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Image Astro du jour
Four laser beams shine across the magnificent Southern sky in today’s Picture of the Week. Glowing beads of light, one on each beam, are created by a thin layer of clouds crossing the path of the lasers and hint at the source of these beams. Emitted by the four Unit Telescopes (UTs) of ESO’s Very Large Telescope (VLT), here working together as part of the VLT Interferometer (VLTI), the shape of the four bright spots mirrors the layout of the UTs. But these spots were a happy accident caused by clouds that happened to be in the way — the lasers themselves target a much higher layer in our atmosphere.
As of November 2025, all four UTs are equipped with lasers, as part of a series of significant upgrades to the VLTI named GRAVITY+. Each laser creates an artificial “star”, 90 kilometres above the Earth’s surface, used to detect how the moving atmosphere distorts incoming light. This enables a telescope to make real-time corrections that cancel out the atmosphere’s blurring effect. “Unblurred” light from the four UTs can then be combined to make detailed observations of distant cosmic objects. This upgrade has unlocked the entire Southern sky to the VLTI by allowing the system to observe much fainter objects than before.
In this image the telescopes, and the lasers, are pointing to the centre of our galaxy, the region around the supermassive black hole Sagittarius A*. If you look closely at the apex of the laser triangle you may be able to discern the four tiny artificial stars created by the beams. Deeper observations at the heart of the Milky Way are a key science motivation for GRAVITY+, in particular to understand the properties of our supermassive black hole.
“For me, this image is an accomplishment,” says photographer and ESO astronomer Anthony Berdeu, who has worked on the GRAVITY+ project since 2022. “These were intense, challenging but fascinating years where I had the chance to work with great and talented people in the consortium and at ESO,” he reflects. After years of hard work implementing the upgrades, “the first night the lasers were shined to point at the galactic centre, I had to be on the VLT platform to take a picture.” His photograph captures not just the four lasers — appearing to pierce the dark patch where cosmic dust clouds mask the galactic centre — but also the bright band of the Milky Way to the lower right and the Lagoon and Trifid nebulae (both around 5000 light years away) to the left. Additionally, Berdeu got a “nice surprise” when passing thin clouds intercepted the lasers, producing an outline of the UTs in gold spots, “adding some drama to the scene.”
Links
Annotated version of this image with the telescope layout
Time-lapse video of the lasers passing through the clouds