Vera C. Rubin Observatory Releases Long-Awaited First Photos

At the summit of Cerro Pachón, the Chilean mountain home to the newly constructed Vera C. Rubin Observatory, fatigued yet focused scientists gather in the observatory’s control room. They’re monitoring the systems around the 8.4-meter telescope while waiting to troubleshoot a problem: The telescope’s camera is overheating. And it's May, just weeks before the observatory is set to release its first images to the public.

Those images, now unveiled during a June 23rd “first look” event, are just the beginning. Every three nights for the next 10 years, the fast-moving and unprecedentedly sensitive telescope will complete a scan of the Southern Hemisphere’s sky, generating 60 million gigabytes of data. Named for the astronomer Vera Rubin, well known for her discovery of firm evidence for dark matter, the observatory will generate survey images that consist of a exposures of 15 or 30 seconds, using six filters to cover the full visible range as well as near-infrared wavelengths (330–1080 nanometers).

Eventually, those scans will help create a time-lapse “movie” of the universe known as the Legacy Survey of Space and Time (LSST). Its goals include demystifying dark matter and dark energy, catching fast-moving or ever-changing objects in the night sky, and mapping the universe around us.

But taking these initial images is no small feat. Since construction began in 2015, highly customized components built in labs around the world have been coming together on the remote mountaintop, with technical problems solved on-site.

“The last month was a crazy month, working very hard,” Fernanda Urrutia, an astrophysicist working on Rubin’s education and public outreach team, tells me soon after I arrive at the summit. The scientists’ work during my visit is focused on trying to fix the cooling systems for the Rubin digital camera, the largest in the world.

The cooling systems have always been “the big pickle” for engineers working on the LSST Camera, says research engineer Claire Juramy (French National Institute of Nuclear and Particle Physics). Different parts of the camera need to be kept at different temperatures and, if any of their separate cooling systems malfunction, the camera can overheat relatively quickly. So, when on-site scientists saw the camera’s temperature climbing even as the outside air temperature dropped in the middle of the night, they were quick to shut it down and start problem-solving.

“Admittedly, there is not a good understanding of the situation today,” says Kevin Fanning, a member of the commissioning science and camera teams. But Fanning and the rest of the group on-site did not seem bogged down by this uncertainty — even so close to taking the first images. Shutting down the camera provides a great opportunity to conduct engineering tests they can’t do while actively observing the sky. “It’s definitely stressful, but I love these days,” Fanning added.

By evening, the temperature graphs on the screens in the summit control room are stabilizing, and engineers establish a plan for the night. They want to wait until the outside temperatures drop again before operating the camera, to determine if the cold air outside is responsible for the cooling system’s malfunction. This test is expected to be a slow one, and some of the observing scientists settle around to play Uno as night falls on the mountain.

But behind us, the many graphs on screen suggest the outside temperature is not falling at all — it's getting hotter. “Weather forecasts for mountaintops are notoriously difficult to do,” Fanning explains.

As it became clear they would have to wait another night to complete the test, the scientists recount the camera’s installation in March, when they had to place the camera at just the right place relative to the primary and secondary mirrors to capture in-focus images. “By dead reckoning, we placed this camera within maybe three millimeters [of where it should be],” says Robert Lupton, who works with scientific software at Rubin as the LSST’s pipeline scientist. But due to the very wide (3.5 degrees) field of view, if the camera is just slightly out of place, the engineering images turn up donuts of light where there should be stars. Commissioning images provided the information needed to tweak the camera’s placement until it was just right.

Slow and steady seems to do well as a guiding principle for the observatory. The same principle applies to fixing the cooling system, notes Aaron Roodman (Stanford University), who leads the camera team. “Take a step and then discuss,” he advises the others via video call the next morning as they formulate a new plan.

It turns out the cold night air was involved. In the following weeks, the team further insulates the cooling systems and explores heating options to keep parts of the camera warm on cold nights. The fixes bring the observatory one step closer to the first-look images.

Now, those images showcase the observatory’s potential. Wide fields that are an astounding 3.5° across focus on patches of sky full of galaxy clusters and nebulae, showing not only how deeply the camera can gaze into the universe but also giving a taste of how many objects there still are to discover and understand. The full survey of the Southern Hemisphere sky is slated to begin later this year.

In Chile, the celebrations are just one more step in the continuing collaborative process of getting the high-profile observatory up and running.

The reporting for this article was partially supported by a grant from the National Science Foundation.