Finding binary black holes in the Milky Way with LISA

We determine the main properties of the Galactic binary black hole (BBH) population detectable by Laser Interferometer Space Antenna (LISA) and strategies to distinguish them from the much more numerous white dwarf binaries. We simulate BBH populations based on cosmological simulations of Milky Way-like galaxies and binary evolution models. We then determine their gravitational wave emission as observed by LISA and build mock catalogues. According to our model, LISA will detect ≈4 (6) BBHs assuming 4 (10) yr of operations. Those figures grow to ≈6 (9) when models are re-normalized to the inferred LIGO/Virgo merger rates. Largely independent on mass and distance, sources emitting at f > 0.5 mHz - 40 per cent (70 per cent) of the detections - have a measurable frequency drift, which allows a good enough chirp mass measurement to separate them from the much lighter white dwarf and neutron star binaries. Most of the remaining, lower frequency, sources should be identifiable by their lack of electromagnetic (EM) counterpart within ≈100 pc. These results are robust with respect to the current uncertainties of the BBH merger rate as measured by LIGO/Virgo as well as the global mass spectrum of the binaries. Based on the LIGO/Virgo merger rate, we determine that there is a 94 per cent chance that LISA finds at least one of these systems within 4 yr, which will allow us to pinpoint the conditions where they were formed and possibly find unique EM signatures.