In an old experimental hall previously used for particle physics experiments, a team of French engineers is inspecting the filter of the largest digital camera ever. It's October 2021, and I saw the camera during assembly at the SLAC National Accelerator Laboratory in Menlo Park, California. When this high-resolution imager is finally put into use, it will provide us with stunning views of the depths of the universe.

The instrument is a traditional spatio-temporal survey (LSST) camera. This 3.2 gigapixel (3.2 billion pixels) camera will eventually be installed at the Vila Rubin Observatory on the top of a mountain in Chile, where it will take half of the southern sky every three days. Approximately once a week, it will provide astronomers, astrophysicists and cosmologists with a complete picture of the sky region.

Aaron Roodman, an astrophysicist and chief scientist of camera assembly and testing, told Gizmodo: "We will see something darker than what people have seen before in a certain area of ​​the sky." People have done very deep things, but they have been in tiny areas of the sky." The new telescope will be able to see long distances in a huge area-so it can also see the past.

The weekly portraits will collectively form the Space-Time Heritage Survey, a 10-year Southern Sky Survey that will collect data on the shape, position, and color of objects in space, including millions of stars and billions of galaxies. Images taken every 15 seconds will allow researchers to pay close attention to near-Earth asteroids, gain insight into the origin and evolution of the Milky Way, understand the nature of dark matter and dark energy, and possibly discover new phenomena in the universe.

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Steven Kahn, an astrophysicist and director of the Rubin Observatory, told Gizmodo: "The main purpose is to get as much sky as possible as quickly as possible, and to do so repeatedly." "The simplest thing it can do is to say, 'What has changed? How has it changed? We will do this on wazoo."

The regularity of camera images will effectively provide real-time understanding of near and far space events, thereby fully understanding how dynamic our universe is.

The LSST camera has six optical filters that rotate like a lazy Susan and can be swapped in and out according to the light conditions of a given night and the object the staff is trying to capture. The filter will enable the camera to image the sky in six different electromagnetic spectrum bands from the near ultraviolet to the near infrared.

Initially, the plan was to install the camera in Chile by 2014, but the production of the camera was hampered by delays, most recently due to covid-19. Rudman said that even without the challenge of the pandemic, managing such a large team of interdisciplinary scientists and engineers is "like grazing." But now things have finally come together.

"If there is no new crown virus, we will ship the same as a year ago," Khan said. "At this stage, since everything is very close to assembly, everything is critical."

The front of the camera consists of three lenses and the filters used. Very frank. But behind it is the crown jewel of the 5.5-foot-wide and 10-foot-long camera: its focal plane, which is the area where the light from the telescope’s mirror is cast.

The focal plane is composed of 189 charge-coupled devices (CCD), which are arranged in 21 groups of nine, all of which are cooled to close to -150°F in a vacuum to reduce noise in the image and increase the sensitivity of the camera. The top of each 2-foot long CCD has a square sensor that forms the focal plane. The focal plane is very flat, and the inclination in any direction will not exceed 10 microns. (A human hair is about 70 microns wide.) The CCD itself is basically a digital camera. They are grouped together in the form of nine rafts, capturing a mosaic image of the sky. It is this technology that will absorb all the light reflected from the three mirrors of the telescope.

Putting the focal planes together is a beast; a large number of CCDs need to be arranged very flat and very close together in an array, but they cannot actually touch to avoid damaging any of them. "If you have a gap, we are just wasting light. The stars will fall into that space, and then we won't be able to get the data," Kahn said, adding that putting the planes together is like parking a car with a gap of less than one centimeter. Luxury car. Roodman said that each raft is more expensive than Maserati, which makes assembly (in this clean room at SLAC) a stressful process. The team tested the full focal plane on the head of cauliflower last year.

Once it is in Chile, the camera will be located between three mirrors; one on the top and two on the bottom. The main mirror is 27.56 feet (8.4 meters) wide, and the tertiary mirror is 16.4 feet (5 meters) wide. According to the Rubin Observatory team, the secondary mirror between them is 11.2 feet (3.42 meters) wide, making it the largest convex mirror in history.

The focal plane will actually point to the ground to capture an image of space. The light from the night sky will be reflected from the lower mirror to the higher convex mirror, then back to the last mirror, and finally reflected into the camera.

I learned about this in the locker room of the SLAC National Accelerator Laboratory, where the engineers working there put on special booties and bunny suits in a custom clean room to avoid bringing any external dust or debris into the vicinity of the camera. This building was once used for antimatter research. Roodman said that when the Rubin Observatory team moved in, they had to dispose of a pile of "graves" of old instruments. The clean room is built in an experiment hall similar to a clothes rack, high enough to install a crane, which will insert a cryostat-a capsule that contains all the supercooled components and maintains these temperatures-and a trunk for the electronic components, most likely 2022 February.

One day, the camera will rotate back and forth, and a lot of data will be generated every night. But first it must ensure the safety of the Rubin Observatory. The plan is to send the camera to Chile in the late summer of 2022. Understandably, the team felt a lot of pressure on this trip. Last summer, they sent a rough camera alternative to Chile, called a large-scale alternative, to test the impact that delicate cameras must deal with during transportation. The agent looks a lot like a container, but has the same quality and center of gravity as the LSST camera. It is equipped with sensors to measure how much vibration it has experienced during the journey.

Kahn said: "Due to the new coronavirus, charter flights will be very expensive for large-scale surrogacy." "So we did a more commercial thing, but they will not leave San Francisco, they will only leave Miami, so We shipped it from the whole country to Miami. Then we flew it from Miami to Santiago, but God knows the reason for their stay in Brazil...It's not entirely representative."

"Well, it's worse," Rudman added. "So this is a good test."

The Rubin Observatory has four main scientific goals: the solar system and its surrounding millions of objects; the structure and formation of our home Milky Way; variable objects in the sky, such as cosmic explosions and other fleeting events; and In order to pay homage to its name and explore the nature of dark matter and dark energy, the former was observed by Vera Rubin through gravity in the mid-20th century.

Every night, the camera outputs 15 terabytes of data, including the brightness, position, shape, and color of objects it sees. The Rubin Observatory will send 10 million automatic alerts on the information contained therein every night. In the past, astronomers, astrophysicists, and cosmologists could rely on email updates and other notifications about new and interesting phenomena in space. "The real challenge is actually filtering these 10 million things every night," Kahn said. "How did you find the really unusual thing that distinguishes wheat from chaff?" Kahn said that to some extent, the filtering process will be automated. But the most advanced event will be able to be picked out and spread immediately, so other observatories around the world will be able to immediately turn to an interesting event. The more data from more instruments, the better.

In addition to the camera's huge resolution, its field of view (large enough to cover the space of a star with 40 full moons) will completely change the scientist's ability to choose the universe model. With such frequent images in such a vast sky, the team can effectively track the changes of a large number of objects over time. It is equivalent to a stop-motion animated movie of the observable universe (in the southern hemisphere).

It is particularly exciting to see some events with an ultra-sharp camera, such as lens events, which occur when light is bent by the gravitational field of a massive object. In a strong lens event, the light will be sharply bent around the object on its way to the earth, so that it arrives here at different times, resulting in a double or triple vision of the same light source. This is the case of the Requiem supernova. From our perspective, it flashed three times in 2016.

Dark matter seems to constitute a large part of the universe but is actually invisible mysterious matter, and is the natural target of the observatory.

"In my career, smart people realized,'Oh my God, there is a lot of dark matter in the universe," Oh, dark matter is more than ordinary matter,' and in fact, three-quarters of the matter is even in the universe. Not a problem. This is another matter. So, you know, researching is irresistible," Roodman said.

Scientists are not yet sure what is driving the accelerated expansion of the universe, or why it is calculated as a different number based on whether you measure the Hubble parameter with a close object or the cosmic microwave background.

"We have these big mysteries. But at the same time, we have a standard model of particle physics, and in fact a standard model of cosmology. They are very successful, very well tested, and very successful in terms of numbers. But They really don't make any sense," Kahn said. "However, some things must be correct, because these mathematical predictions simply cannot be achieved with such precision."

Unfortunately, the camera will have to deal with man-made pollution: that is, satellite constellations, such as SpaceX's Starlink, may appear in up to 30% of the images taken by the LSST camera. Passing satellites may obscure the data or even become their own misleading data points. The scientific team measuring potential astronomical damage wrote that the new camera “needs to enter the pristine, unpolluted night sky, which has been an inherent right of the inhabitants of the earth for thousands of years”.

Even with these challenges, LSST has the potential to drive some of the most exciting astrophysics discoveries in the coming decades. All the images it collects will be open to the public, which means that even if you are not an astrophysicist, you can enjoy the fascinating behavior of objects in the universe. The first light of the observatory is currently scheduled for January 2023 and will be fully operational in October. There are many unanswered questions about how the universe formed and continues to change, and this camera will help us find the answers.