The stars, which were estimated to be between 40 and 100 times more massive than the sun, didn't last long. About 5 million years after forming, they became black holes that orbited one another for another 10.3 billion years.
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The pair then merged in crash so violent that it warped the interwoven fabric of space and time, setting off a wave, which 1.2 billion years later was detected by Laser Interferometer Gravitational-Wave Observatory, or LIGO, on Earth.
"The black holes were monsters, and the results show that their progenitor stars would have been some of the brightest and most massive in the universe," physicist J.J. Eldridge, with the University of Auckland in New Zealand, writes in a commentary in this week's Nature.
"If the proposed age of the stars' formation is correct, then they might have contributed to the re-ionization of the universe - one of the key events in the universe's evolution," Eldridge added.
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The research is based on very precise numerical simulations of the formation of binary black holes from isolated pairs of binary stars, Belczynski and colleagues write.
The models serve as "a framework within which to interpret the first gravitational-wave source ... and to predict the properties of subsequent binary-black-hole gravitational-wave events," the scientists said.
In addition to estimating the number of black hole mergers, the study has implications for understanding how stars evolve and die.
"Belczynski and colleagues' study is tremendously exciting," Eldridge said. "With each gravitational-wave signal detected we'll learn something new."