ESO's Very Large Telescope fires lasers into the sky to create artificial stars

In a BBC report (September 2026) after a visit to ESO's Paranal observatory in Chile, Richard Fisher describes how the Very Large Telescope uses lasers to deal with the atmosphere, which, as ESO project scientist Amelia Bayo says, messes with the sharpness of starlight. The fix, adaptive optics, bounces the distorted light from the main mirror to a smaller mirror that deforms to match and cancel the distortion. Bayo says the idea is super simple, though the implementation is hard.

It needs a bright reference star. Where the sky has none, astronomers fire a laser: it excites a sodium-rich layer around 90km above the ground, the atoms emit photons the mirrors catch, and the artificial star can be placed anywhere ('a canvas where we can put the star anywhere we want', Bayo says). The idea traces to military satellite-tracking technology that astronomers realised could help ground observations.

After upgrades in 2016, one of the four 8.2-metre telescopes (Yepun) could fire four lasers at once to correct a wider field of view; each delivers 22 watts, about 4,000 times the maximum for a laser pointer, in a 30cm beam. The new lasers need no toxic liquid dyes or days of calibration: astronomers press a button and the beam stays put all night. By late 2025 ESO had installed the last of the new lasers, taking the total to seven, and all four main telescopes can now fire them, which BBC reports is a first. If a plane passes near the observed area, the lasers switch off automatically.

Natural stars bright enough to guide the correction are missing in many parts of the sky.

A sodium layer exists high in the atmosphere, giving the laser a reflecting surface wherever it points.

The deformable mirror can only correct what it can measure; the laser supplies the missing bright reference.

The newer lasers are stable and button-start, so night-shift astronomers do not need engineering support.

If the thing you need as a reference isn't where you need it, manufacture it: a laser can supply a reference point on demand.

In 2026 all four main VLT telescopes can fire lasers, so they can combine as a single virtual telescope with a wider field of view and capture details many times sharper than one alone. The BBC credits the VLT with the first image of an exoplanet and with tracking stars around the Milky Way's central black hole.