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

Dec 23, 2023

3 min

Joey Neilsen, PhD

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.”


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Joey Neilsen, PhD

Joey Neilsen, PhD

Associate Professor of Physics

Professor Neilsen, PhD, uses X-ray telescopes to study black hole accretion disks, winds, and relativistic jets.

Black HolesBlack Hole AccretionSupermassive Black HolesAccretion DisksAccretion Disk Winds
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With Sunshine Protection Act Under Consideration, Villanova Sleep Expert Speaks to the Pros and Cons of Changing the Clocks featured image

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With Sunshine Protection Act Under Consideration, Villanova Sleep Expert Speaks to the Pros and Cons of Changing the Clocks

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Solar Déjà Vu: Eclipses, Like the One in August, Follow Predictable Cycles, Explains Villanova Astronomer featured image

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Solar Déjà Vu: Eclipses, Like the One in August, Follow Predictable Cycles, Explains Villanova Astronomer

As the moon passes in front of the sun on August 12, 2026, viewers along the eclipse’s path of totality in Iceland, Greenland and Northern Spain will be treated to more than two minutes of daytime darkness. For many, it will be their first experience in totality. For the eclipse itself, it’s just another slightly different chapter in a millennium-long rinse and repeat. That’s because every eclipse belongs to what is called a saros series—a “family” of eclipses that follow a predictable schedule. A saros series begins and ends with partial eclipses near opposite poles of the Earth, and in between may feature annular, hybrid or total eclipses—like the kind occurring this August—across the world. “Then the series will end,” said Frank Maloney, PhD, associate professor of Astrophysics and Planetary Science at Villanova University. “New saros series are always coming into being, and old ones fading from existence. While they are here, they usually have between 70-73 eclipses over a span of 1,200-1,300 years.” Within the series is what is known as a saros cycle. It’s a period of roughly 18 years, 11 days and eight hours, when a natural synchronization of the moon’s three lunar phases arises. That synchronization can predict both lunar and solar eclipses, which follow very similar geometrics to the ones that precede and follow in their series. But why, then, aren’t all eclipses in a series over the same viewing area? The answer lies more with the movement of the Earth than with the eclipse. Within each series, the biggest cause of change from eclipse to eclipse comes from that last eight hours. It’s only the length of a workday, but each cycle, the Earth has rotated an additional 120 degrees from the previous. While the eclipse itself remains very similar to its predecessor and successor in the series, the viewing area does not. “Every fourth eclipse, or roughly every 54 years, you are back to where you began,” said Dr. Maloney. “That fourth eclipse in a saros is referred to as an exeligmos. But even that eclipse won’t follow the exact same path for a few reasons, including slight variations in the moon’s orbital node and distance from Earth.” Same region, but different track. The August 2026 eclipse will pass over Greenland, Iceland and Northern Spain, but its exeligmos from July 10, 1972 passed over parts of Russia, Alaska and Northeast Canada. Ed Guinan, PhD, ’64 CLAS, professor of Astrophysics and Planetary Science, witnessed that one with a Villanova contingent on the Gulf of St. Lawrence in Nova Scotia. Fifty-four years from now, this eclipse will be only a partial one, as the saros series begins to wane. The upcoming August event, in fact, is the penultimate of 10 total solar eclipses in Saros 126. The 10th will be in August 2044—the next one visible in the contiguous United States, seen in totality in parts of Montana, North Dakota and South Dakota. Saros 126 began with a partial eclipse on March 10, 1179, and will end with another partial on May 3, 2459. Humans understood these patterns long before this one began. In the first millennium BCE, the Chaldeans discovered the saros cycle by “carefully keeping record of observations” of eclipses over time, explained Dr. Maloney. “Our lives are linked with the sun. To the ancients, having the sun disappear was believed to be a really bad thing, like a demon devouring it. That goes for lunar eclipses too, which caused the moon to turn red and really bother people. When they could begin to predict them, total eclipses ceased to be the powerfully bad omens that ancients believed they were. It was still a mystery as to why it happened, but at least it was predictable, which reduced people's anxieties.” Now, the anxiety stemming from eclipse viewing is saved for the fierce competition for hotels along the path of totality and threats of cloudy weather. “But don’t worry,” Dr. Maloney said. "If you miss one, you might be able to see it ‘nearby’ in another 54 years.”

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Ahead of America250, Villanova Historian Reveals How Independence Hall Almost Didn't Survive

Philadelphia’s Independence Hall has long occupied an outsized place in the American imagination. The space where the Continental Army was established, the Declaration of Independence adopted and the United States Constitution ratified, the site was once described by President Abraham Lincoln as the source “where were collected together the wisdom, the patriotism, the devotion to principle, from which sprang the institutions under which we live.” In July, these hallowed grounds will yet again take center stage, as the country observes its semiquincentennial, or America250, celebration. In due course, House lawmakers will gather at the landmark for a special commemorative event, mayors from across the U.S. will march to the gates in a show of civic pride and solidarity, and thousands of visitors will flock to the site daily in appreciation for its significance to the cause of “Life, Liberty and the pursuit of Happiness.” However, while Independence Hall’s role in the national saga will go widely remarked and recognized, the building itself has a story that remains largely unknown. According to Whitney Martinko, PhD, associate professor of History and director of the Albert Lepage Center for History in the Public Interest at Villanova University, the “cradle of American democracy” almost never survived the country’s infancy. “Early on, the challenge was about two things,” says Dr. Martinko, who specializes in public history, historic preservation and the early U.S. “One was about ownership of what was called the ‘Old State House,’ because it was the former statehouse in the colony of Pennsylvania. And the second was about the development of the city around it.” As Dr. Martinko explains, in the early 19th century, Independence Hall—then the Old State House—was under the control of the Commonwealth of Pennsylvania, which had shifted its governmental seat from Philadelphia to Harrisburg by 1812. To fund the construction of a new capitol building in the wake of the move, Pennsylvania legislators seriously contemplated selling the site to private enterprise, with the surrounding area undergoing a development boom. “Today’s Independence Mall was built up entirely,” says Dr. Martinko. “In the 18th century, it was full of buildings, shops and houses, and by the 19th century, it had become a huge furniture district and a heart of commerce in many ways.” As plans were drawn up to deliver the hall to the highest bidder, local resistance quickly emerged. Opposed to the landmark’s loss, citizens of Philadelphia and municipal leaders rushed to the defense of the building and its lawn, arguing that their preservation entailed a necessary public good. “Everyone looked to this site as the heart of the new nation. It’s a historic site. It’s an important building. 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