A close encounter of the massive kind

TL;DR

This study combines multiple observational techniques to analyze the orbit of the massive multiple star system HD 93 129 Aa,Ab, predicting significant wind interactions and potential three-body dynamics during its upcoming periastron passage.

Contribution

It provides the first detailed orbital analysis of HD 93 129 Aa,Ab using diverse observational data and suggests possible complex interactions including binary and three-body phenomena.

Findings

System has a highly eccentric orbit with e>0.92.

Evidence suggests HD 93 129 Aa may be a binary itself.

Periastron passage will likely produce unprecedented wind collision phenomena.

Abstract

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.