A new observatory is assembling the most complete time-lapse record of the night sky ever
On 23 June 2025, the world will get a look at the first images from one of the most powerful telescopes ever built: the Vera C. Rubin Observatory.
Perched high in the Chilean Andes, the observatory will take hundreds of images of the southern hemisphere sky, every night for 10 years. In doing so, it will create the most complete time-lapse record of our Universe ever assembled. This scientific effort is known as the Legacy Survey of Space and Time (LSST).
Rather than focusing on small patches of sky, the Rubin Observatory will scan the entire visible southern sky every few nights. Scientists will use this rolling deep-sky snapshot to track supernovae (exploding stars), asteroids, black holes, and galaxies as they evolve and change in real time. This is astronomy not as a static snapshot, but as a cosmic story unfolding night by night.
At the heart of the observatory lies a remarkable piece of engineering: a digital camera the size of a small car and weighing over three tonnes. With a staggering 3,200 megapixels, each image it captures has enough detail to spot a golf ball from 25km away.
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Each image is so detailed that it would take hundreds of ultra-high-definition TV screens to display it in full. To capture the universe in colour, the camera uses enormous filters — each about the size of a dustbin lid — that allow through different types of light, from ultraviolet to near-infrared.
The observatory was first proposed in 2001, and construction at the Cerro Pachón ridge site in northern Chile began in April 2015. The first observations with a low-resolution test camera were carried out in October 2024, setting up the first images using the main camera, to be unveiled in June.
The observatory is designed to tackle some of astronomy's biggest questions. For instance, by measuring how galaxies cluster and move, the Rubin Observatory will help scientists investigate the nature of dark energy, the mysterious force driving the accelerating expansion of the Universe.
As a primary goal, it will map the large-scale structure of the Universe and investigate dark matter, the invisible form of matter that makes up 27% of the cosmos. Dark matter acts as the 'scaffolding' of the universe, a web-like structure that provides a framework for the formation of galaxies.
The observatory is named after the US astronomer Dr Vera Rubin, whose groundbreaking work uncovered the first strong evidence for dark matter – the very phenomenon this telescope will explore in unprecedented detail.
As a woman in a male-dominated field, Rubin overcame numerous obstacles and remained a tireless advocate for equality in science. She died in 2016 at the age of 88, and her name on this observatory is a tribute not only to her science, but to her perseverance and her legacy of inclusion.
Closer to home, Rubin will help find and track millions of asteroids and other objects that come near Earth – helping warn astronomers of any potential collisions. The observatory will also monitor stars that change in brightness, which can reveal planets orbiting them.
And it will capture rare and fleeting cosmic events, such as the collision of very dense objects called neutron stars, which release sudden bursts of light and ripples in space known as gravitational waves.
What makes this observatory particularly exciting is not just what we expect it to find, but what we can't yet imagine. Many astronomical breakthroughs have come from chance: strange flashes in the night sky and puzzling movements of objects. Rubin's massive, continuous data stream could reveal entirely new classes of objects or unknown physical processes.
But capturing this 'movie of the universe' depends on something we often take for granted: dark skies. One of the growing challenges facing astronomers is light pollution from satellite mega-constellations – a group of many satellites working together.
These satellites reflect sunlight and can leave bright streaks across telescope images, potentially interfering with the very discoveries Rubin is designed to make. While software can detect and remove some of these trails, doing so adds complexity, cost and can degrade the data.
Fortunately, solutions are already being explored. Rubin Observatory staff are developing simulation tools to predict and reduce satellite interference. They are also working with satellite operators to dim or reposition spacecraft. These efforts are essential – not just for Rubin, but for the future of space science more broadly.
Rubin is a collaboration between the US National Science Foundation and the Department of Energy, with global partners contributing to data processing and scientific analysis. Importantly, much of the data will be publicly available, offering researchers, students and citizen scientists around the world the chance to make discoveries of their own.
The 'first-look' event, which will unveil the first images from the observatory, will be livestreamed in English and Spanish, and celebrations are planned at venues around the world.
For astronomers, this is a once-in-a-generation moment – a project that will transform our view of the universe, spark public imagination and generate scientific insights for decades to come.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Noelia Noël does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
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The 4 biggest mysteries the new Vera Rubin Observatory could solve
On a mountaintop in Chile's sprawling Atacama Desert, a new telescope has turned its mechanical eyes to the heavens, stargazing with unprecedented intensity. The Vera C. Rubin Observatory will take hundreds of pictures, every night, for the next 10 years. Astronomers around the world are absolutely giddy over Rubin, which is named for the late astronomer who discovered evidence for the existence of dark matter. The observatory's mirrors will collect a tremendous amount of light, catching the glint of very faint, faraway objects. That light will be focused into the largest digital camera on the planet, a 3,200-megapixel camera the size of an SUV, capable of producing pictures from multiple wavelengths of light. Instead of focusing on one segment of sky for hours at a time, Rubin is designed to take in a wide field of view, swiveling every five seconds to stare at a new spot with minimal shakiness. Stitched together, the observations will produce unprecedented time-lapse views of the entire night sky from the Southern Hemisphere, revealing a lively universe. (Vera Rubin was the GOAT of dark matter) Rubin is scheduled to begin full operations later this year, after technicians complete some final testing. So where does one point a half-billion dollar telescope? Scientists predict that the observatory will discover millions of asteroids and comets, several million supernova, 17 billion stars in the Milky Way, 20 billion galaxies, and other astrophysical phenomena that may have never been detected before. Our cosmic cup runneth over. Other observatories, on the ground and in space, have granted us countless cosmic wonders, but no telescope has basked in the night sky quite like this before. One might wonder whether 10 million exploding stars is perhaps too many, and indeed, astronomers I spoke with about Rubin say they're a tad overwhelmed. "A hundred years ago, you went to the telescope, you took your data, maybe on a photographic plate, and you brought it home and locked it in your desk drawer," Pauline Barmby, an astronomer at Western University in Canada, says. There will be so much data "that we really have to come up with much different ways of analyzing it," Barmby says. Scientists are ready to sift through the observations, which could help solve some of astronomy's biggest mysteries, from the workings of the solar systems to the large-scale forces driving the future of the universe. Here are the four biggest mysteries the panoramic observatory will investigate. For the last decade, astronomers have pondered about a mystery that stands to completely rewrite science textbooks: Is there actually another planet in our solar system, something the size of Neptune, drifting in the darkness? Scientists refer to this hypothetical world as Planet Nine, and Rubin may settle the matter of its existence. (Pluto, you might have heard, no longer holds the title of the ninth planet in the solar system, having been reclassified, on the grounds of various astronomical definitions, as a dwarf planet in 2006.) The theory for Planet Nine arose out of observations of icy celestial bodies that orbit beyond Neptune, in a region called the Kuiper belt. A handful of these objects seem to be tracing unexpected orbits through space; something other than the sun's gravity appears to be influencing their movements. One explanation is the presence of a giant, unseen planet, exerting enough gravity to mold their orbital journeys. There are other explanations that could explain the strange orbits, from the extravagant (perhaps there's a tiny black hole out there, or evidence for a new theory of gravity), to the more mundane (maybe there's nothing odd about the orbits, and our picture of the Kuiper belt is just incomplete.) Existing telescopes aren't capable of spotting the faint glow of such a faraway maybe-planet. But Rubin may find Planet Nine within the first year or two operations, says Megan Schwamb, an astronomer at Queen's University, Belfast, in Northern Ireland. Scientists have worked out a search area in the night sky. If the planet is there, "we'll see it like we see Pluto," Schwamb says—a bright pinprick in the inky shadows of the Kuiper belt, reflecting the light of its star. If there's no grand X-marks-the-spot moment for Planet Nine, "that doesn't mean it's not there," Samantha Lawler, an astronomer at Campion College in Canada, says. "It could just be farther out, or it could be smaller or less reflective." Astronomers will need to keep scrutinizing the behavior of trans-Neptunian objects, and Rubin is poised to discover 37,000 trans-Neptunian objects, expanding the current catalog tenfold. In a sea of these newly found celestial bodies, convincing evidence of Planet Nine may float to the surface, or become washed away altogether. While Schwamb and Lawler would be delighted to welcome a new planet, they're thrilled at the prospect of learning more about the realm beyond Neptune, which is intriguing in its own right. The frozen objects in the Kuiper belt are remnants of the formation of our cosmic neighborhood, like eraser shavings brushed off to the side of the page, and astronomers can study them to better understand its bygone eras. "I have no doubt there will be other weird patterns that we see in those orbits that will lead to other interesting ideas about what may or may not be in our solar system now, and how it has changed over time," Lawler says. In 2017, a ground-based telescope in Hawaii caught an unusual object hurtling through the solar system, untethered from the gravity of the sun. Oumuamua, as the object was later named, left astronomers with many questions about a previously undiscovered cosmic population, and some wild conjectures about alien origins that are still floating around today. A second surprise object, named Borisov, showed up in 2019, further deepening the mystery. Rubin will provide many more opportunities to study these interstellar objects, which can coast through the galactic hinterlands for hundreds of millions of years before encountering the warmth of a star. These objects appear without warning, and move fast, so they can be difficult to catch—unless you're constantly making time lapses of the night sky. Interstellar objects are believed to be ejected from their home systems during planet formation, a notoriously turbulent time. (Bits of our own solar system, hurled away several billions of years ago, are likely floating somewhere in the galaxy.) Some researchers estimate that Rubin, over the course of its decade-long run, may discover between five and 50 interstellar objects. Chris Lintott, an astrophysicist at Oxford, is more optimistic, betting on 100. It's quite the range, which underscores just how new, and exciting, this area of study is. Each time Rubin detects an interstellar object, it will spark a frenetic chase: telescopes around the world and in space will track the target until it zooms out of reach, checking to see how it's moving, what it's made of, and—because why not?—whether it bears signs of artificial technology. Each cosmic wanderer Rubin finds will provide a glimpse of how planet formation may have unfolded across the Milky Way. Are giant planets like Jupiter, Saturn, and Uranus common around other stars? Rubin's interstellar catch of the day could help answer that question. Or its findings could indicate these types of planets are rarer than we thought. "If we find very few [interstellar objects], I think we might have to rethink what sort of planetary systems exist in the galaxy," Lintott says. Even with the powerful new observatory, astronomers likely won't be able to trace interstellar objects to their exact starting points "because they've been mixed around the galaxy so much," says Michele Bannister, a planetary astronomer at the University of Canterbury in New Zealand. But they can analyze their chemical composition to glean information about their home star, including its age. Scientists may even be able to determine if two or more interstellar objects originated from the same cluster of stars. And they can use Rubin's future catalog to test various theories, including whether entire corridors of these interstellar objects exist, winding through the galaxy like ribbons. Even a small sample of them "tells us so much about these processes happening across our whole wonderful, wide galaxy," Bannister says. Galaxies form in a messy process, says Barmby, the Western University astronomer. "There's gas falling in, there's gas getting blown out, there's stars forming, there's stars dying, and all of that stuff happens on super-long timescales that we can't actually watch happen." Sometimes, in the process, stars in one galaxy get taken up by the gravitational force of another. These are known as stellar streams, and the new observatory is expected to reveal many more of these in our own Milky Way, hovering like bees around the shimmering rose of the galaxy. Rubin's observations will allow astronomers to track the motions of individual stars over long periods of time, which can reveal whether they originated inside the Milky Way or came tumbling in from a nearby galaxy. Rubin is also expected to discover more of the small galaxies that orbit the Milky Way, which have unwillingly donated some of those stars. Each galaxy has its own fascinating cosmic personality; one of the smallest has just a few hundred stars, compared to the Milky Way's 10 billion, says Yao-Yuan Mao, an astrophysicist at the University of Utah. He expects that Rubin will discover all the little galaxies that can possibly be observed, not counting those that are situated behind the bright disk of the Milky Way, which will remain forever out of view from Earth's perspective. "We will get a super complete picture of our Milky Way system," Mao says. And by comparing our galaxy system with that of others, astronomers can tackle one of the most animating questions in the field: whether the way the cosmos works here, in our part of it, is the same as everywhere else. "The knowledge that we inferred from studying the Milky Way—is that generally applicable across the universe?" Mao says. "Or is there something special or unique about the Milky Way itself?" As Rubin captures pictures of millions of cosmic objects, the observatory will also be searching for signs of two completely invisible things: dark matter and dark energy. All of the stars, galaxies, gas—all of the matter we can observe—turns out to be just 5 percent of "the total stuff in the universe," says Alex Drlica-Wagner, an astrophysicist at the University of Chicago. The rest is dark matter, a kind of matter that doesn't emit or absorb light, which accounts for 25 percent of the universe's composition, and dark energy, a phantom entity that makes up 70 percent. While scientists have never directly observed either, they've seen the cosmos behaving in certain ways that suggest they must exist. Rubin won't reveal all of their secrets, but the sheer amount of data will serve as a veritable playground for scientists to test their theories about these phenomena. Astronomers first suspected the existence of dark matter in the 1930s when they noticed that some galaxies remained clustered together even though they were traveling fast enough to fly apart, suggesting that another force was keeping the galactic web intact. In the 1970s, Rubin's namesake astronomer discovered a similar effect at the edges of galaxies, where whizzing stars that should have escaped were instead being held tight. The mark of the unseen material can even be found using starlight itself. Dark matter can bend light as it passes by, making its source—a distant galaxy, for example—appear distorted. Rubin will collect these warped views, allowing astronomers to "map out where the dark matter is by how we see the light bending as it travels to us," Drlica-Wagner says. Those maps can help illuminate the nature of dark-matter particles, including whether they're cold or hot—seemingly small characteristics with the capacity to reshape our understanding of how the universe assembles galaxies. Dark energy is even more mysterious. The idea emerged in the 1990s, when astrophysicists calculated that the universe was expanding faster over time rather than slowing down, which ran counter to laws of physics that governed the rest of the cosmos. Dark energy was determined to be the driving force, although scientists don't know what it actually is, only that it appears to behave differently than anything else in the universe, Drlica-Wagner says. Unlike dark matter, which, like the regular cosmic stuff, is likely made up of some kind of particles, dark energy stretches the very fabric of space, pushing galaxies apart rather than drawing them together. Rubin's massive catalog of exploding stars will come in handy here: Scientists can use certain kinds of supernovas to trace the universe's expansion, and, in turn, dark energy's role in it. Rubin data could confirm or refute new theories that suggest dark energy is changing over time, rather than remaining constant, upending even Einstein's predictions for this perplexing force. In the end, the most exciting discoveries Rubin makes might be the ones astronomers haven't yet anticipated. Such is the nature of really good new telescopes: the thrill of what we don't know we don't know. "If someone says, I have never seen a six-foot-tall-rabbit, you can say, sure, how hard have you looked?" Michael Wood-Vasey, an astronomer at the University of Pittsburgh who has spent years helping to prepare the Rubin observatory for operations, says. Perhaps the new observatory, with its constant, scouring gaze, will turn up some cosmic rabbits.
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National Geographic
4 hours ago
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The 4 biggest mysteries the new Vera Rubin Observatory could solve
No telescope has basked in the night sky quite like this before. Here's what it could reveal about the universe. Vera Rubin Observatory, its dome reflecting the last sunlight at sunset in Chile. May 30, 2025. Photographs by Tomás Munita On a mountaintop in Chile's sprawling Atacama Desert, a new telescope has turned its mechanical eyes to the heavens, stargazing with unprecedented intensity. The Vera C. Rubin Observatory will take hundreds of pictures, every night, for the next 10 years. Astronomers around the world are absolutely giddy over Rubin, which is named for the late astronomer who discovered evidence for the existence of dark matter . The observatory's mirrors will collect a tremendous amount of light, catching the glint of very faint, faraway objects. That light will be focused into the largest digital camera on the planet, a 3,200-megapixel camera the size of an SUV, capable of producing pictures from multiple wavelengths of light. Instead of focusing on one segment of sky for hours at a time, Rubin is designed to take in a wide field of view, swiveling every five seconds to stare at a new spot with minimal shakiness. Stitched together, the observations will produce unprecedented time-lapse views of the entire night sky from the Southern Hemisphere, revealing a lively universe. The Vera Rubin Observatory will offer an unprecedented view of the universe's wonders. Chile's new Vera Rubin Observatory, May 31, 2025. Rubin is scheduled to begin full operations later this year, after technicians complete some final testing. So where does one point a half-billion dollar telescope? Scientists predict that the observatory will discover millions of asteroids and comets, several million supernova, 17 billion stars in the Milky Way, 20 billion galaxies, and other astrophysical phenomena that may have never been detected before. Our cosmic cup runneth over. Other observatories, on the ground and in space, have granted us countless cosmic wonders, but no telescope has basked in the night sky quite like this before. One might wonder whether 10 million exploding stars is perhaps too many, and indeed, astronomers I spoke with about Rubin say they're a tad overwhelmed. "A hundred years ago, you went to the telescope, you took your data, maybe on a photographic plate, and you brought it home and locked it in your desk drawer," Pauline Barmby, an astronomer at Western University in Canada, says. There will be so much data "that we really have to come up with much different ways of analyzing it," Barmby says. Scientists are ready to sift through the observations, which could help solve some of astronomy's biggest mysteries, from the workings of the solar systems to the large-scale forces driving the future of the universe. Here are the four biggest mysteries the panoramic observatory will investigate. The Milky Way is seen above the observatory's Simonyi Survey Telescope. For the last decade, astronomers have pondered about a mystery that stands to completely rewrite science textbooks: Is there actually another planet in our solar system, something the size of Neptune, drifting in the darkness? Scientists refer to this hypothetical world as Planet Nine , and Rubin may settle the matter of its existence. (Pluto, you might have heard , no longer holds the title of the ninth planet in the solar system, having been reclassified, on the grounds of various astronomical definitions, as a dwarf planet in 2006.) The theory for Planet Nine arose out of observations of icy celestial bodies that orbit beyond Neptune, in a region called the Kuiper belt. A handful of these objects seem to be tracing unexpected orbits through space; something other than the sun's gravity appears to be influencing their movements. One explanation is the presence of a giant, unseen planet, exerting enough gravity to mold their orbital journeys. Deputy Observing Specialist Manager Alysha Shugart commands the TMA and Dome from platform 8 at the observatory. The M3 inner mirror, outer M1 mirror and LSST Camera of Simonyi's Survey Telescope at Vera Rubin Observatory, Chile. May 30, 2025. There are other explanations that could explain the strange orbits, from the extravagant (perhaps there's a tiny black hole out there , or evidence for a new theory of gravity ), to the more mundane (maybe there's nothing odd about the orbits, and our picture of the Kuiper belt is just incomplete.) Existing telescopes aren't capable of spotting the faint glow of such a faraway maybe-planet. But Rubin may find Planet Nine within the first year or two operations, says Megan Schwamb , an astronomer at Queen's University, Belfast, in Northern Ireland. Scientists have worked out a search area in the night sky. If the planet is there, "we'll see it like we see Pluto," Schwamb says—a bright pinprick in the inky shadows of the Kuiper belt, reflecting the light of its star. Enormous cables on Level 5, beneath the Telescope Mount Assembly (TMA), at the Vera Rubin Observatory, Chile. The Simonyi Survey Telescope at Vera Rubin Observatory, Chile. May 30, 2025. If there's no grand X-marks-the-spot moment for Planet Nine, "that doesn't mean it's not there," Samantha Lawler , an astronomer at Campion College in Canada, says. "It could just be farther out, or it could be smaller or less reflective." Astronomers will need to keep scrutinizing the behavior of trans-Neptunian objects, and Rubin is poised to discover 37,000 trans-Neptunian objects, expanding the current catalog tenfold. In a sea of these newly found celestial bodies, convincing evidence of Planet Nine may float to the surface, or become washed away altogether. While Schwamb and Lawler would be delighted to welcome a new planet, they're thrilled at the prospect of learning more about the realm beyond Neptune, which is intriguing in its own right. The frozen objects in the Kuiper belt are remnants of the formation of our cosmic neighborhood, like eraser shavings brushed off to the side of the page, and astronomers can study them to better understand its bygone eras. "I have no doubt there will be other weird patterns that we see in those orbits that will lead to other interesting ideas about what may or may not be in our solar system now, and how it has changed over time," Lawler says. Among the questions that the Vera Rubin Observatory could help answer: Is there a Planet 9? Scientists hope that the observatory can help map the universe's dark matter. In 2017, a ground-based telescope in Hawaii caught an unusual object hurtling through the solar system, untethered from the gravity of the sun. Oumuamua , as the object was later named, left astronomers with many questions about a previously undiscovered cosmic population, and some wild conjectures about alien origins that are still floating around today. A second surprise object, named Borisov , showed up in 2019, further deepening the mystery. Rubin will provide many more opportunities to study these interstellar objects, which can coast through the galactic hinterlands for hundreds of millions of years before encountering the warmth of a star. These objects appear without warning, and move fast, so they can be difficult to catch—unless you're constantly making time lapses of the night sky. Rubin Observatory's Simonyi Survey Telescope during calibration. Interstellar objects are believed to be ejected from their home systems during planet formation, a notoriously turbulent time. (Bits of our own solar system, hurled away several billions of years ago, are likely floating somewhere in the galaxy.) Some researchers estimate that Rubin, over the course of its decade-long run, may discover between five and 50 interstellar objects. Chris Lintott, an astrophysicist at Oxford, is more optimistic, betting on 100. It's quite the range, which underscores just how new, and exciting, this area of study is. Each time Rubin detects an interstellar object, it will spark a frenetic chase: telescopes around the world and in space will track the target until it zooms out of reach, checking to see how it's moving, what it's made of, and—because why not?—whether it bears signs of artificial technology. Each cosmic wanderer Rubin finds will provide a glimpse of how planet formation may have unfolded across the Milky Way. Are giant planets like Jupiter, Saturn, and Uranus common around other stars? Rubin's interstellar catch of the day could help answer that question. Or its findings could indicate these types of planets are rarer than we thought. "If we find very few [interstellar objects], I think we might have to rethink what sort of planetary systems exist in the galaxy," Lintott says. Even with the powerful new observatory, astronomers likely won't be able to trace interstellar objects to their exact starting points "because they've been mixed around the galaxy so much," says Michele Bannister, a planetary astronomer at the University of Canterbury in New Zealand. But they can analyze their chemical composition to glean information about their home star, including its age. Scientists may even be able to determine if two or more interstellar objects originated from the same cluster of stars. And they can use Rubin's future catalog to test various theories, including whether entire corridors of these interstellar objects exist, winding through the galaxy like ribbons. Even a small sample of them "tells us so much about these processes happening across our whole wonderful, wide galaxy," Bannister says. From interstellar objects to galaxy formation, the new telescope will give astronomers a stunning new view of deep space. The Vera Rubin Observatory is named for the pioneering scientist who explored the mysteries of dark matter. Petr Kubánek, right, and Robinson Godoy Torres checking on actuators and valves inside the M1M3 mirror cells of the Simonyi Survey Telescope, Vera Rubin Observatory, Chile. May 30, 2025, Galaxies form in a messy process, says Barmby, the Western University astronomer. "There's gas falling in, there's gas getting blown out, there's stars forming, there's stars dying, and all of that stuff happens on super-long timescales that we can't actually watch happen." Sometimes, in the process, stars in one galaxy get taken up by the gravitational force of another. These are known as stellar streams, and the new observatory is expected to reveal many more of these in our own Milky Way, hovering like bees around the shimmering rose of the galaxy. Rubin's observations will allow astronomers to track the motions of individual stars over long periods of time, which can reveal whether they originated inside the Milky Way or came tumbling in from a nearby galaxy. Rubin is also expected to discover more of the small galaxies that orbit the Milky Way, which have unwillingly donated some of those stars. Each galaxy has its own fascinating cosmic personality; one of the smallest has just a few hundred stars, compared to the Milky Way's 10 billion, says Yao-Yuan Mao , an astrophysicist at the University of Utah. He expects that Rubin will discover all the little galaxies that can possibly be observed, not counting those that are situated behind the bright disk of the Milky Way, which will remain forever out of view from Earth's perspective. "We will get a super complete picture of our Milky Way system," Mao says. And by comparing our galaxy system with that of others, astronomers can tackle one of the most animating questions in the field: whether the way the cosmos works here, in our part of it, is the same as everywhere else. "The knowledge that we inferred from studying the Milky Way—is that generally applicable across the universe?" Mao says. "Or is there something special or unique about the Milky Way itself?" Observing Specialist Minhee Hyun, left, and Yijung Kang at the Control Room of Vera Rubin Observatory, Chile. May 30, 2025. As Rubin captures pictures of millions of cosmic objects, the observatory will also be searching for signs of two completely invisible things: dark matter and dark energy. All of the stars, galaxies, gas—all of the matter we can observe—turns out to be just 5 percent of "the total stuff in the universe," says Alex Drlica-Wagner , an astrophysicist at the University of Chicago. The rest is dark matter, a kind of matter that doesn't emit or absorb light, which accounts for 25 percent of the universe's composition, and dark energy, a phantom entity that makes up 70 percent. While scientists have never directly observed either, they've seen the cosmos behaving in certain ways that suggest they must exist. Rubin won't reveal all of their secrets, but the sheer amount of data will serve as a veritable playground for scientists to test their theories about these phenomena. Astronomers first suspected the existence of dark matter in the 1930s when they noticed that some galaxies remained clustered together even though they were traveling fast enough to fly apart, suggesting that another force was keeping the galactic web intact. In the 1970s, Rubin's namesake astronomer discovered a similar effect at the edges of galaxies, where whizzing stars that should have escaped were instead being held tight. The mark of the unseen material can even be found using starlight itself. The observatory's telescope will be the largest digital camera on the planet, a massive 3,200-megapixel camera. Dark matter can bend light as it passes by, making its source—a distant galaxy, for example—appear distorted. Rubin will collect these warped views, allowing astronomers to "map out where the dark matter is by how we see the light bending as it travels to us," Drlica-Wagner says. Those maps can help illuminate the nature of dark-matter particles, including whether they're cold or hot—seemingly small characteristics with the capacity to reshape our understanding of how the universe assembles galaxies. Dark energy is even more mysterious. The idea emerged in the 1990s, when astrophysicists calculated that the universe was expanding faster over time rather than slowing down, which ran counter to laws of physics that governed the rest of the cosmos. Dark energy was determined to be the driving force, although scientists don't know what it actually is, only that it appears to behave differently than anything else in the universe, Drlica-Wagner says. Unlike dark matter, which, like the regular cosmic stuff, is likely made up of some kind of particles, dark energy stretches the very fabric of space, pushing galaxies apart rather than drawing them together. Rubin's massive catalog of exploding stars will come in handy here: Scientists can use certain kinds of supernovas to trace the universe's expansion, and, in turn, dark energy's role in it. Rubin data could confirm or refute new theories that suggest dark energy is changing over time, rather than remaining constant, upending even Einstein's predictions for this perplexing force. The observatory is expected to return so much data, scientists are preparing to be overjoyed—and perhaps overwhelmed. In the end, the most exciting discoveries Rubin makes might be the ones astronomers haven't yet anticipated. Such is the nature of really good new telescopes: the thrill of what we don't know we don't know. "If someone says, I have never seen a six-foot-tall-rabbit, you can say, sure, how hard have you looked?" Michael Wood-Vasey, an astronomer at the University of Pittsburgh who has spent years helping to prepare the Rubin observatory for operations, says. Perhaps the new observatory, with its constant, scouring gaze, will turn up some cosmic rabbits.
