The James Webb space telescope has discovered the oldest black hole ever detected, which was thriving so soon after the Big Bang that it challenges our understanding of how these celestial behemoths form, astronomers said Wednesday.

The black hole was vigorously gobbling up its host galaxy just 430 million years after the birth of the universe during a period called the cosmic dawn, according to a study in the journal Nature.

That makes it 200 million years older than any other massive black hole ever observed, study co-author and Cambridge University astronomer Jan Scholtz told AFP. Yet it has a mass 1.6 million times greater than our Sun.

Exactly how it had time to grow that big so quickly after the Big Bang 13.8 billion years ago will provide new information "for the next generation of theoretical models" aiming to explain what creates black holes, Scholtz said.

Like all black holes, it is invisible and can only be detected by the vast explosions of light created when it gobbles up whatever matter is unlucky enough to be nearby.

It was this light that allowed the Hubble space telescope in 2016 to spot its host galaxy GN-z11, which is in the direction of the Ursa Major constellation.

At the time GN-z11 was the oldest -- and therefore most distant -- galaxy ever observed.