NASA / ESA / The GOODS Team / M. Giavalisco (UMass., Amherst)

Space used to be surprisingly crowded. The observable universe contains a whopping two trillion galaxies, making it 10 times as packed as we previously thought.

Since the Hubble Space Telescope started observing the deep sky, we’ve used its images to estimate that the universe we can see contains around 100 billion galaxies. But now, a team of astronomers led by Christopher Conselice at the University of Nottingham has generated 3D images of deep space by combining images from telescopes around the world, including Hubble.

They were able to infer the existence of galaxies that are too faint and too far away to be observed by today’s telescopes, and found that when the universe was a few billion years old, there were far more galaxies in a given volume than there are today. This resulted in the ironic-sounding conclusion that for us, 90 per cent of the galaxies in the observable universe are currently unobservable.

Because galaxies grow by merging and combining their stars, the low number of galaxies in modern times means they must have collided more often than we expected.