Point a space telescope at a seemingly empty patch of sky, collect light for days, and the darkness resolves into thousands of galaxies. A deep field is the closest thing astronomy has to a time machine.

Because light travels at a finite speed, the faintest, reddest smudges in these images show galaxies as they were within a few hundred million years of the Big Bang.

Surprisingly mature galaxies

Infrared deep fields have revealed galaxies in the early universe that appear brighter and more structured than many models predicted, forcing theorists to revisit how quickly the first stars and black holes assembled.

Why it matters

Deep fields anchor our entire cosmic timeline: star-formation history, the growth of supermassive black holes, and the reionisation of the universe are all calibrated against them. Each new, deeper image is another page of the universe's photo album — read backwards.