This past February, four distinguished astrophysicists —Jonathan Carroll-Nellenback, Adam Frank, Jason Wright, Caleb Scharf— suggested in new research that Earth may have remained unvisited by space-faring civilizations all the while existing in a galaxy of interstellar civilizations seeded by moving stars that spread alien life, offering a solution to the perplexing Fermi paradox. They concluded that a planet-hopping civilization could populate the Milky Way in as little as 650,000 years.
Journey Through the Galaxy
The team’s research suggests a space-faring civilization could planet-hop across the galaxy, because the orbits of stars through the Milky Way can help distribute life. “The sun has been around the center of the Milky Way 50 times,” said Jonathan Carroll-Nellenback, at the University of Rochester, who led the study.
“Stellar motions,” he adds, “alone would get you the spread of life on time scales much shorter than the age of the galaxy.” But, according to their simulations, natural variability will mean that sometimes galaxies will be settled, but often not, as well as some planets being visited, and some not, perhaps, such as Earth— solving Fermi’s annoying paradox.
Globular Cluster Abodes
In 2016, astrophysicist Rosanne DiStefano of the Harvard-Smithsonian Center for Astrophysics (CfA) proposed in her study, Globular Clusters Could Nurture Interstellar Civilizations, that one of the 150 ancient, densely packed, globular star clusters that exist on the outskirts of the the Milky Way since its birth and that average about 100 light-years across, could be extraordinarily good places to look for space-faring civilizations. and might be the first place in which intelligent life is identified in our galaxy. The predominant stars in globular clusters are faint, long-lived red dwarfs. Any potentially habitable planets they host would orbit nearby and be relatively safe from stellar interactions.
“Once planets form, they can survive for long periods of time, even longer than the current age of the universe,” explains DiStefano. The stunning image above from the NASA/ESA Hubble Space Telescope shows globular cluster relic NGC 1866.
Such a civilization would enjoy a very different environment than our own, reports the Harvard-Smithsonian Center for Astrophysics. “The nearest star to our solar system is four light-years, or 24 trillion miles, away. In contrast, the nearest star within a globular cluster could be about 20 times closer – just one trillion miles away. This would make interstellar communication and exploration significantly easier.”
“Globular Cluster Opportunity”
“We call it the ‘globular cluster opportunity,'” says DiStefano. “Sending a broadcast between the stars wouldn’t take any longer than a letter from the U.S. to Europe in the 18th century.”
“Interstellar travel would take less time too,” she adds. “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.”
Carroll-Nellenback and his coauthors included impediments to settlement such as climate change apocalypse in their model and ran simulations with different star densities, seed civilizations, spacecraft velocities and other variations. They suggested that it’s possible that the Milky Way is partially or intermittently settled and that perhaps interstellar explorers visited our solar system and Earth in the distant past..
We’ll never know.
But as Harvard’s Avi Loeb conjectures, aliens are not science fiction: “I don’t see extraterrestrials as more speculative than dark matter or extra dimensions. I think it’s the other way around.” Loeb is the author of the upcoming Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, a mind-bending journey through the furthest reaches of science, space-time, and the human imagination, published on January 26, 2021
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