On the physical mechanisms governing the cloud lifecycle in the Central
  Molecular Zone of the Milky Way
  We apply an analytic theory for environmentally-dependent molecular cloud
lifetimes to the Central Molecular Zone of the Milky Way. Within this theory,
the cloud lifetime in the Galactic centre is obtained by combining the
time-scales for gravitational instability, galactic shear, epicyclic
perturbations and cloud-cloud collisions. We find that at galactocentric radii
$\sim 45$-$120$ pc, corresponding to the location of the '100-pc stream', cloud
evolution is primarily dominated by gravitational collapse, with median cloud
lifetimes between 1.4 and 3.9 Myr. At all other galactocentric radii, galactic
shear dominates the cloud lifecycle, and we predict that molecular clouds are
dispersed on time-scales between 3 and 9 Myr, without a significant degree of
star formation. Along the outer edge of the 100-pc stream, between radii of 100
and 120 pc, the time-scales for epicyclic perturbations and gravitational
free-fall are similar. This similarity of time-scales lends support to the
hypothesis that, depending on the orbital geometry and timing of the orbital
phase, cloud collapse and star formation in the 100-pc stream may be triggered
by a tidal compression at pericentre. Based on the derived time-scales, this
should happen in approximately 20 per cent of all accretion events onto the
100-pc stream.
