Clusters of stars on the outskirts of the galaxy may harbor extraterrestrial life, argue scientists at the American Astronomical Society’s annual meeting in Kissimmee, Florida. The astronomers believe regions of densely packed stars, known as globular clusters, could be home to intelligent civilizations.
The Milky Way is packed with approximately 150 globular clusters, a spherical collection of tightly bound stars that orbit a galactic core. They contain approximately 100 million stars and typically span 100 light years across.(1,2)
“A globular cluster might be the first place in which intelligent life is identified in our galaxy,” said lead author Rosanne DiStefano of the Harvard-Smithsonian Center for Astrophysics (CfA). She presented her research at a meeting with the American Astronomical Society earlier this week.(1)
Lots of stars, few planets
Globular clusters are extremely old objects with roots tethered to the inception of the Milky Way about 10 billion years ago. Consequently, globular clusters tend to harbor fewer planets, since they are home to first generation stars, which lack heavier elements like iron and carbon that are necessary to create rocky planets. Thus far, only one planet has been found inside a globular cluster.
Nevertheless, DiStefano and her team believe the lack of planets found in globular clusters should not be cause for concern. Exoplanets have been discovered around stars that have one-tenth the iron of our own sun. And although Jupiter-like planets tend to be found around chemically rich stars, Earth-like planets have been found around stars of all shapes and sizes.
“It’s premature to say there are no planets in globular clusters,” states Alak Ray, a researcher involved in the study.(1)
Interstellar travel easier for civilizations in globular clusters
The reason DiStefano and her team believe globular clusters may be a hot spot for intelligent life is that the stars are relatively close to each other, making it easier for an intelligent civilization to hop from one solar system to the next. Furthermore, globular clusters are as old as the galaxy, meaning there has been more than enough time for life to evolve.
Regardless, the close proximity of planets doesn’t necessarily increase the likelihood of life. The crowded nature of globular clusters could pose a threat to exoplanets that do form. The gravitational pull of a star could intersect with a nearby solar system, thereby flinging would-be habitable worlds into frigid interstellar space.
However, a star’s habitable zone, a region around a star that can support liquid water, varies from star to star. Brighter stars tend to have distant habitable zones, whereas dimmer stars tend to have closer habitable zones.
Red dwarfs a hot spot for life
The bulk of stars in globular clusters are red dwarfs, which are small and relatively cool. Any exoplanet that might form in a globular cluster would be closely latched to their star, keeping the exoplanets safe from the threat of interstellar interaction.
“Once planets form, they can survive for long periods of time, even longer than the current age of the universe,” notes DiStefano.(1)
The researchers press that an intelligent civilization would enjoy a different environment from our own. The nearest star from our solar system is roughly 24 trillion miles away. By contrast, the closest star relative to another in a globular cluster is twenty times closer, or just one trillion miles away. This would make interstellar communication and exploration much easier, claim the researchers.
“The Voyager probes are 100 billion miles from Earth, or one-tenth as far as it would take to reach the closest star if we lived in a globular cluster,” said DiStefano.(1)
“That means sending an interstellar probe is something a civilization at our technological level could do in a globular cluster,” she added.(1)