Scientists are finding it more and more difficult to answer the Fermi paradox: If planets are so common, where is everybody? Where are the advanced civilizations? Researchers from Harvard and the Tata Institute of Fundamental Research, Mumbai, have now suggested that we should look for intelligent life just outside our galaxy.
According to new research presented by Rosanne Di Stefano and Alak Ray at the American Astronomical Society meeting in Kissimmee, Florida today, an interstellar civilization might develop within the globular clusters of stars that surround the Milky Way.
Globular clusters (GCs) are spherical collections of thousands of stars that orbit galaxies in large orbits. Astronomers think there are over 150 GCs surrounding the Milky Way, and Andromeda may have as many as 500.
Stars in globular clusters are usually metal-poor, meaning they lack the elements like carbon, oxygen, and iron that make up most of the composition of rocky planets and living creatures. So far, we have discovered only one exoplanet in a globular cluste,r and some scientists believe that globular clusters don’t have the right conditions to form planets.
Di Stefano and Ray are more optimistic: “It’s premature to say there are no planets in globular clusters,” says Ray in a statement.
In recent years, it has been shown that rocky planets are just as likely to form around metal-poor stars as metal-rich ones. The lack of planetary detections might be due to the fact that globular clusters are several thousand light-years from the Milky Way, making direct observations more difficult.
If planets could evolve, they might be able to survive for a long time, which would make the likelihood of life and then an intelligent species to evolve higher. If such a species existed, they could eventually be capable of navigating throughout the cluster.
Stars within a globular cluster are also significantly closer than stars around the Sun. Proxima Centauri, the closest star to the Solar System, is 4.7 light-years away, while the typical distance between stars in globular clusters is about 20 times smaller than that. Exploration and communication within the cluster would be more manageable than our attempts.
"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.”
She added: “Interstellar travel would take less time too. 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. That means sending an interstellar probe is something a civilization at our technological level could do in a globular cluster.”
Although the idea is intriguing, it’s highly speculative at this stage. The first goal would be to look for planets in clusters, but a positive detection wouldn’t mean life there is probable. Most stars in globular clusters are red dwarfs and they might be less suitable for life than previously thought.