Unexpected neighbours

How many vicuñas do you spot in this Picture of the Week?* Vicuñas — a relative of the llamas and the alpacas — roam the Chilean Andes. They feel at home here on the 5000-metre-high Chajnantor plateau, next to their neighbour, the Atacama Large Millimetre/submillimetre Array (ALMA), a state-of-the-art telescope in which ESO is a partner.

ALMA consists of 66 antennas, which can be picked up and moved by the giant dark-yellow transporter that also features in this image. The ALMA antennas are located here for a very good reason: the extremely dry conditions at the Chajnantor plateau, deep in the Atacama Desert, are perfectly suited for observing some of the coldest objects in the Universe.

In contrast to stars, which are hot, bright and easy to see, these colder objects –– like the clouds out of which stars form –– are often faint in visible light. ALMA observes them at wavelengths of around a millimetre, thousands of times longer than what our eyes can see, because at those wavelengths these objects glow. Their signals, however, are heavily absorbed by the water vapour in the Earth's atmosphere so a high and dry site is ideal for a telescope like ALMA. For human beings, however, this can be a challenging environment to work in. The vicuñas, on the other hand, don’t seem very bothered, neither by the high and dry conditions nor by their giant antenna neighbours….…

*The correct answer is: eight vicuñas.