BlackHoleMergers · Formation of Black Hole Mergers in Dense Stellar Systems

Formation of Black Hole Mergers in Dense Stellar Systems

Gravitational waves (GWs) from the merger of binary black holes (BBHs) have only recently been possible to observe using the pioneering LIGO and Virgo detectors. To date around 50 BBH mergers have been observed and confirmed, which not only have resulted in an enormous amount of new science and open questions, but also marked the beginning of a new era in physics: Gravitational Wave Astrophysics. However, the fundamental question of how these BBHs form in our Universe is still open. In this regard the astrophysical community has proposed several possible formation channels that currently are being tested using -- for the first time -- real GW data. In general, the proposed channels can be divided into the following two categories: i) Isolated BBH formation. In this case BBHs form as a result of isolated stellar evolution. ii) Dynamical BBH formation. In this case two BBHs form as a result of close encounters involving two or more BHs in dense stellar regions. One of the main questions is how to disentangle these two categories using GWs alone, as BHs, as the name indicates, do not emit any light! To use data to probe the astrophysical origin of BBH mergers, one naturally needs accurate models to compare to data. However, as the field of GW astrophysics is still relatively young, we do not have at the moment a complete (theoretical) understanding of how BBHs (might) pair up in the scenarios that are most relevant to test with data at the moment. Therefore, to learn about our Universe using GWs we must first, or at least in parallel to the observations, have a good prediction and understanding of what astrophysical environments we want to look for and probe. That has been my main focus as a Marie Curie Fellow, with a special emphasis on the dynamical formation channel. Astronomy has inspired humans for thousands of years, but our view on the Universe has always been limited to what we can infer from the light emitted from distant stars. With the possibility of detecting GWs we have now opened up a new window into the Universe from which we can see parts we never have been able to see before. So far, we have for the first time seen the formation and interaction of BHs, but as with all other experiments, we also expect to see something new. But what could that be? Time, data and accurate models will soon tell!

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