Amundsen-Scott South Pole Station sits at an elevation of almost 2 miles or 3.2 kilometers. The altitude, as well as the cold, dry air often makes it difficult to breathe when exercising or performing manual labor. But these same conditions make the South Pole the best spot in the world to observe microwaves from outer space. The high altitude means the atmosphere is thin and the extreme cold freezes out any water vapor in the air. This is important because water absorbs microwaves, as well as emitting radiation that could be confused with cosmic signals. Since the Sun only rises and sets once a year at the South Pole, the atmosphere is very stable. During the long polar night, the Sun does not interfere with observations. Perhaps the single drawback is that only the southern celestial sky can be observed.
Constructed during the austral summer season between November 2006 and February 2007, the South Pole Telescope or SPT achieved “first light” (when the first signal was received through the telescope) on 16 February 2007 and began science observations the following month. SPT consists of a 10 meter (33 foot) dish with a surface accurate 25 micrometers or 1/1000thof an inch that collects signals in the microwave, millimeter-wave, and submillimeter-wave regions of the electromagnetic spectrum. The signals collected by the primary antenna or “mirror” are then reflected off a secondary mirror and finally arrive at a focal point on the sensors in a special camera that has been cooled to with one-quarter of a degree of absolute zero. Cooling is done with special “refrigerators” or heat pumps that use sound waves to compress and expand helium gas to achieve these incredibly low temperatures. Like something out of a science fiction movie, the sound produced by the acoustic heat pumps is appropriately out of this world.
The “film” in the camera consists of hundreds of temperature sensors or bolometers that are able to take the temperature of the universe. These temperature sensors are superconducting “transition edge sensors” (TES) that take advantage of the change in electrical resistance as the sensor transitions for being a normal electrical conductor (with resistance) to a superconductor (with zero resistance). The current camera is able to measure the polarization of incoming light with 780 polarization-sensitive pixels, each with two TES bolometers. They observe cosmic microwaves at frequencies of 90 GHz and 150 GHz.
The telescope and its camera were designed to study the Cosmic Microwave Background or CMB. The first survey performed by SPT of the southern sky was with a camera designed to find distant clusters of galaxies using the CMB as a “backlight” and succeeded in finding hundreds of galaxy clusters. The capabilities of the telescope can be modified by replacing the camera. The current camera is designed to detect the polarization of the incoming light and has many more sensors than previous cameras.
Most people are familiar with the concept of polarized light from having worn polarized sunglasses to reduce glare. As previously mentioned, the current camera attached to SPT is able to determine polarization. Polarized light from the CMB is predominately “E-mode” or the primordial light from the creation of the universe. The much scarcer “B-mode” polarized light is produced when the primordial light is exposed to extremely strong gravitational fields and is altered by gravitational lensing, the bending of light by strong gravitational fields functioning in much the same manner as an optical lens. This is important in understanding how the universe became what it is today. SPT is also helping to understand the nature of dark matter and dark energy, the main constituents of the universe.
It is interesting to note that some believe the true (clandestine) purpose of SPT is to secretly track the mysterious Planet X. This supposed planet is on a near collision course with Earth and returns every 3600 years with near calamitous results, such as the destruction of the Lost Continent of Atlantis on its last visit. This story is eerily familiar to that of one of my favorite science fiction films, The Man From Planet X, which is about a dying planet on a near collision course with Earth whose inhabitants plan to invade and colonize our world.
On another note as can be seen from the picture below, the sun is gradually returning to the South Pole. As one who has endured a long, cold, and dark winter, the Sun’s return can happen none too soon!