We know that the Milky Way galaxy is made up of hundreds of billions of stars hosting as many or more planets, and that the Milky Way itself is only one of as many as 200 billion galaxies that make up the observable universe. But that may be only half the story. A recent study of electromagnetic background light has uncovered something that may change our understanding of the universe forever: that there may be as many stars floating freely outside of galaxies as there are within them. And if that’s the case, it’s entirely possible that we’ve been looking for extraterrestrial life in all the wrong places.
Astronomers only first discovered rogue intergalactic stars in 1997 (h/t Hubble Space Telescope). But conventional wisdom has long suggested that there aren’t very many of these relative to the number of stars one might find in a single galaxy, so they’ve never factored heavily into exobiology. Now that we know there are more of them—many more of them—than we’d anticipated, they raise some really difficult, and interesting, questions about which parts of our universe are habitable.
And like most exobiology-related questions, it’s a crapshoot. We could argue that rogue intergalactic stars have a lower rate of planetary formation, and subsequently a lower rate of habitable planet formation, than galactic stars; we could also argue that the planets they do create make for safer habitats, as they’re off on their own and safely isolated from galactic hazards. The one thing we can reasonably guess about intergalactic stars is that if their planets do host intelligent beings, there aren’t many astrologers among them; our starry sky is evidence of our solar system’s place in the glowing heart of the Milky Way. In most of the observable universe, midnight is a much darker hour—and sunrise, with the potential for life that it implies, the greatest luxury of all.