A network of second-generation laser interferometric gravitational-wave (GW) observatories is presently under construction. The US-based Advanced Laser Interferometer Gravitational Wave Observatory (aLIGO)[1] is expected to have its initial observing run in 2015 utilizing observatories in Hanford, Washington and Livingston, Louisiana (denoted ‘H’and ‘L’, respectively). aLIGO will then work towards reaching design sensitivity, expected in 2018–20 [2]. The French–Italian Advanced Virgo (AdV) observatory [3, 4](denoted ‘V’) is expected to follow shortly after the aLIGO instruments. The cryogenically cooled KAGRA observatory [5, 6] and a India-based aLIGO facility [7, 8] are due to begin operations around 2020, providing a 5-site network to explore the GW sky in detail. These second-generation observatories will have an order of magnitude increase in sensitivity over their first-generation counterparts and will be sensitive to a broader range of GW frequencies [1, 4, 6]. One of the primary observational targets for this global network is the inspiral, merger and ringdown of a binary system containing two black holes (BHs)[9]. With aLIGO and AdV operating at their final design sensitivities it is expected that 0.4–1000 binary BH (BBH) coalescences will be observed per year of operation [10]. Directly observing the collision of two BHs will allow GW astronomers to understand the physics of BH spacetimes and to explore the strong-field conditions of the theory of general relativity [11].

Exploring the underlying mass and spin distributions of stellar-mass BHs can tell us a great deal about the end stages of massive-star evolution. The mass measurements of compact objects made to date suggest a gap between the most massive neutron stars (≲ 3M⊙)[12] and the least massive BHs (≳ 5 M⊙)[13]. It is still an open question as to whether this gap is real and the result of formation mechanisms, or simply due to observational biases [14].