The Vera C. Rubin Observatory is ready to transform our understanding of the cosmos
High atop Chile’s 2,700-meter Cerro Pachón, the air is clear and dry, leaving few clouds to block the beautiful view of the stars. It’s here that the Vera C. Rubin Observatory will soon use a car-size 3,200-megapixel digital camera—the largest ever built—to produce a new map of the entire night sky every three days.
Generating 20 terabytes of data per night, Rubin will capture fine details about the solar system, the Milky Way, and the large-scale structure of the cosmos, helping researchers to understand their history and current evolution. It will capture rapidly changing events, including stellar explosions called supernovas, the evisceration of stars by black holes, and the whiz of asteroids overhead. Findings from the observatory will help tease apart fundamental mysteries like the nature of dark matter and dark energy, two phenomena that have not been directly observed but affect how objects in the universe are bound together—and pushed apart.
Rubin is the latest and most advanced entrant into the illustrious lineage of all-sky surveyors—instruments that capture, or survey, the entire sky, over and over again. Its first scientific images are expected later this year. In a single exposure, Rubin will capture 100,000 galaxies, the majority invisible to other instruments. A quarter-century in the making, the observatory is poised to expand our understanding of just about every corner of the universe.
The facility will also look far outside the Milky Way, cataloguing around 20 billion previously unknown galaxies and mapping their placement in long filamentary structures known as the cosmic web.
“I can’t think of an astronomer who is not excited about [Rubin],” says Christian Aganze, a galactic archeologist at Stanford University in California.
The observatory was first proposed in 2001. Then called the Large-Aperture Synoptic Survey Telescope (LSST), it grew out of an earlier concept for an instrument that would study dark matter, the enigmatic substance making up 85% of the matter in the universe. LSST was later reenvisioned to focus on a broader set of scientific questions, cataloguing the night sky over the course of a decade. Five years ago, it was renamed in honor of the late American astronomer Vera Rubin, who uncovered some of the best evidence in favor of dark matter’s existence in the 1970s and ’80s.
During operations, Rubin will point its sharp eyes at the heavens and take a 30-second exposure of an area larger than 40 full moons. It will then swivel to a new patch and snap another photo, rounding back to the same swath of sky after about three nights. In this way, it can provide a constantly updated view of the universe, essentially creating “this huge video of the southern sky for 10 years,” explains Anais Möller, an astrophysicist at the Swinburne University of Technology in Melbourne, Australia.
To accomplish its work, Rubin relies on an innovative three-mirror design unlike that of any other telescope. Its primary mirror is actually made up of two separate surfaces with different curvatures. The outer section, 8.4 meters wide, captures light from the universe and reflects it onto a 3.4-meter-wide secondary mirror located above it. This bounces the light back onto the inner part of the primary, which stretches five meters across and is considered a tertiary mirror, before being reflected into a digital camera. The compact configuration allows the enormous instrument to be powerful but nimble as it shifts around to take roughly 1,000 photos per night.
“It has five seconds to go to the next position and be ready,” says Sandrine Thomas, the deputy director for the observatory’s construction and project scientist for the telescope. “Meaning that it doesn’t move. It doesn’t vibrate. It’s just rock solid, ready to take the next image.”
Rubin’s 3,000-kilogram camera is the most sensitive ever created for an astronomical project. By stacking together images of a piece of sky taken over multiple nights, the telescope will be able to spot fainter and fainter objects, peering deeper into the cosmos the longer it operates.
Each exposure creates a flood of data, which has to be piped via fiber-optic cables to processing centers around the world. These use machine learning to filter the information and generate alerts for interested groups, says Möller, who helps run what are known as community brokers, groups that design software to ingest the nightly terabytes of data and search for interesting phenomena. A small change in the sky—of which Rubin is expected to see around 10 million per night—could point to a supernova explosion, a pair of merging stars, or a massive object passing in front of another. Different teams will want to know which is which so they can aim other telescopes at particular regions for follow-up studies.
With its capacity to detect faint objects, Rubin is expected to increase the number of known asteroids and comets by a factor of 10 to 100. Many of them will be objects more than 140 meters in diameter with orbits passing near Earth’s, meaning they could threaten our world. And it will catalogue 40,000 new small icy bodies in the Kuiper Belt, a largely unexplored region beyond Neptune where many comets are born, helping scientists better understand the structure and history of our solar system.
“We have never had such a big telescope imaging so wide and so deep.”
Anais Möller, astrophysicist, Swinburne University of Technology, Melbourne, Australia
Beyond our solar system, Rubin will see telltale flickers that signal exoplanets passing in front of their parent stars, causing them to briefly dim. It should also find thousands of new brown dwarfs, faint objects between planets and stars in size, whose positions in the Milky Way can provide insight into how the environments in which stars are born affect the size and type of objects that can form there. It will discover never-before-seen dim dwarf galaxies orbiting our own and look closely at stellar streams, remnant trails of stars left behind when the Milky Way tore other, similar galaxies apart.
The facility will also look far outside the Milky Way, cataloguing around 20 billion previously unknown galaxies and mapping their placement in long filamentary structures known as the cosmic web. The gravitational pull of dark matter directly affects the overall shape of this web, and by examining its structure, cosmologists will glean evidence for different theories of what dark matter is. Rubin is expected to observe millions of supernovas and determine their distance from us, a way of measuring how fast the universe is expanding. Some researchers suspect that dark energy—which is causing the cosmos to expand at an accelerated rate—may have been stronger in the past. Data from more distant, and therefore older, supernovas could help bolster or disprove such ideas and potentially narrow down the identity of dark energy too.
In just about every way, Rubin will be a monumental project, explaining the near-universal eagerness for those in the field to see it finally begin operations.
“We have never had such a big telescope imaging so wide and so deep,” says Möller. “That’s an incredible opportunity to really pinpoint things that are changing in the sky and understand their physics.”
Adam Mann is a freelance space and physics journalist who lives in Oakland, California.
