Here we confirm Melnick 34 , an X-ray bright star in the 30 Doradus region of the Large Magellanic Cloud , as an SB2 binary comprising WN5h+WN5h components .
We present orbital solutions using 26 epochs of VLT/UVES spectra and 22 epochs of archival Gemini/GMOS spectra .
Radial-velocity monitoring and automated template fitting methods both reveal a similar high eccentricity system with a mass ratio close to unity , and an orbital period in agreement with the 155.1 \pm 1 day X-ray light curve period previously derived by Pollock et al .
Our favoured solution derived an eccentricity of 0.68 \pm 0.02 and mass ratio of 0.92 \pm 0.07 , giving minimum masses of M _ { \text { A } } sin ^ { 3 } ( i ) = 65 \pm 7 M _ { \odot } and M _ { \text { B } } sin ^ { 3 } ( i ) = 60 \pm 7 M _ { \odot } .
Spectral modelling using WN5h templates with cmfgen reveals temperatures of T \sim 53 kK for each component and luminosities of log ( L _ { \text { A } } /L _ { \odot } ) = 6.43 \pm 0.08 and log ( L _ { \text { B } } /L _ { \odot } ) = 6.37 \pm 0.08 , from which BONNSAI evolutionary modelling gives masses of M _ { \text { A } } = 139 ^ { +21 } _ { -18 } M _ { \odot } and M _ { \text { B } } = 127 ^ { +17 } _ { -17 } M _ { \odot } and ages of \sim 0.6 Myrs .
Spectroscopic and dynamic masses would agree if Mk34 has an inclination of i \sim 50 \degree , making Mk34 the most massive binary known and an excellent candidate for investigating the properties of colliding wind binaries .
Within 2-3 Myrs , both components of Mk34 are expected to evolve to stellar mass black holes which , assuming the binary system survives , would make Mk34 a potential binary black hole merger progenitor and gravitational wave source .