The universe is filled with galaxies that clump together like cosmic metropolises in the vast emptiness of space. Now astronomers have taken a bunch of baby pictures of these galaxy clusters, capturing them when they’re just a couple billion years old (that’s young, considering the universe is 13.8 billion years old). With more than 200 likely baby clusters, it’s the biggest such haul ever, providing clues to dark matter and how galaxies form and evolve over time.
Galaxy clusters form the structural backbone of the universe—it’s where all the stuff is. Astronomers have seen plenty of these clusters throughout the universe, but what’s been elusive are the young clusters. The farther you look in space, the longer it takes the light to reach your eyes, and the farther back in time you’re looking. So the youngest clusters have to be really distant, which makes them really dim. And because they’re young, they haven’t had much time to build a lot of bright stars, making them even harder to detect.
Clusters are also difficult to find because they occupy just a sliver of the enormous expanse of space. “These are what I would call the one-percent regions—these are the most concentrated regions in our entire universe,” says David Koo, an astronomer at the University of California, Santa Cruz. “They’re like the ultra wealthy parts of space.”