Most of the universe's massive stars do not live alone. Astronomers estimate that at least ninety per cent of them exist in binary or multiple systems, yet how such pairs actually come together has remained stubbornly unclear, because massive stars form quickly, far away and deep inside veils of dust. A new study in Nature Astronomy, with the participation of Guido Garay of the Universidad de Chile's Faculty of Physical and Mathematical Sciences, now offers an unusually detailed answer.
The paper, titled An eccentric massive protobinary assembled via a core-merger parabolic encounter, reconstructs the architecture of a forming massive binary in three dimensions. The data show the two protostars locked in highly eccentric, almost parabolic orbits, while their accretion discs sit strongly misaligned with respect to the orbital plane. That geometry is the signature of a violent origin: two dense cores merging through a close parabolic encounter rather than a single cloud serenely splitting in two.
The observations, which drew on instruments including the James Webb Space Telescope, matter well beyond one system. Massive stars end their lives as supernovae and leave behind the neutron stars and black holes whose mergers are now routinely detected through gravitational waves. Understanding how such pairs are bound together at birth therefore feeds directly into the astrophysics of compact-object populations, and gives theorists a concrete, observed formation pathway to model.