  Recently, several non-interacting black hole-stellar binaries have been
identified in Gaia data. For example, Gaia BH1, where a Sun-like star is in
moderate eccentricity (e=0.45), 185-day orbit around a black hole. This orbit
is difficult to explain through binary evolution. The present-day separation
suggests the progenitor system would have undergone an episode of common
envelope evolution, but a common envelope should shrink the period below the
observed one. Since the majority of massive stars form in higher multiplicity
systems, a triple evolution scenario is more likely for the progenitors of BH
binaries. Here we show that such systems can indeed be more easily explained
via evolution in hierarchical triple systems. von Zeipel--Lidov--Kozai
oscillations or instabilities can delay the onset of the common envelope phase
in the inner binary of the triple, so that the black hole progenitor and
low-mass star are more widely separated when it begins, leading to the
formation of wider binaries. There are also systems with similar periods but
larger eccentricities, where the BH progenitor is a merger product of the inner
binary in the triple. Such mergers lead to a more top-heavy black hole mass
function.
