What would the sky look like if we could see beyond the visible spectrum and gaze on the night sky in radio waves?
Ponder this no longer.
Australian astronomers working with international colleagues through the International Centre for Radio Astronomy Research in Western Australia have carried out one of the largest galaxy surveys across 20 radio frequencies, from 70 to 230 megahertz.
The lead researcher of the study of 300,000 galaxies, Natasha Hurley-Walker, said this is like looking at the sky in 20 primary colours.
"If we were honey bees we could see this in four primary colours; the mantis shrimp can see in 12 colours," Dr Hurley-Walker said.
"[In our imaging] we took the 20 radio frequencies and reduced them to three for the human eye to see," she said.
Each dot in the image is a radio galaxy and each of these is a collection of billions of stars with a supermassive black hole at the centre ejecting plasma jets at close to the speed of light and radio waves at light speed.
The research team at ICRAR has built what they call a "GLEAM-o-scope" to scroll through the survey data in different wavelengths.
Dr Hurley-Walker and her colleagues, including Curtin University's Randall Wayth, used the Murchison Wide Field array radio telescope in the Western Australian Outback for the survey.
The results of the Galactic and Extragalactic All-Sky MWA survey, or GLEAM, are published on Thursday in the Monthly Notices of the Royal Astronomical Society.
"Our team is using this survey to find out what happens when clusters of galaxies collide," Dr Hurley-Walker 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."
Associate Professor Wayth said GLEAM is one of the biggest radio surveys of the sky ever undertaken.
Dr Hurley-Walker said: "It's enormous. For a radio astronomy survey it's about as large as they get. We looked at 30,000 square degrees of sky." That's about three-quarters of the entire heavens.
As large as this is, it captures just a small number of the estimated two trillion galaxies in the universe.
The GLEAM view of the centre of the Milky Way, in radio colour. Red indicates the lowest frequencies, green indicates the middle frequencies and blue the highest frequencies. Photo: Curtin/ICRAR
The survey is an important step towards development of the international Square Kilometre Array that will be built in Australia and South Africa in coming years. It will be the biggest radio telescope in the world and will be partly based at the Murchison site.
Associate Professor Wayth said: "The survey gives us a glimpse of the universe that SKA will be probing once it's built. By mapping the sky in this way we can help fine-tune the design for the SKA and prepare for even deeper observations into the distant universe."
But why bother looking so far away?
"First of all it's simply fascinating," Dr Hurley-Walker said. "Our universe is so vast, why constrain ourselves to Earth?
"Gazing on the vastness of the universe reminds us how small we are," she said.
As well as these philosophical concerns, Dr Hurley-Walker said there are very practical reasons for this sort of radio astronomy.
"It's well-known that CSIRO radio astronomers developed protocols now used widely in Wi-Fi," she said. "But all the work we do helps develop new technologies, algorithms, receivers and supercomputers with broad practical application."
Dr Hurley-Walker has developed an Android mobile phone application to view her work and associated "Gleam-o-scope". Search "Gleam" on the Android store.
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