How do you create the world’s largest virtual optical telescope and the most advanced visible-light astronomical observatory? Teamwork. The Very Large Telescope at the Paranal Observatory combines the visual prowess of four huge telescopes — for the first time ever — to mimic a 130m wide mirror.
The Very Large Telescope is located 2365m above sea level in the windswept Atacama Desert of northern Chile. It’s been in service since to the European Southern Observatory (ESO) since 1999. It comprises four individual telescopes, each with an 8.2m wide parabolic mirror. They can operate individually or can be synced to become a coherent interferometric instrument, which provides a higher resolution than any of the four can produce themselves. When combined, the VLT becomes the biggest ground-based optical telescope on Earth.
The VLT Inferometer works like this. Light from outer space enters each of the four mirrors and is refracted through a series of underground tubes. As the light moves through here, a series of instruments correct any delay — essentially syncing all four feeds — before combining the image into a single beam of light. This hybrid beam is greater than what any individual telescope could achieve and offers nearly 20 times the zoom. “The more telescopes the better – you want to generate a plane to fill that virtual mirror, to increase the efficiency to reconstruct an image, in order to observe more complex objects in the sky,” Jean-Philippe Berger, a French astronomer involved in the project, told the BBC.
The primary drawback of this system, beyond its relatively small angular extent, is that as the light bounces through the underground tunnels, it dims — sometimes to as little as five per cent of what was initially captured. Even so, the new system should provide a clearer picture of otherwise unstudied celestial bodies. “With two telescopes, you typically observe round stars, for which you’re only interested in the diameter, or binary stars, where you can measure the separation between the two stars,” Berger said. “With four telescopes, you can start thinking about triple stars or young stars surrounded by a protoplanetary disc – a disc of dust and gas that forms planets.” I can’t wait to see the images this system will produce.