Laser system transforms VLTI capabilities for southern sky interferometry

by Robert Schreiber
Berlin, Germany (SPX) Nov 11, 2025

The European Southern Observatory's Paranal site in Chile marked a milestone as four lasers, each launched from an eight-metre telescope, began operations to create artificial stars. These lasers power a new adaptive optics system for the Very Large Telescope Interferometer (VLTI), correcting atmospheric blur anywhere in the southern sky and enabling the VLTI to observe a much wider range of targets.

This upgrade is part of the GRAVITY+ project, led by the Max-Planck Institute for Extraterrestrial Physics (MPE). GRAVITY+, focused on enhancing the highly successful GRAVITY instrument, involved installing lasers at each previously unequipped Unit Telescope. The system creates bright 'fake' stars 90 km above Earth's surface, allowing VLTI to image exoplanets, observe distant stars and galaxies, and study faint objects near the Milky Way's supermassive black hole.

"The VLTI with GRAVITY has already enabled so many unpredicted discoveries, we are excited to see how GRAVITY+ will push the boundaries even further," said Frank Eisenhauer, Principal Investigator of GRAVITY+ at MPE.

The upgrade includes advanced adaptive optics using state-of-the-art sensors and deformable mirrors. Prior to this, observing required pointing to nearby bright reference stars, constraining coverage. With the laser system, the VLTI is no longer restricted by reference star position and can conduct deep observations across the southern sky.

Taro Shimizu from MPE noted, "This opens up the instrument to observations of objects in the early distant Universe, such as the quasar we observed on the second night where we resolved the hot, oxygen emitting gas very close to the black hole."

Test observations targeted a cluster of massive stars in the Tarantula Nebula, revealing that a previously identified single massive star is in fact a close binary pair. This result highlights the enhanced sensitivity of the upgraded VLTI - now up to ten times greater - allowing astronomers to study faint and remote objects such as isolated stellar black holes and free-floating planets.

Julien Woillez, VLTI Systems Engineer, explained, "A big goal of GRAVITY+ is to allow for deep observations of faint targets." The improved facility will facilitate measurements of supermassive black holes and young planetary systems.

The laser adaptive optics concept at Paranal was envisioned as early as 1986 in the final report for the Very Large Telescope Project. It has now been realized, marking a transformative step for optical astronomy.

The GRAVITY+ consortium includes leading research institutions from Germany, France, Portugal, the UK, Belgium, Ireland, Mexico, and ESO.