Aussie tech helps telescopes “see in the dark”

NGC 300

Australian technology will soon enable astronomers to get a clearer view of distant galaxies, by reducing the effect of the natural airglow of the sky.

AUSTRALIAN SCIENTISTS have made a major breakthrough in the drive to improve their view of the night sky and greatly increase the efficiency of ground-based telescopes.

While the night sky looks dark to the naked eye, to an astronomer working at infrared wavelengths the air actually glows brightly, drowning out the view of distant astronomical bodies.

This happens because molecules in our atmosphere emit their own infrared radiation, swamping the faint infrared light coming in from deep space.

What astronomers have needed is a way to filter out the atmospheric emission while letting through the infrared waves from stars and galaxies.

Traditional filters can only remove selected wavelengths at a time. What if a system could be devised that removes many at once?

Enter the “photonic lantern” and high-tech, wavelength-suppressing optical fibres, both the brainchild of Professor Joss Bland-Hawthorn (University of Sydney) and the team he leads.

The complex system, under development since 2004, recently underwent its first real test under the night sky—at Siding Spring Observatory in New South Wales—and passed with flying colours.

The system removed the unwanted air emissionwavelengths just as planned, while letting through the infrared from deep space. In effect, it made the sky look darker and clearer.

Joss Bland-Hawthorn

Professor Joss Bland-Hawthorn leads the team that has developed the photonic lantern and wavelength-suppressing optical fibres. Photo courtesy University of Sydney.

The results of the field test were published this week in the scientific journal, Nature Communications.

Looking deeper into space

The optical fibres are specially made with internal patterns that act to filter out the unwanted wavelengths, while the photonic lantern combines the output from multiple fibres. That output can then be fed into a spectrograph, a device that splits light into separate wavelengths and enables analysis to be made of the chemical nature of the stuff (stars, galaxies, nebulae) that emitted the original infrared light.

Infrared wavelengths are very important because visible wavelength light emitted from astronomical bodies when the universe was young, has by now been redshifted into the infrared by the expansion of the universe. So in order to study the universe’s past, astronomers need to see at infrared wavelengths.

The first operational device to use the new photonics was commissioned earlier this year on the Anglo-Australian Telescope. This prototype instrument, called GNOSIS, paves the way to a more powerful instrument now under development by the AAO and the University of Sydney. Called SUNESIS, it will be operational by the end of 2012.

“This will mean we’ve gone from project inception to completion within 12 months, a remarkable effort,” says Bland-Hawthorn.

And they’re also aiming to have the technology ready soon for use on other major telescopes throughout the world.

“In particular, we’re aiming at the current 8- to 10-metre class of telescopes—the largest in the world—and then the new generation of 30-metre telescopes that are currently in the design phase,” says Bland-Hawthorn.

When installed on such large telescopes, the system will enable astronomers to see five times deeper into space in the infrared part of the spectrum, which corresponds to a 100-fold increase in the volume of space covered. And that means thousands more targets for their telescopes.

And that’s not the end of it. Space-based applications also beckon, and the University of Sydney team aims to test out other uses of the photonics technology aboard a micro-satellite to be launched in 2012, as well as with high-altitude balloon flights in collaboration with NASA.

Story by Jonathan Nally. Galaxy image courtesy ESO.

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