Stars on demand: four lasers sharpen a black hole’s view

Four bright yellow streaks in this ESO image are artificial stars, not beams aimed at the galaxies to their right. Generated by lasers rising from the Very Large Telescope’s four Unit Telescopes in Chile, they give astronomers reference points for measuring the atmosphere’s distortion of starlight.

The beams encounter sodium atoms about 90 km above the ground, making them glow. That sodium occupies a layer roughly 5–10 km thick: photographed from 2.5 km away, its illuminated columns appear elongated, while from the telescopes sending up the beams they look like points.

Adaptive optics (technology that corrects atmospheric distortion) monitors these artificial stars and drives a thin, flexible mirror that changes shape hundreds of times per second. Those adjustments counteract the shifting blur, bringing the astronomical target into sharper focus.

A clearer view from beneath the atmosphere

The target here is the supermassive black hole at the centre of NGC 3227. Gas drawn towards the black hole powers its bright, active centre, which ESO astronomer James Leftley is studying with the GRAVITY and MATISSE instruments.

The VLT Interferometer (a system combining light from separate telescopes) links the four Unit Telescopes to work like a telescope up to 130 metres across. Lasers added through the GRAVITY+ upgrade extend atmospheric correction across almost the entire southern sky; these artificial stars are atmospheric beacons, not orbiting spacecraft.

Orbital Radar tracking data lists 16,659 active satellites in orbit as of 5 November 2026. Orbital Radar’s live catalogue contains 32,018 objects, including debris, as of 5 November 2026.

For readers turning from this distant galaxy to objects crossing their own sky, Orbital Radar’s Pass Predictor identifies visible satellite passes. The distinction matters: satellites travel around Earth, whereas these laser-created reference points glow within its atmosphere.