Project to make ground-based telescopes ‘three times sharper than Hubble’

An Australian-led design project will develop a system that promises to revolutionise ground-based optical astronomy. Ben Lewis reports.

High atop a Chilean mountain, part of the European Southern Observatory.

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Astronomers are set to get a wider, sharper and more sensitive view of the universe than ever before thanks to an Australian-led project to upgrade one of the world’s most powerful ground-based telescopes.

The project, called MAVIS, will design a $32-million adaptive optics system to be installed on one of the eight-metre telescopes which make up the European Southern Observatory’s Very Large Telescope in Chile.

The Australian Astronomical Optics (AAO) consortium – made up of the Australian National University (ANU) and Sydney’s Macquarie University – will spend the next 15 months leading an international group to design adaptive optics which overcome atmospheric turbulence, which creates distorted and blurry images through optical telescopes.

While the turbulence delights people on the ground, causing stars to twinkle, it causes frustration for astronomers, with details lost in the mess.

Clearing up the problem has the potential to revolutionise ground-based optical astronomy, say researchers, with MAVIS eventually producing images up to three times sharper than the Hubble Space Telescope.

"Atmospheric turbulence really limits what we can see through a ground-based telescope,” explains Francois Rigaut from ANU.

“It's a bit like the phenomenon of objects appearing blurry on the horizon during a hot day. MAVIS will remove this blurring and deliver images essentially as crisp as if the telescope were in space, helping us to peer back into the universe in its infancy.”

An adaptive-optics system is made of three parts: a deformable mirror, which corrects the deformed light wave going through the atmosphere; a wavefront sensor, which uses a high-speed camera to sense the distortion of light; and a real-time computer, which calculates the corrections.

The initial designs for MAVIS involve a complex arrangement of three deformable mirrors, eight wavefront sensors and five laser guide stars. The technique, called Multi-Conjugate Adaptive Optics, points the wavefront sensors at different areas of the field of view, with the multiple deformable mirrors optically conjugated on different altitudes in the atmosphere.

The set-up provides accurate information on the atmospheric turbulence at different altitudes in the atmosphere, which is combined to achieve the best correction with the deformable mirrors. As the wavefront sensors look at different directions in the field of view, the correction can then also be optimised across it. In the case of MAVIS, the system will produce sharp images over a field of view 20 times larger than other adaptive-optics systems.

“The novelty of MAVIS is that it will deliver its corrected images in the optical range, combined with the extended field of view - this makes it a world first,” says Rigaut.

The upgraded telescope is expected to be completed by 2025.

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