Old, dense and isolated clusters of stars might be the perfect place to find intelligent life beyond Earth, say scientists who presented a study about how so-called "globular clusters" may be a cradle of life for advanced civilizations.
"If they house planets, globular clusters provide ideal environments for advanced civilizations that can survive over long times," astronomer Rosanne Di Stefano, with the Harvard-Smithsonian Center for Astrophysics, said in a summary of a paper to be presented at the American Astronomical Society meeting in Kissimmee, Fla., this week.
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"If planets are found and if our arguments are correct, searches for intelligent life are most likely to succeed when directed toward globular clusters," Di Stefano wrote.
Globular clusters typically contain about 1 million stars in a region just 100 light years across. The Milky Way galaxy has about 150 globular clusters, most located in the galaxy's outer regions. The clusters are about 12 billion years old.
So far, only one planet has been found in a globular cluster, but Di Stefano discounts critics who say clusters' old, metal-poor stars are poor hosts for planets.
Exoplanets have been found stars with only one-tenth of the heavy elements that are found in the sun, Di Stefano said.
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"It's premature to say there are no planets in globular clusters," Alak Ray, with the Tata Institute of Fundamental Research in Mumbai, said in a press release.
If habitable planets can form in globular clusters and survive for billions of years, life would have ample time to become increasingly complex, and even potentially develop intelligence, the scientists said.
"It would be very serene to live in a globular cluster, but it would also be bright because there would be so many nearby stars," Di Stefano told reporters during a press conference on Wednesday.
Global cluster civilizations also may be able to communicate with one another far easier than what Earthlings can manage, as the nearest star to our solar system is four light years away, roughly 24 trillion miles.
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In globular clusters, neighbor stars are relatively close, just 1 trillion miles apart.
"The very old, stable populations, coupled with the very small distances between stars might make it possible for civilizations in globular clusters to travel and possibly to develop outposts in relatively short times," Di Stefano.
An independent outpost adds a margin of safety that a catastrophic event, such as a comet or asteroid impact, won't wipe out the species, she added.
"Globular clusters may contain very old, advanced civilizations," Di Stefano said.