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Astronomers led by Simon Portegies Zwart used simulations to reconstruct how three stars were ejected from the star cluster R136, 60,000 years ago. The analysis, in Â鶹ÒùÔºical Review Letters, reveals that five stars were involved in the event in the Tarantula Nebula.

When star clusters form, newly born stars move chaotically through their environment. In this early phase, close encounters can send some stars flying out of the cluster. According to the reconstruction by Portegies Zwart and astronomers from the University of Amsterdam, an encounter involving star VFTS 590, the binary star Mel 39, and another binary, Mel 34, caused the entire system to break apart violently in a single event. This is the first time such a detailed reconstruction has been made of a high-energy encounter like this.

"A reconstruction with this level of precision was long considered impossible," says Portegies Zwart. "But it gives us a unique glimpse into the heart of a star cluster, and the kind of dynamic interactions that take place there. It was expected that such an ejection would involve three, maybe four stars. The fact that we now see evidence of five is a big surprise."

Astronomers have identified around 60 so-called "runaway stars" in R136. These are stars moving away from the cluster at high speed, and they are significantly more massive than previously known runaway stars—some are over 100 times the mass of the sun, and move at speeds of more than 100 km/s.

Earlier research by Stoop and team using data from the Gaia mission had already shown that three of these runaway stars were launched from the core of R136 at around the same time, roughly 60,000 years ago. But the mechanism behind this simultaneous ejection remained unclear.

The new simulations not only confirm the role of these three stars, but also identify two additional ones involved in the event. The calculations point to the binary system Mel 39, whose two stars have masses of 140 and 80 times that of the sun.

The simulations further predict that Mel 39 is moving away from the cluster at 64 km/s, and lies in the same orbital plane as the other ejected binary, Mel 34—one of the heaviest known binary systems in the nearby universe. Thanks to this cosmic detective work, Mel 34 can now also be traced back to the same five-star system, long since disrupted, that once existed in the dense center of R136.