The Cosmic Microwave Background (CMB) is light from the early universe that holds secrets of how the Universe was formed. Analyzing data from the CMB helps astrophysicists refine different models about the evolution of the Universe. In particular, astrophysicists focus on the microwave photon radiation of the CMB – electromagnetic radiation with wavelengths 1000 times longer than visible light. The light from the CMB encounters many different galaxies in its journey to our detectors, and this allows us to see how galaxies formed at the beginning of the Universe. For astrophysicists to come to these inferences about the evolution of the Universe and the early formation of galaxies, the CMB map must be as accurate as possible. Maps of the CMB are made from very careful measurements of temperature fluctuations of the Universe. The temperature of the CMB averages 2.726 Kelvin. This is because the Universe is not uniformly dense. Less dense regions correspond to colder temperatures and denser regions correspond to hotter ones. These fluctuations in temperature are minute, and thus require extremely precise telescope measurements.
The Atacama Cosmology Telescope (ACT) is a microwave telescope on Cerro Toco in the Atacama Desert of northern Chile. Its location in an arid desert allows the telescope to see the microwaves from the CMB relatively unaffected by the Earth’s atmosphere. Unlike optical telescopes, which take images, ACT moves rapidly across one strip of sky using temperature sensitive detectors collecting data about temperature fluctuations. ACT data is precise enough to make maps with noise levels that are at 1 part per million of the average microwave temperatures, and sensitive enough to detect temperature fluctuations within a millionth of a degree on the sky in different directions. Unfortunately, not all data from ACT is useable. ACT has around 3000 detectors that are continuously collecting data (2000 times per second). That is roughly a large book printed every second. These detectors are made of superconducting material which must stay cool in order to perform efficiently. When one detector goes bad the entire row of detectors can be affected. When a detector gets too hot, the data acquired is corrupted. With 3000 detectors it is not uncommon for detectors to malfunction, and it is imperative that all data from failed detectors be recognized before the map is generated.
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