We have used ( a ) HST ACS imaging and STIS spectroscopy , ( b ) ground-based PIONIER/VLT long-baseline interferometry , and ( c ) ground-based spectroscopy from different instruments to study the orbit of the extreme multiple system HD 93 129 Aa , Ab , which is composed of ( at least ) two very massive stars in a long-period orbit with e > 0.92 that will pass through periastron in 2017/2018 .
In several ways , the system is an \eta Car precursor .
Around the time of periastron passage the two very strong winds will collide and generate an outburst of non-thermal hard X-ray emission without precedent in an O+O binary since astronomers have been able to observe above Earth ’ s atmosphere .
A coordinated multiwavelength monitoring in the next two years will enable a breakthrough understanding of the wind interactions in such extreme close encounters .
Furthermore , we have found evidence that HD 93 129 Aa may be a binary system itself .
In that case , we could witness a three-body interaction that may yield a runaway star or a stellar collision close to or shortly after the periastron passage .
Either of those outcomes would be unprecedented , as they are predicted to be low-frequency events in the Milky Way .