Most stars form in molecular clusters, with specific environmental conditions dictating how planetary systems develop. Nearby massive stars can also influence by intense ionizing radiation, which can create a shell of ionized gas around a protoplanetary disk and emit unique hydrogen recombination spectral lines.
Recently a scientific team led by Ryan Boyden/University of Virginia has used archive Atacama Large Millimeter/submillimeter Array (ALMA) data to identify for the first time the characteristic radio recombination lines associated with these ionized shells surrounding Solar System-sized protoplanetary disks in the Orion Nebula Cluster, at 1000 light-years from us. The results of the study are published in the following scientific paper: Boyden et al. Discovery of Radio Recombination Line Emission from Proplyds in the Orion Nebula Cluster. Read more.
Image: © Boyden et al. (2025); The Orion Nebula Cluster, as seen with Hubble Space Telescope/Advanced Camera for Surveys (Ricci et al. 2008). The white dashed line depicts the field of view of the 3.1 mm ALMA mosaic. Blue circles indicate proplyds detected in H41α. The red circle marks the proplyd that is also detected in He41α. Gray circles indicate the positions of 3.1 mm continuum detections that are not detected in H41α or He41α. The cyan star indicates the position of the ionizing source θ1 Ori C.