Many different galaxies

The Giant Arc is the line of galaxies roughly in the centre of this image

ALEXIA M. LOPEZ/Jeremiah Horrock

An arc of galaxies that spans 3.3 billion light years – about 3.5 per cent of the observable universe – presents a big problem for one of the core tenets of cosmology.

Dubbed the Giant Arc by Alexia Lopez of the University of Central Lancashire, UK, who discovered the structure, it isn’t actually visible in the night sky – if it were, it would be as long as 20 full moons side by side.

Instead, Lopez spotted the …