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GALACSI Adaptive Optics System Ready to be Mounted on the VLT

The VLT’s MUSE will soon be able to see even more clearly

15 april 2016

The GALACSI adaptive optics module, built by ESO’s engineers at its headquarters in Garching, Germany, has been thoroughly tested and has passed with flying colours. It will be shipped to Chile later this year to be fitted to ESO’s Very Large Telescope (VLT), on Cerro Paranal.

GALACSI is a part of the adaptive optics system which will significantly increase the performance of the MUSE instrument, a panoramic integral-field spectrograph working at visible wavelengths. The MUSE instrument and the GALACSI system together will be known as the MUSE facility. Adding GALACSI to MUSE will essentially double the amount of energy in each image pixel, providing astronomers with a much more powerful tool. As well as bringing about a huge improvement in the VLT’s capabilities, GALACSI and the other elements of the adaptive optics system are advancing technology that will be used on the forthcoming European Extremely Large Telescope.

Adaptive optics systems compensate for the effects of atmospheric turbulence, which degrades images obtained by ground-based telescopes. When it passes through the atmosphere, light from a celestial object gets jiggled around, meaning that the telescope sees a blurred image. GALACSI will rely on 4 sodium lasers launched from the centre piece of one of the Unit Telescopes of the VLT to produce “artificial stars”, known as guide stars. Sensors then follow the motion of these guide stars as the light from them flickers in the turbulent atmosphere. That allows a computer to calculate the correction that must be applied to the telescope’s deformable secondary mirror (itself a new addition to the VLT) to compensate for the atmospheric disturbance. In this way, extremely sharp images of the real celestial objects can be obtained.