More than 44,000 radio antennas will soon link over the Internet to create one of the most ambitious radio telescopes ever built. Its job will be to scan largely unexplored radio frequencies, hunting for the first stars and galaxies and, potentially, signals of extraterrestrial intelligence.

The array is designed to monitor low-frequency radio waves. One key source of these emissions are extraordinarily feeble signals from the cold hydrogen gas that dominated the cosmos during the so-called Dark Ages of the uni­verse. As stars eventually flared into being, they would have left scars on this hydro­gen, and by analyzing how the radio signals from this gas altered over time, sci­entists can learn much about how the first galaxies came to be.

The Low Frequency Array (LOFAR) will consist of banks of antennas in 48 stations in the Netherlands, Germany, France, Sweden and the U.K., all connected via fiber-optic cables. A supercomputer will combine signals from these stations, transforming the array into what may be the most complex and versatile radio telescope ever attempted, says Heino Falcke, chair of the board for the International LOFAR Telescope.

The array will be finished by the middle of this year and will have the capacity to sweep the entire northern sky in 45 days. All told, it will have a maximum resolution equivalent to a telescope 620 miles (1,000 kilometers) in diameter. In addition, the design is expandable, mean­ing that researchers can al­ways add stations later, says Michael Wise of ASTRON, the Netherlands Institute for Radio Astronomy.

In addition, LOFAR is very fast, capable of mea­suring events only five bil­lionths of a second long. Moreover, the fact that LOFAR is essentially many different radio telescopes knit together means it can run, say, three different science projects simulta­ne­ous­ly, Wise says.

In the next few years, the array will also scan for artificial radio emissions as part of the search for extraterrestrial intelligence (SETI) at lower, neglected frequencies than past SETI missions.

This article was published in print "Scanning for E.T.'s Calls."