A gravitational and dynamical model of star formation in Orion
  The Orion Nebula Cluster (ONC) is the most massive region of active star
formation within a kpc of the Sun. Using Gaia EDR3 parallaxes and proper
motions, we examine the bulk motions of stars radially and tangentially
relative to the cluster center. We find an age gradient with distance to the
stars in the ONC, from 385 pc for the oldest stars, to 395 pc for the younger
stars, indicating that the star forming front is propagating into the cloud. We
find an organized signature of rotation of the central cluster, but it is
present only in stars younger than 2 Myr. We also observe a net infall of young
stars into the center of the ONC's deep gravitational potential well. The
infalling sources lie preferentially along the filament, on the other hand,
outflowing sources are distributed spherically around the cluster, and they
have larger velocity dispersion. We further propose a solution to a
long-standing question of why the ONC shows a weak signature of expansion even
though the cluster is likely bound: much of this expansion is likely driven by
unstable N-body interactions among stars, resulting in low-velocity ejections.
Finally we observe a significant infall of stars in various low-mass
star-forming regions towards the Orion Complex at distances as far away as 200
pc, presumably due to a strong gravitational potential of Orion. Through
analyzing signatures imprinted on stellar dynamics across different spatial
scales, these observation shed new light on the signatures of formation and
evolution of young clusters.
