At a meeting of the American Astronomical Society in Kissamee, Florida, on Jan. 6, astrophysicists presented an exciting new idea about where best to focus the search for intelligent extraterrestrial life: dense star clusters.
Globular star clusters are very old, densely populated regions of space that contain as many as a million stars separated by only about 100 light-years. They formed as long as 10 billion years ago and may be particularly good places to search for advanced alien societies, according to Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics (CfA), who presented the findings at a press conference.
“A globular cluster might be the first place in which intelligent life is identified in our galaxy,” says Di Stefano.
Our home galaxy, the Milky Way, contains some 150 globular clusters—but scientists have been skeptical that these densely packed regions of stars are compatible with the existence of planets. This is partly because they have a low metallic content and partly due to the gravitational disturbances likely to affect stars packed so tightly together.
“Globular clusters are very old, and they formed at a time when heavy element content in the universe was smaller than it is today,” said Di Stefano in comments to Gizmodo. “Planets are rich in these heavier elements, and it wasn’t clear if you’d expect to find planets in these low metallicity environments.”
But Di Stefano and her colleague Alak Ray from the Tata Institute of Fundamental Research, in Mumbai, India, argue that globular clusters may be more hospitable to planets than previously suspected.
“It’s premature to say there are no planets in globular clusters,” says Ray in a CfA statement.
First, they note that astronomers have detected the presence of exoplanets—planets outside our solar system—orbiting stars with only a tenth as much metal as the Sun, the statement said. Plus, they say, only gas giants like Jupiter—not small, rocky planets—show a preference for metal-rich stars.
As for gravitational perturbations in the dense ball of stars, the researchers argue that because globular clusters are so ancient, the brightest stars have died out—leaving fainter, but longer lived, red dwarfs.
“Once planets form, they can survive for long periods of time, even longer than the current age of the universe,” says Di Stefano in the statement.
In a cosmic environment where planets have existed for billions of years, the potential for the development of complex, intelligent life exists. And, in a region of space where stars are close together, interstellar travel and communication would be easy.
“We call it the ‘globular cluster opportunity,’” says Di Stefano. “Sending a broadcast between the stars wouldn’t take any longer than a letter from the U.S. to Europe in the 18th century.”
Di Stefano and Ray hope their findings will spark interest from the SETI (Search for Extraterrestrial Intelligence) Institute, so that community can harness the power of its radio and optical telescopes to look for deliberate signals coming from dense globular star clusters.