Gas dynamics in massive dense cores in Cygnus-X

Context. The physical conditions in massive dense cores (MDCs) that form massive stars and clusters, are not well constrained. Few observations have been made to confront the theories. An extensive study has started of the most massive and youngest cores in the Cygnus-X molecular complex, whose first results have uncovered exceptional fragmentation properties in a sample of five cores where individual massive protostars have been recognized.