A close-up of the antenna on the EDGES system, a custom-built radio spectrometer that was deployed at the Murchison Radio Astronomy Observatory in Western Australia. The four panels are made from aluminum sheet metal and supported by PVC legs. The white bag under the antenna encloses analog amplifiers and calibration circuits and was a last minute addition to help protect the system from occasional strong rainstorms during its three months of unattended operation. The metal screen visible on the ground under the antenna is called a ground screen and improves the sensitivity of the antenna toward the sky.
EDGES is a small-scale radio astronomy experiment designed to detect a never-before-seen signal from the early universe during a phase in its history called the Epoch of Reionization (EoR). The EoR phase is linked to many fundamental questions in cosmology. EDGES has a simple design that includes an antenna, an amplifier, some calibration circuits and a computer, all of which are connected to a solar-powered energy source.
EDGES was developed by Judd Bowman, an assistant professor at the School of Earth and Space Exploration in Arizona State University's College of Liberal Arts and Sciences, and Alan Rogers of the Massachusetts Institute of Technology. "Our goal is to detect a signal from the time of the Epoch of Reionization. We want to pin down when the first galaxies formed and then understand what types of stars existed in them and how they affected their environments," says Bowman.
Bowman and Rogers deployed EDGES at Murchison to measure the radio spectrum between 100 and 200 megahertz. Instead of looking for early galaxies themselves, the experiment looks for the hydrogen gas that existed between the galaxies.
"This gas would have emitted a radio line at a wavelength of 21 cm--stretched to about 2 meters by the time we see it today, which is about the size of a person," explains Bowman. "As galaxies formed, they would have ionized the primordial hydrogen around them and caused the radio line to disappear. Therefore, by constraining when the line was present or not present, we can learn indirectly about the first galaxies and how they evolved in the early universe."
Because the amount of stretching, or redshifting, of the 21 cm line increases for earlier times in the universes history, the disappearance of the intergalactic hydrogen gas should produce a step-like feature in the radio spectrum that Bowman and Rogers measured with their experiment.
After careful analysis of their observations, the researchers were able to show that the gas between galaxies could not have been ionized extremely rapidly, marking the first time that radio observations have directly probed the properties of primordial gas during the EoR and paving the way for future studies. "Were breaking down barriers to open an entirely new window into the early universe," says Bowman. "Our goal, eventually, is to make radio maps of the sky showing how and when reionization occurred. Since we cant make those maps yet, we are starting with these simple experiments to begin to constrain the basic properties of the gas and how long it took for galaxies to change it," adds Bowman. "This will improve our understanding of the large-scale evolution of the universe."
A paper discussing this research, which was supported in part by a grant from the National Science Foundation (AST 09-05990), was published in the Dec. 9, 2010, issue of Nature. (Date of Image: September 2009 thru October 2010) [Image 3 of 4 related images. See Image 4.]