Largest Telescope Would Be Out of this World

By Jeremy Hsu
16 April 2008
A telescope on the far side of the moon could probe the "dark ages" of the universe while blocking out the radio-wavelength noise of Earth civilizations.

Up to one hundred thousand antennas would form the Dark Ages Lunar Interferometer (DALI), the largest telescope ever built, and allow astronomers to hear faint whispering signals from a time when no stars even existed.

"This will look at one of the most fundamental questions ever conceived, back when the universe was made up almost entirely of hydrogen and helium — no stars, no galaxies," said Kurt Weiler, senior astronomer at the U.S. Naval Research Laboratory.

The so-called dark ages of astronomy describe a half-billion year period following the Big Bang when clouds of ionized gas cooled as the universe expanded. The only faint noise came from hydrogen atoms doing spin-flips, which gives off radio-wavelength signals that astronomers can pick up on. Scientists currently estimate that the universe is about 13.7 billion years old.

"What happens is that because of the Big Bang there's a background glow," Weiler noted. "The spin-flip will absorb the glow of the older material and will give us a signature that we can see."

However, the ongoing expansion of the universe has stretched or red-shifted the hydrogen signature from just 21 centimeters to several meters. That means the signals can easily get masked by louder Earth transmissions in the same wavelength, unless astronomers find a quieter listening spot.

"The back side of the moon is the only place in the local universe shielded from manmade transmissions," Weiler told SPACE.com.

The DALI design resembles existing radio telescope arrays in the Netherlands, Australia, and New Mexico. But sending such an array to the moon requires lighter material that can save on launch costs, not to mention survive the harsh lunar conditions.

One candidate is polyimide, a plastic-like film which can act as an antenna when plated with metal. University of Colorado researchers are testing the film's durability by exposing it to harsh ultraviolet rays, as well as the extreme temperatures like that of boiling water and super-cold liquid nitrogen.

The film antennas would be rolled up and then unrolled for deployment across 30 miles (48 km) of lunar surface, arrayed in one thousand stations containing one hundred antennas each. Still, getting the entire load to the moon represents a challenge.

"Even though each antenna may weigh a few ounces, you're talking about needing at least heavy lift vehicles," Weiler noted. "They all add up fast."

The U.S. Naval Research Laboratory is sharing NASA funding with an MIT-based team working on another lunar telescope separate from DALI. Their collaboration may finally realize a dream that many astronomers had even before the first Apollo landings on the moon.

"Probing the dark ages presents the opportunity to watch the young Universe evolve," said Joseph Lazio, NRL astronomer and head of the DALI proposal. "Just as current cosmological studies have both fascinated and surprised us, I anticipate that DALI will lead both to increased understanding of the Universe and unexpected discoveries."