity complete, or does gravity have deeper layers that we have not yet seen and explored? We are now in a golden era to answer these questions sparked by the exceptional first detection of gravitational waves (GWs) in 2015 emitted by the collision of two black holes.
Since this date, we have detected GWs from more than 100 black hole mergers, which have reveled a remarkable diverse landscape of black holes in terms of mass- and spin-distributions throughout the universe, far beyond what we imaged just a few years ago. Generally, what people have inferred from the observed GWs are the BH masses, how they spin, and their orbital motion, but
much more information is likely hidden in the GWs. In My ERC project, I have taken the first steps on how the astrophysical environment impacts the observed GWs, and thereby what we can say about the environment the black holes form and merge in throughout cosmic time using GWs. For example, are the black holes formed in the big bang,
driven through merger in the centers of massive galaxies, assembled through chaotic few-body interactions in dense clusters, or simply a product of binary evolution? My ERC project explores exactly how the underlying formation pathway of the black holes, and how they are brought to merger, will leave imprints in their emitted GW signals, such as frequency modulations
coursed by acceleration of the merging black holes, or modified orbital motion due to interactions with gas, dark matter or other exotic matter components. These modulations will both provide insight into how our Universe is put together throughout cosmic time, as well as help us putting even stronger constraints on Einstein's theory of gravity; topics that
will be exceptional relevant and possible in the coming decades, where we expect to observe hundred-thousands of black hole mergers at distances all the way back near Big Bang.
