Casting Light on the Dark Universe, Euclid's Mission Shows Promise

On December 7, 1968, the National Aeronautics and Space Administration (NASA) successfully launched the first functional space telescope into orbit. In the 55 years since, dozens of these crafts have embarked on missions of discovery, advancing and transforming our understanding of the cosmos.

Among the latest is Euclid, a wide-angle space telescope developed by the European Space Agency (ESA). Equipped to chart portions of the universe that are not directly observable and currently shrouded in mystery, Euclid is working to generate a three-dimensional map unlike any other, surveying billions of galaxies out to 10 billion light-years. This past month, the first images from its journey were released.

Joey Neilsen, PhD, is a world-renowned astrophysicist, a frequent collaborator with NASA and an assistant professor in Villanova University’s College of Liberal Arts and Sciences. From his perspective, Euclid’s early returns evidence its voyage’s incredible potential.

“In Euclid’s first image of the Perseus cluster, the sheer number of galaxies is really astonishing,” said Dr. Neilsen. “We talk a lot about how the universe is mostly empty space—and it is!—but it’s also enormous, and it’s really stunning that there’s room for so many galaxies in just a small patch of sky. There are 1,000 galaxies here huddled together in this cluster and over 100,000 in the background.

“I also note some pale purple patches in the image of NGC 6822. These are planetary nebulae, the layers of gas and dust blasted off by stars at the ends of their lives. It’s amazing to be able to see these so clearly in images that show the entire galaxy and its environment at the same time.”

According to Dr. Neilsen, Euclid’s remarkable visuals are the product of a calculated tradeoff. The ESA craft sacrifices the fine resolution of images taken by other observatories, like NASA’s James Webb Space Telescope, to capture cosmic phenomena in greater breadth. By collecting these visuals, Euclid aims to spark breakthroughs on subjects as of yet understudied—breakthroughs that could benefit Dr. Neilsen’s field of research.

“Euclid’s mission is to understand the evolution of the dark components of the universe: the invisible dark matter whose gravity holds large structures like galaxies and galaxy clusters together and the dark energy responsible for the accelerating expansion of the universe,” he explained. “Much of my research focuses on a different aspect of the dark universe (black holes), but there is a puzzle that might connect: observations of very distant galaxies show there were very massive black holes very early on. How did these behemoths grow so big so fast? If would be neat if Euclid helped us to better understand the early universe in a way that informed our understanding of the growth of black holes.”

In tracking and investigating the dark entities that compose and mold the cosmos, Euclid could very well offer insights into the history and development of over 95% of all energy and matter—and perhaps into the very fabric of existence itself. It is reasonable to wonder whether, when its mission is complete in six years’ time, the telescope could provide us with answers to questions that have gone unaddressed for six billion years.

“For me, the best-case scenario would be that Euclid would show clear evidence of something that’s hard to explain with our current models,” said Dr. Neilsen.

“For example, right now, we have ‘Hubble tension,’ a discrepancy between measurements of the expansion of the universe from when it was young and from the current era… The moments when things don’t add up are the ones where we learn the most about how the universe works. So, I’ll keep my fingers crossed for a surprise and for more to learn over the next six billion years.”