The study, led by astronomer Hugues Sana and student Toayo van Boeckel of the University of Amsterdam, suggests the binary star system potentially weighed 300 to 400 solar masses at birth.
"It is a mystery how extremely massive stars form," Amsterdam co-researcher Frank Tramper said. "According to the most widely accepted theories, stars of hundreds of solar masses can only form in massive star clusters.
However, the binary star R144 lies in an outer area of a star-forming region in the Large Magellanic Cloud known as 30 Doradus, the astronomers said.
"The fact that R144 lies far out from the central star cluster in 30 Doradus is possibly an indication that these systems can form in isolation," Tramper said.
The spectral lines of R144 suggest the binary system is formed by two hydrogen-rich stars with similar masses, the researchers said.
R144 may have been formed in the central star cluster then later ejected by dynamical interactions with other massive stars, they said.
Further observations are needed to determine whether R144 is indeed a "runaway" binary star, the researchers said, and to definitively establish its mass to decide whether R144 really is the most massive double star discovered so far.