Discovery of a septuple protostellar system--implications for the origin of extreme high-order multiplicity

Stellar multiple systems play a pivotal role in cluster dynamics and stellar evolution, leading to intense phenomena like X-ray binaries, gamma-ray bursts, Type Ia supernova, and stellar mergers. However, their origin remains poorly understood, and there are no direct observations of multiple systems with more than five members during the early stages of star formation. We report the discovery of a septuple protostellar system embedded in a Keplerian disk within the high-mass star-forming region NGC6334IN. The stability analysis reveals that the disk is dynamically unstable, aligning with the observed separations of the septuple system originating from disk fragmentation. These findings suggest that the septuple system formed via fragmentation of a gravitationally unstable disk, shedding new light on the formation of extreme high-order multiplicity in cluster environments.