智利高原上的宇宙之耳，聆听行星诞生的冷光
At 5,000 metres above sea level on the Chajnantor Plateau, the air is so thin and dry that unprotected skin cracks within minutes and unshielded electronics risk frying from unfiltered ultraviolet light. This hostile expanse in Chile’s Atacama Desert, one of the most arid places on Earth, is precisely what makes it the ideal location for the Atacama Large Millimeter/submillimeter Array, or ALMA. The telescope’s 66 high-precision antennas, most weighing around 100 tonnes, do not gather ordinary starlight; they capture radiation with wavelengths roughly a thousand times longer than visible light. In doing so, they open a window onto the cold, dark regions of the cosmos where new stars and planets are born, hidden behind thick veils of interstellar dust that block traditional optical telescopes.
ALMA is a feat of international cooperation, jointly funded by organisations from Europe, North America and East Asia, and operated as a single observatory. Its antennas can be repositioned across the desert floor, allowing the array to function much like a zoom lens. When spread up to 16 kilometres apart, they achieve an angular resolution sharper than that of the Hubble Space Telescope, enabling astronomers to discern structures as small as a few astronomical units in nearby stellar nurseries. The signals from all dishes are combined using a technique called interferometry, which demands timing precision down to a fraction of a trillionth of a second. This immense computing challenge is met by a dedicated supercomputer, the ALMA Correlator, which processes up to 17 quadrillion operations per second to synthesise a single coherent image.
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