On a desert mountain in Chile, a mega telescope is peering over the event horizon of a black hole – the aim is to test Einstein's theories to the limit

The mountaintop of Cerro Paranal in the Atacama desert was blasted away to create a level site for the Very Large Telescope Enrico Sacchetti

ANTU, Kueyen, Melipal, Yepun. These four hulking figures dominate the summit of Cerro Paranal, a rust-red mountain in Chile’s Atacama Desert. Their home is among the most inhospitable places on Earth – a desolate, dusty terrain reminiscent of the surface of Mars.

As night falls, the giants slowly rotate and stir into life. Doors slide open, and within the structures vast mirrors begin to capture light from distant corners of the universe. Together they make up the world’s most powerful optical telescope: the Very Large Telescope.

You might have seen some of the VLT’s spectacular snapshots of swirling nebulae and far-away galaxies. But it was not built just to take pretty pictures. In the 20 years since the VLT saw first light, it has given researchers of the European Southern Observatory, a 17-nation astronomical collaboration, a clearer view of phenomena that could answer some of the universe’s greatest open questions, from how stars and planets form and whether there is life beyond our solar system, to how our underlying theories of the cosmos stand up. But enough is never enough: the giants are evolving, with the promise of even more spectacular discoveries to come.

This corner of Chile is an astronomer’s paradise. The sky is cloudless for 330 days of the year, there is almost no light pollution and the air contains barely any moisture that would otherwise block certain wavelengths of light. “When the moon is down, the night sky is absolutely amazing,” says staff astronomer …