Flipping-up the field: gravitational feedback as a mechanism for young
  clusters dispersal
  Recent analyses of Gaia data have provided direct evidence that most young
stellar clusters are in a state of expansion, with velocities of the order of
~0.5 km/s. Traditionally, expanding young clusters have been pictured as
entities that became unbound due to the lack of gravitational binding once the
gas from the parental cloud that formed the cluster has been expelled by the
stellar radiation of the massive stars in the cluster. In the present
contribution, we used radiation-magnetohydrodynamic numerical simulations of
molecular cloud formation and evolution to understand how stellar clusters form
and disperse. We found that the ionising feedback from the newborn massive
stars expels the gas from the collapse centre, flipping-up the gravitational
potential as a consequence of the mass removal from the inside-out. Since
neither the parental clouds nor the formed shells are distributed symmetrically
around the HII region, net forces pulling out the stars are present,
accelerating them towards the edges of the cavity. We call this mechanism
``gravitational feedback", in which the gravity from the expelled gas appears
to be the crucial mechanism producing unbound clusters that expand away from
their formation centre in an accelerated way in young stellar clusters. This
mechanism naturally explains the "Hubble flow-like" expansion observed in
several young clusters.
