Almost all massive stars have bound stellar companions , existing in binaries or higher-order multiples [ 1 , 2 , 3 , 4 , 5 ] .
While binarity is theorized to be an essential feature of how massive stars form [ 47 ] , essentially all information about such properties is derived from observations of already formed stars , whose orbital properties may have evolved since birth .
Little is known about binarity during formation stages .
Here we report high angular resolution observations of 1.3 mm continuum and H30 \alpha recombination line emission , which reveal a massive protobinary with apparent separation of 180 au at the center of the massive star-forming region IRAS07299-1651 .
From the line-of-sight velocity difference of 9.5 \ > \mbox { km s } ^ { -1 } of the two protostars , the binary is estimated to have a minimum total mass of 18 solar masses , consistent with several other metrics , and maximum period of 570 years , assuming a circular orbit .
The H30 \alpha line from the primary protostar shows kinematics consistent with rotation along a ring of radius of 12 au .
The observations indicate that disk fragmentation at several hundred au may have formed the binary , and much smaller disks are feeding the individual protostars .