Filtering out Earth's radio noise
doi:10.1038/nindia.2013.8 Published online 23 January 2013
Using an array of sophisticated new radio telescopes, researchers claim that it is possible to filter out Earth-based radio noise and listen to radio signals from the early universe, largely filled with neutral hydrogen gas undergoing reionization around one billion years after the Big Bang1.
Studies have shown that radio waves from Earth's transmission networks make their way to the Moon and are reflected back to Earth. This journey prevents Earth-based radio telescopes from properly eavesdropping on radio signals originating from an epoch that witnessed the reionization of neutral hydrogen gas.
To overcome this drawback, the researchers have used the Murchison Widefield Array (MWA), a large array of low-frequency radio telescopes located in the radio-quiet Western Australia Outback. The MWA is a radically new type of radio telescope with no moving parts, and dependent on prodigious computing power to create exquisite, real-time, wide-field images of the radio sky.
The MWA listens to radio frequencies from 80 to 300 megahertz (MHz). Similar radio signals travel all the way from the epoch that saw the reionization of neutral hydrogen gas. The study found that the Moon might be useful as a calibration source for detecting radio signals from the epoch of reionization (EoR), offering a smooth and predictable thermal spectrum across the frequency band of interest.
Observing the Moon on two subsequent nights showed the properties expected for a cool, thermally emitting body, but the spectrum is corrupted by radio leakage from Earth, most notably within the frequency modulated radio band of 87.5 to 108 MHz.
The researchers say that these observations have implications for future low-frequency surveys and EoR detection experiments.