THE AMUNDSEN-SCOTT SOUTH POLE STATION IN ANTARCTICA, home of the South Pole Telescope, is one of the best places on Earth to catch faint microwaves coming from deep space. The high altitude (2,835 m) and extremely low humidity mean there is very little interference from light-absorbing water vapour in the atmosphere, so it’s ideal for astronomers studying the origins of the universe, who are looking for the faintest microwaves coming from deep space.
Matt Young is a PhD student at the Dunlap Institute for Astronomy & Astrophysics who hails from Australia and who has been supported by an Arts & Science International Graduate Scholarship. He spent two months at the South Pole, performing a crucial upgrade on the telescope’s camera while enjoying the balmy -30°C summer weather and 24-hour sunlight. He sent back these reports via the Dunlap Institute’s blog.
We arrived at the South Pole late on November 28, with the sun still high in the sky. (It never sets during the summer!) First off, we were given tips by the station doctor, with each tip being DRINK LOTS OF WATER. Thanks to the high altitude and extremely low humidity, dehydration is a major risk while you acclimatize. Even after drinking multiple litres of water, I spent the first day in bed with a splitting headache that even painkillers couldn’t fix. It took almost a week before I felt like I wasn’t on the verge of a serious hangover.
Each day we walk out to the Dark Sector Laboratory, the building where the South Pole Telescope is located, about one kilometre from the station. “Dark” just means that radio use is restricted due to potential interference with the experiments. At this time of year, it never actually gets dark.
We are working on the SPT-3G camera, which focuses and images the microwave light reflected from the telescope’s mirrors. The camera weighs over a tonne, so we first needed to carefully lower it from the optics bench that couples it to the telescope’s dish. Once it was on the floor, we could finally begin the long process of disassembly and reassembly.
The SPT-3G camera looks surprisingly like a gigantic DSLR. This is because the design is actually very similar: a long cylindrical section containing lenses focussing the light, and a rectangular section at the back containing detectors for measuring the light.
SPT-3G measures microwave light in three different bands: 90 GHz, 150 GHz and 220 GHz, each requiring its own lens. Over the past year some major advancements have been made in anti-reflective coatings, requiring us to replace the lenses. At almost one metre in diameter, each lens is made of heavy alumina. And even though they look opaque, they are almost completely transparent to the microwaves we want to measure, and function the same way that glass lenses do in an optical camera.
But the biggest upgrade this year is the installation of 10 new detector wafers. Each contains around 270 pixels, with each pixel able to measure microwaves in three different bands and two polarisations.
Another grad student and I spent a week holed up in our little clean room, assembling each of the 10 detector wafers, using tweezers to carefully place hundreds of tiny 0-80 screws. This work is not for the faint of heart: a single screw dropped onto a wafer can potentially wipe out hundreds of detectors (or worse, crack the wafer).
Once we finished assembling the wafers, we were ready to start installing them back into the focal plane—a slow and delicate process, where a broken connection in any of the 120 striplines could potentially force us to take everything apart for repairs. Finally, the camera focal plane was ready to be re-installed, with the help of four chain hoists and an engine jack.
In the first week of January, we finally achieved “first light” with the upgraded camera. That means we successfully installed it back onto the telescope, and the detectors were responding to light from astronomical objects, such as planets and star-forming regions.
One of the primary goals of the South Pole Telescope is to measure light from the Cosmic Microwave Background (CMB), radiation left over from the Big Bang. The universe began its life far denser and hotter than it is today, a primordial soup of light and particles. Almost 400,000 years after the Big Bang, as the universe expanded and cooled, this primordial light ceased interacting with particles and began to travel freely throughout the cosmos. This is the light we see today as the Cosmic Microwave Background, giving us a valuable tool for probing the conditions of the early universe.
Soon the camera will begin to survey a large patch of sky, measuring about 1,500 square degrees (almost 4 percent of the entire sky). The goal of this survey is to map out tiny fluctuations in the CMB temperature—changes that are smaller than one part in 100,000, like measuring centimetre-high waves on a kilometre-deep ocean. Thanks to the large 10-metre dish on the telescope, SPT-3G can map out these tiny fluctuations better than any other microwave telescope. This makes SPT well suited to particular science goals, such as measuring the bending of light throughout cosmic history, which tells us a lot about the growth of structure in the universe.
I flew out of the South Pole on January 17 with four other members of the SPT team, replaced by several fresh SPT-ers to take our place and continue working on the telescope until the end of the summer season. Following the last flight out of the station in mid-February, we then leave everything in the very capable hands of the SPT winter-overs, who are maintaining the telescope in freezing 24-hour darkness until next Austral summer.
TOP: Photo courtesy of Prof. Keith Vanderlinde; U.S. National Science Foundation.
BOTTOM: Matt Young in Antarctica. Photo courtesy of Matt Young.