Radio array starts work

Giant low-frequency sensor system on track to probe the birth of the first stars. At the heart of the LOFAR telescope is a collection of tile-like and dipole antennas.

The Netherlands, one of the most densely populated countries in Europe, would seem to be an inauspicious place to detect radio whispers from the distant Universe. Mobile-phone towers, television transmissions, planes overhead and even the odd burst of noise from a windmill create a background din in the radio sky.

But the builders of LOFAR, the Low-Frequency Array of radio receivers centred around the tiny village of Exloo, say that they have found ways to ignore the noise. In doing so, Dutch astronomers at ASTRON, the Netherlands Institute for Radio Astronomy in Dwingeloo, are opening up a region of the electro­magnetic spectrum that should hold clues to one of the earliest phases of cosmic history, when the first stars formed — an era beyond the ken of even the biggest optical telescopes.

“Many of the radio astronomers said this couldn’t be done,” says Heino Falcke, an astronomer at Radboud University in Nijmegen and chairman of the International LOFAR Telescope Board, the five-nation foundation that governs the €150-million (US$192-million) project. Yet Falcke and his colleagues defied the doubters by presenting their first results on 9 January at a meeting of the American Astronomical Society in Austin, Texas. “The message today is: the basic things all work. We can do this,” he said.

Mapping the low-frequency sky requires an expansive telescope as well as the ability to tune out noise. When completed later this year, the array will contain 2,700 slender dipole antennas tuned to 30–80 megahertz, and 43,000 antennas embedded in flat tiles a few metres square that are sensitive to 120–240 megahertz. The antennas will be concentrated in 40 stations across the Netherlands; 8 other stations in the United Kingdom, France, Germany and Sweden give the array extra angular resolution for fine-scale imaging. The fibre-optic data network that links the LOFAR antennas will also support sensor webs for geoscience and agricultural monitoring.

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