Molecular contrails -- triggered contraction by passages of massive
  objects through molecular clouds
  We study the effects of passages of compact objects such as stars, star
clusters, and black holes through molecular clouds, and propose that the
gravitational interaction between the compact object and the ambient gas can
lead to the formation of thin and collimated features made of dense gas, which
we call "molecular contrails". Supercritical contrails can collapse further
leading to triggered star formation. The width of a molecular contrail is
determined by the mass and velocity of the compact object and the velocity
dispersion of the ambient molecular medium. Under typical conditions in the
Milky Way, passages of stellar-mass objects lead to the formation of width
$d\gtrsim 0.01\;\rm {parsec}$ contrails, and passages of star clusters lead to
the formation of $d\gtrsim 1\;\rm {parsec}$ contrails. We present a few
molecular contrail candidates from both categories identified from ALMA 1.3mm
continuum observations of star-forming regions and the $^{13}$CO(1-0) map from
the Galactic Ring Survey respectively. The contrails represent an overlooked
channel where stars and gas in the Galactic disk interact to for structures.
They also present a potential way of detecting dark compact objects in the
Milky Way.
