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“Viewing” Radio Waves in Colour By Ross Tester from billions of years ago Imagine if you were able to “see” radio waves as they traversed the huge distances of space. A research team is using a new array in the Western Australian desert to not only view radio waves but assign them colours. T o most people in radio and electronics, frequencies above 50MHz are regarded as very high; indeed, by definition the VHF spectrum starts at 30MHz, with the Ultra High Frequency bands starting at 300MHz. To astro-physicists, 50-350MHz are regarded as low frequencies but are an increasingly important spectrum 26 Silicon Chip with a large amount of research into this band being done at installations around the world. By capturing the unbelievably feint radio signals emitted by stars and other celestial bodies at the far reaches of our (Milky Way) galaxy and beyond, they’re looking for clues into how those bodies began – countless millions (or billions) of years ago – long before our Earth had evolved. Here in Australia, the focus of such research is the Murchison Widefield Array or MWA, (a tiny section of which is shown above). This $50 million radio telescope is located at a remote site northeast of Geraldton, Western Australia. The MWA observes low-frequency radio waves (between 70 and 320 MHz) siliconchip.com.au and was the first of the three Square Kilometre Array (SKA) precursors to be completed. A consortium of 13 partner institutions from four countries (Australia, USA, India and New Zealand) has financed the development, construction, commissioning and operations of the facility. Since commencing operations in mid 2013 the consortium has grown to include new partners from Canada and Japan. Key science for the MWA ranges from the search for red-shifted HI (neural hydrogen) signals from the Epoch of Reionisation to wide-field searches for transient and variable objects (including pulsars and fast radio bursts), wide-field galactic and extra-galactic surveys, plus solar and heliospheric science. Colour views The research is being led by Dr Natasha Hurley-Walker, of Curtin University (Perth) and the International Centre for Radio Astronomy Research (ICRAR). What makes Dr Hurley-Walker and her team’s research of interest to much more than the radio astronomy community is their cataloging of 300,000 galaxies in glorious living colour – in other words, what the human eye would “see” if it could indeed view radio waves. It’s given the moniker of “GLEAM” – GaLactic and Extra-galactic Allsky MWA. In other words, the Murchison radio telescope is not simply looking into the far-flung reaches of our own Milky Way galaxy, it’s looking far beyond, to the limit of currently available technology. Normally a radio wave would just be noted as that – a radio wave, with a certain frequency and perhaps some unusual characteristics. “The human eye sees by comparing brightness in three different primary colours – red, green and blue,” Dr Hurley-Walker said. “GLEAM does rather better than that, viewing the sky in 20 primary colours.” “That’s much better than we humans can manage and it even beats the very best in the animal kingdom, the mantis shrimp, which can see 12 different primary colours,” she said. GLEAM is a large-scale, high-resolution survey of the radio sky, obsiliconchip.com.au serving radio waves that have been travelling through space – some for billions of years. The more distant the source of the radio waves, the longer they have taken to get to Earth and be detected “Our team is using this survey to find out what happens when clusters of galaxies collide,” Dr HurleyWalker said. “We’re also able to see the remnants of explosions from the most ancient stars in our galaxy, and find the first and last gasps of supermassive black holes.” GLEAM is one of the biggest radio surveys of the sky ever assembled, with an enormous area of the sky being scanned. Large sky surveys like this are extremely valuable to scientists and they’re used across many areas of astrophysics, often in ways the original researchers could never have imagined. Completing the GLEAM survey with the MWA is a big step on the path to SKA-low, the low frequency part of the international Square Kilometre Array (SKA) radio telescope to be built in Australia in the coming years. The SKA The Square Kilometre Array project is an international effort to build the world’s largest radio telescope, led by SKA Organisation based at the Jodrell Bank Observatory in England. Co-located primarily in South Africa and Western Australia, the SKA will be a collection of hundreds of thousands of radio antennas with a combined collecting area equivalent to approximately one million square metres, or one square kilometre. The SKA will conduct transformational science to improve our understanding of the Universe and the laws of fundamental physics, monitoring the sky in unprecedented detail and mapping it hundreds of times faster than any current facility. (SILICON CHIP featured the SKA project in the December 2011 issue and again in the July 2012 issue). Acknowlegement: Much of the information in this feature came courtesy of Dr Natasha Hurley-Walker and the GLEAM team. (See www. icrar.org/gleam). Ever wondered what radio waves from space would look like if you could see them? Try the applet http://gleamoscope.icrar.org/ These views are of the same section of sky, through the Milky Way galaxy and beyond. SC January 2017 27