The Precision Array to Probe the Epoch of Reionization, called “PAPER” for short, is a specialized, long-wavelength-gathering radio telescope. PAPER searches for signs of changing times in the early Universe, 500 million years after the Big Bang, when basic elements were blasted back into protons and neutrons by the energetic shining of the first stars and galaxies. This ancient hydrogen emission, traveling for billions of years in an expanding Universe, arrives in much longer wavelengths than it had when it radiated from the first stars. PAPER is built to detect those long wavelengths.
PAPER was developed by Rich Bradley and Don Backer in the early 2000s. They chose to build their first array in the Galford Meadow at the back end of the Green Bank Observatory property, near the 85-2 antenna where the Green Bank Interferometer's track ended. The long wavelengths collected by PAPER overlap with those of FM radio stations, so our radio-quiet Green Bank is a perfect location to host North America’s 32-telescope array.
Each antenna is a cross-shaped dipole made in the machine shops in Green Bank. Antenna signals are sent over a 75-ohm TV coaxial cable to the central correlator housed in a small shed near the array. In 2010, the first sky maps were produced by PAPER astronomers.
The Green Bank PAPER array is the smaller cousin to larger, 64-antenna arrays in Australia and South Africa.
PAPER is a partnership between NRAO staff scientists and scientists at University of California at Berkeley, the University of Virginia, the University of Pennsylvania, and SKA South Africa. It is a pathfinder for future arrays that hope to image the first light of the Universe. As a pathfinder, PAPER scientists report on antenna design, array configuration, data storage, digital signal processing, and calibration and RFI struggles.