Solving Cosmic Cold Cases

From ESO, spectacular star-filled nights frame the telescope array of the new ALMA project, where scientists are taking on the mysteries of the cold hidden reaches of the universe. ALMA is the world’s largest astronomical project. But it is not a conventional telescope. Instead of collecting and analyzing visible light it looks in a different and largely unmapped part of the spectrum. By opening a new window on the cosmos, ALMA explores one of the last frontiers of astronomy — the cold and distant Universe. All in search of answers to some of the deepest questions about our cosmic origins. How do stars and planets form? How did the first galaxies form?

Sixty-six state-of-the-art antennas observe the Universe at millimeter and submillimeter wavelengths — one thousand times longer than visible wavelengths. This light reaches us from some of the coldest and most distant objects in the Universe. Water vapor in the atmosphere blocks these faint whispers from the hidden Universe, so to collect them we have to go to an extremely high and dry site — like Chajnantor.

The 66 antennas on the high plateau are a critical part of ALMA. Their big dishes collect the faint millimeter waves from space. These antennas are truly the state-of-the-art. Their surfaces are accurate to much less than the thickness of a sheet of paper. They can move precisely enough to pick out a golf ball at a distance of 15 kilometers.

In a truly global endeavor, the antenna components were constructed in several locations around the world, sent to Chile to be assembled. Detectors in each antenna register the finest nuances of the faint signals collected by the dishes. These detectors are the most sensitive of their kind and are cooled using helium gas to just four degrees above absolute zero.

Millimeter and submillimeter wavelengths give astronomers a unique window on the Universe. But to see them with the sharpness astronomers need, a single-dish telescope would have to be kilometers across (and impossible to build)! Instead, ALMA uses 66 separate antennas which can be spread out over the plain with separations of up to 16 kilometers. The antennas are linked and their signals combined. The result: one giant telescope as wide as the whole array, observing with unprecedented sensitivity and resolution.

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