At 3 a.m. on a crisp May night in Chile, everything appeared normal with the world’s largest digital camera. Until it wasn’t.
Inside the Vera C. Rubin Observatory, project scientist Sandrine Thomas was running a routine check. Suddenly, the temperature gauge for the telescope’s camera went flat before spiking unexpectedly.
“That’s not good,” Thomas realized, and indeed, it wasn’t.
Alarmed, the scientists promptly shut down the telescope.
Hours later, I arrived, jet-lagged yet eager to see the observatory for the first time. Perched atop the flat-topped mountain Cerro Pachon, it gazes resolutely into the depths of space.
By scanning both widely and deeply, Rubin is capable of observing some of the slowest cosmic processes, like galaxies clustering or the universe’s expansion. Every few nights, it maps the entire southern sky, enabling the tracking of rapid events such as supernovae.
RubinObs/NSF/DOE/NOIRLab/SLAC/AURA, H. Stock Brand
Over the upcoming decade, Rubin plans to capture 2 million images. These telescopes possess the capability to observe more of the universe than any prior telescope. “For the first time in history, cataloged objects will outnumber the survivors!” the astronomers proclaimed in 2019.
Zeljko Ivezic from the University of Washington in Seattle, who dedicated decades to leading Rubin’s construction, was among them.
Many secrets lie hidden in the cosmos. “We need someone like Rubin to uncover those mysteries,” Ivezic emphasized. “There’s no competition.”
However, Thomas and her team first needed to bring the cameras back online.
From dark matter to asteroids
The concept for Rubin was born during yet another early morning vigil in 1996, near Cerro Pachon.
Astronomer Tony Tyson and his colleagues were testing a new camera at the summit of Cerro Tororo. This camera employed relatively innovative technology: charge-coupled devices or CCDs, which transform light particles, or photons, into electrons, subsequently producing images from the light source.
Various CCDs connected like patches on a quilt create a larger camera; the bigger the camera, the clearer the resulting images.
At that time, Tyson’s camera was unrivaled, featuring four CCDs designed to map dark matter—an elusive substance believed to constitute 80% of the universe’s mass. Despite its unseen nature, astronomers infer its existence due to its gravitational effects on visible objects. (One such effect inspired the name of the new observatory after astronomer Vera Rubin.)
During a night in the telescope’s control room, Tyson proposed, “We can do better.” He theorized that constructing larger CCD quilts could enhance telescopic imaging.
Advancements in computing were keeping pace, rapidly processing the influx of data.
Tyson embarked on developing this new observatory as his passion project.
“I dubbed it the dark matter telescope,” he recounts. Yet, its potential reached far beyond mapping dark matter; it could also explore “an entire universe of moving and exploding phenomena,” Tyson stated, envisioning asteroids racing towards Earth, stars pulsating, and black holes engulfing matter. This telescope is capable of scanning millions of objects within our solar system and billions of far-off galaxies.
By 2010, the astronomical community prioritized the project for U.S. government funding, and their aspirations were fulfilled. The observatory was set to become a reality.
Record setter
Rubin Observatory houses the current largest digital camera ever constructed. Weighing approximately 3,000 kilograms (6,600 pounds) and measuring 1.65 meters (5.4 feet) wide, it contains 189 CCDs, akin to the pixel count in a smartphone camera.
Additionally, Rubin is equipped with a set of massive and unique mirrors. Traditional telescopes begin with an 8.4-meter (27.5-ft) wide primary mirror that gathers light, which is then reflected to a secondary mirror measuring 3.5 meters (11.5 feet) wide. A third mirror corrects any distortion in the captured light.
A car-sized digital camera is suspended at the center of the secondary mirror. By the time light reaches this point, each facet appears as sharp as can be.
Rubin aims to capture the entire southern night sky every three to four days, with its camera shutter opening for 30 seconds per shot and achieving up to 1,000 images nightly. This routine will persist every night for ten years.
The sound of camera shutters can often be heard from the control room throughout the night.
Thomas finds this sound reassuring. “When it goes quiet, that’s when you need to worry,” she remarks.
A fun house mirror
Reaching Cerro Pachon involved flying into La Serena, a coastal city in Chile. A local driver transported me through the earthen-hued mountains. As the loud ride ascended higher, I noticed the telescope dome glowing in the distance, prompting laughter.
The elevated, arid location far removed from city lights renders it an ideal telescope site. The air felt so dry it parched my nostrils and throat. The visibility was extraordinary, and the terrain featured scattered rocks, scrubs, and occasional wild horses or viscachas (locally likened to a rabbit with a squirrel’s tail as per Thomas).
As the observatory remained under construction, we donned reflective yellow vests and helmets, some adorned with custom-made Vera Rubin stickers.
Having spent nearly a year anticipating this visit, arriving at the site was exhilarating. The telescope had just absorbed its first light a month prior and had been actively gathering data nightly. I was eager to witness its early complete images.
However, I came just eight hours post the camera’s temperature anomaly. The entire facility felt eerily still as Thomas escorted me on a tour.
Along the way, I spotted a camera crew. “Is my camera operational yet?” Thomas playfully inquired, exclaiming encouragement to her team. Turning to me, she added, “We’re trying to maintain optimism, but it’s a challenging time.”
Fortunately, I had a chance to glimpse the rare primary mirror, which looked oddly like a fun-house reflection. I swayed back and forth, crouched low, and gradually rose, watching how the shape transformed. It was a dizzying experience.
Keeping cool
The camera malfunction steered Thomas and her team to examine a critical aspect of the telescope’s design: temperature control.
Cameras must remain cool; excessive heat can lead the CCD to emit electrons, simulating light signals from cosmic entities.
A metal “cryoplate” positioned at -123 degrees Celsius (-189.4 degrees Fahrenheit) rests at the rear of the detector. Behind it lies another “cold” plate at -40 °C (-40 °F). Cooling lines channel coolant into the camera, while the dome’s exterior is crafted to reflect warmth away from the telescope.
Thomas and her team were eager to determine why the cryoplate suddenly escalated in temperature at 3 a.m. Rubin had been rigorously operational over the preceding month, marking its first crisis.
However, the ramifications extend beyond mere false photon detection. If the cryogenic casing warms, pressure may increase, causing internal materials to liberate gases capable of damaging the system.
This risk, while minimal, is indeed significant, as Sean McBride noted during my visit. “This ranks among the top five most alarming issues a camera can encounter,” he confessed.
McBride, based at the University of Zurich as a contract scientist for Rubin, is responsible for testing all telescope components and comprehending their functionality prior to data collection.
By afternoon, the camera appeared to return to its normal state. This offered a clue, Kevin Fanning commented, as Rubin’s contract scientists operate and work in Chile, under the auspices of the SLAC National Accelerator Laboratory.
As winter began in Chile, temperatures outside plummeted to 5 degrees Celsius (41 degrees Fahrenheit) for the first time since the camera installation. “It’s warmer today, and it seems like it has bounced back,” Fanning remarked.
Maybe the problem stemmed from the cold. But why did it heat the cryoplate? And what accounted for the critical threshold around 5 degrees Celsius? That remained puzzling, as “very few things change states at that temperature,” Fanning observed.
Fanning suggested an experiment to cool the dome down to 5 °C, to examine whether the cryoplate might malfunction again. The team awaited colder outdoor conditions, preparing to slightly open the dome for cold air. In the interim, UNO cards were enlisted for distraction.
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Eyes scanning the sky
“I feel personally slighted by the weather,” Fanning mused. Yet, by morning, he was uplifted. The cryoplate maintained its low temperature, suggesting the failure was indeed influenced by the outside cold.
Perhaps the coolant material had thickened sufficiently to hinder the cryoplate’s normal cooling. Accumulated water in the pipes could have frozen, leading to a blockage. Identifying where the external cold impacts the system will allow for enhanced insulation.
That night, the crew turned the camera back on, and by the following evening, observations resumed. Fanning indicated they were still probing the source of the glitch, while also planning to add insulation and introduce extra heat into the dome.
“It was a challenging weekend, but I’m thrilled with the strides we made and how the team collaborated to get back on course swiftly,” Fanning wrote in an email.
In June, the telescope achieved a significant milestone as the public could view Rubin’s inaugural image, showcasing 10 million galaxies and over 2,000 newly identified asteroids. As Rubin continues to observe the same region over time, more faint celestial objects emerge from the shadows.
About 90% of Rubin’s operational time is dedicated to exploring broad and profound aspects of the sky, with the capability to pivot quickly. For instance, if another telescope spots a supernova, Rubin can swing to that discovery for further observation.
Access to Rubin’s data is open to everyone, including students and amateur astronomers. “Your ideas, knowledge, and perseverance will dictate the science that is actually conducted,” asserts Ivezic.
Awakening of the Dragon
An hour prior to my departure in May, the crew opted to activate the telescope. Everyone hurried upstairs to the dome to witness it. Entering, I perceived the dome rotating, an experience akin to the ground shifting beneath me.
The dome felt cathedral-like, expansive, and circular; however, it was eerily quiet. The telescope occupied much of the space, with walls enveloped in sound-absorbing material designed to lessen stray light.
Fanning sat in a wheeled chair, laptop in hand, guiding the telescope through a series of movements to assess its range. “Please look up,” he directed, requesting a low-to-high pan and a circular sweep.
In motion, Rubin resembled an awakening dragon, displaying an elegance and speed that was remarkable. It tipped its head back, shifted its shoulders, turned its gaze skyward, and endeavored to open its “eyes.”
Source: www.snexplores.org
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