Gravitational-wave observations provide a new tool to study formation and evolutionary processes of black holes. I present some first attempts to extract astrophysical constraints from the gravitational-wave events of LIGO’s first observing run. In particular, the spin misalignment of the lightest binary black hole detected (GW151226, “the Boxing Day event”) can be used to measure the linear momentum imparted to the black holes at birth, hence the degree of asymmetry of the related supernova explosions. The first events also provide marginal constraints on the presence of multiple merger generations (i.e. merging black holes which are the results of previous mergers, rather than stellar collapse). The future is bright and loud: as hundreds of gravitational-wave events are expected in the next few years, these elusive gravity messengers will soon prove their immense potential to shape our understanding of the astrophysical world.

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