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 >= 0.01 pc contrails, and passages of star clusters lead to the formation of d >= 1 pc contrails. We present a few molecular contrail candidates from both categories identified from ALMA 1.3 mm continuum observations of star-forming regions and the (CO)-C-13(1-0) map from the Galactic Ring Survey, respectively. The contrails represent an overlooked channel where stars and gas in the Galactic disc interact to form structures. They also present a potential way of detecting dark compact objects in the Milky Way.