Largest-ever adaptive telescope reveals unseen depths of space

After more than a decade of planning, the Very Large Telescope (VLT) in Chile has been upgraded with a new adaptive optics system.

Unit Telescope 4 at the European Space Observatory’s VLT can now capture much sharper views of space, including planetary nebulae and galaxies that were previously too faint to see.

The new Adaptive Optics Facility (AOF) makes thousands of calculations a second to compensate for atmospheric disturbances. It has been combined with the MUSE (Multi Unit Spectroscopic Explorer) instrument, an integral-field spectrograph that captures thousands of images of an object at the same time, each at a different wavelength of light.

“The AOF system is essentially equivalent to raising the Very Large Telescope about 900 metres higher in the air, above the most turbulent layer of atmosphere,” explains Robin Arsenault, AOF Project Manager. “In the past, if we wanted sharper images, we would have had to find a better site or use a space telescope — but now with the AOF, we can create much better conditions right where we are, for a fraction of the cost!”

Adaptive optics works to compensate for the blurring effect of the Earth’s atmosphere, using very thin deformable mirrors. These are combined with high-powered laser beams, shone into the sky to create ‘artificial stars,’ and provide a reference point for the correction.

“Adaptive optics systems aim at compensating the effects of Earth atmosphere on astronomical observations,” explained Algae Kellerer, a lecturer in astrophysics at the University of Cambridge to Professional Engineering. “Rapid variations in the optical index of air distort wavefronts and thereby degrade the angular resolution of telescopes. Adaptive optics systems correct for these wavefront distortions in real time.”

The new adaptive optics mirror is the largest ever produced at over a metre in diameter, and required cutting-edge technology to build. “As telescope sizes increase, the correction becomes ever more complex,” said Kellerer. “In 1989, the first astronomical prototype had 19 correction-elements, a 150Hz sampling-rate and it was using the light from one bright star as its signal. MUSE has several thousand correction-elements, sampling-rates above 1000Hz and it generates artificial stars using laser light!”