(Sub)millimetre Stargazers

The bright sky above Chile’s Chajnantor plateau is sliced in two by the vast, vibrant ripple of the Milky Way. Here in the southern hemisphere, the magnificently rich centre of our galaxy is often directly overhead, its brilliant cloudy length stretching from horizon to horizon. Beneath its glow, a cluster of white antennas peers keenly up at the sky, illuminated by a bright yellow light that indicates to technicians whether or not it is safe to approach.

These telescopes are part of the Atacama Large Millimeter/submillimeter Array (ALMA), a giant interferometer made up of 66 individual antennas. These antennas work together over distances of up to 16 kilometres to study the Universe in remarkable detail. ALMA is designed to “see” light invisible to the human eye — at wavelengths of around a millimetre, between infrared light and radio waves. Such light comes from the coldest and most distant places in the Universe — such as vast clouds of gas and dust in interstellar space, and the most ancient galaxies — allowing ALMA to explore how stars and planets form and evolve.

Although these wavelengths can reveal never-before-seen objects and processes, (sub)millimetre astronomy has its difficulties. This light is heavily absorbed by water vapour in the Earth’s atmosphere, and thus struggles to reach the ground. In order to do this kind of astronomy, telescopes must be built on very high, dry sites; the Chajnantor plateau, located at an altitude of over 5000 metres in the Chilean Andes, is therefore an ideal location for ALMA.