The ESO’S AOF

The solution to imaging stars through a turbulent atmosphere

The European Southern Observatory’s Adaptive Optics Facility (AOF) is an innovative solution to overcome some of the barriers of ground-based astronomy.

The Earth’s atmosphere is a major obstacle for astronomers using ground-based telescopes, as the light from distant stars and galaxies becomes distorted as it travels through the turbulent air, creating indistinct snapshots. This causes inaccuracies in the data retrieved from the images, so stars close together may blur and appear as one. This is where the AOF comes in: it has been engineered to fix this effect in realtime to provide much sharper images and allow scientists to see more subtle details in astronomical objects.

The machine includes four 22-watt lasers that create artificial stars in the upper atmosphere by stimulating sodium atoms there. The adaptive optics module on the ground then uses these artificial stars as a guide to map the turbulence in the atmosphere and sends calculated correction data taken a thousand times per second to the thin, deformable secondary mirror. This mirror can constantly and rapidly change its shape to correct the light that is received from a celestial object, compensating for the atmospheric disturbance.

Using this method astronomers have captured spectacular images of fainter stars with sharper details. It is hoped that the technology will be used to gain more insight into deep space, in particular the formation of galaxies.

The nebula NGC 6369 seen without using the AOF (left) and when the AOF is providing turbulent atmosphere correction (right). The images with AOF are much sharper, clearer, and more detailed

The lasers provide artificial ‘stars’ to use as a guide, to track and compensate for the movement of the atmosphere