ALMA Detects First-Ever Hydrogen Recombination Lines From Proplyd Disks in Densely Packed Orion Nebula Cluster

Most stars form in clusters, where hundreds to thousands of stars coevolve in proximal environmental conditions that dictate how planetary systems might develop. Nearby massive stars can also contribute intense ionizing radiation, adding external dynamics that form a shell of ionized gas around a protoplanetary disk and emit unique hydrogen recombination spectral lines. Now, a team of astronomers has used archived Atacama Large Millimeter/submillimeter Array (ALMA) observations to identify for the first time the characteristic radio recombination lines associated with these ionized shells surrounding Solar System-sized proplyd disks in the Orion Nebula Cluster, at a distance of 1000 light-years from Earth.