A protostellar system fed by a streamer of 10,500 au length

Abstract

Binary formation is an important aspect of star formation. One possible route for close-in binary formation is disk fragmentation1,2,3. Recent observations show that small-scale asymmetries (<300 au) around young protostars2,4, although not always resolving the circumbinary disk, are linked to disk phenomena5,6. In later stages, resolved circumbinary disk observations7 (<200 au) show similar asymmetries, suggesting that the asymmetries arise from binary–disk interactions8,9,10. We observed one of the youngest systems to study the connection between disk and dense core. We find a bright and clear streamer in chemically fresh material (carbon-chain molecular species) that originates from outside the dense core (>10,500 au). This material connects the outer dense core with the region where asymmetries arise near disk scales. This new structure type, ten times larger than those seen near disk scales, suggests a different interpretation of previous observations: large-scale accretion flows funnel material down to disk scales. These results reveal the under-appreciated importance of the local environment on the formation and evolution of disks in early systems11,12 and a possible initial condition for the formation of annular features in young disks13,14.