In the mid-'90s, thanks to the Hubble telescope, humanity got its first look into the ancient universe and found it to be brimming with galaxies.

Using Hubble Deep Field images, astronomers predicted the observable universe — that which is observable from Earth — contains between 100 billion to 200 billion galaxies.

Turns out they may have been off — way off.

A team of international researchers now says the universe likely contains 10 times as many galaxies as previously believed — and the vast majority are too faint and far for us to see.

This Hubble image shows a portion of the the galaxies visible in the Great Observatories Origins Deep Survey, a large galaxy census conducted by several observatories to trace the formation and evolution of galaxies. (NASA, ESA/Hubble)

"It boggles the mind that over 90 per cent of the galaxies in the universe have yet to be studied. Who knows what interesting properties we will find when we observe these galaxies with the next generation of telescopes," lead author Christopher Conselice, an astrophysicist from the U.K.'s University of Nottingham, said in a European Space Agency release.

The scientists based their updated galaxy count on deep-space surveys by the Hubble Space Telescope and ground observatories, which they turned into 3D images and studied using new mathematical models.

Merging galaxies

According to Conselice and his colleagues, the universe has evolved dramatically over billions and billions of years.

The team looked more than 13 billion years into the past and found that galaxies are not evenly distributed throughout the universe's history. In fact, there were many more galaxies when the universe was just a few billion years old than there are today, and most of them were much smaller.

"This gives us a verification of the so-called top-down formation of structure in the universe," Conselice said, referring to the idea that over time, galaxies have merged together.

Why is the night sky dark?

The theory also adds weight to Olbers' paradox, named for astronomer Heinrich Wilhelm Olbers, who rejected the idea that the universe is infinite and static.

In an unchanging world with an infinite number of stars, he argued, there would be no such thing as the night sky because, as the Earth rotates, it would always be facing the light from one.

Therefore, the universe must be finite and dynamic, as astronomers now believe.

Teenagers look out at the night skyline of Mongolia's capital Ulan Bator on June 27, 2013. If the universe was infinite and unchanging, there would be no such thing as a night sky, according to Olbers' paradox. (Carlos Barria/Reuters)

"The team came to the conclusion that there is such an abundance of galaxies that, in principle, every point in the sky contains part of a galaxy," the ESA explains.

"However, most of these galaxies are invisible to the human eye and even to modern telescopes, owing to a combination of factors: redshifting of light, the universe's dynamic nature and the absorption of light by intergalactic dust and gas, all combine to ensure that the night sky remains mostly dark."