How many galaxies are present in the universe? Two trillion, say astronomers

Our universe is home to as many as two trillion galaxies, a number which is ten times more than thought previously, a new study has revealed. 

Astronomers have long sought to find out the number of galaxies present in the observable universe, the part of the cosmos where light from distant objects has had time to reach us.

Images from the Hubble Space Telescope were used by the scientists over the last 20 years to estimate that the universe has around 100 to 200 billion galaxies.

Scientists are able to study just 10 per cent of these galaxies with the help of current technology. Once bigger and better telescopes are developed, the remaining 90 per cent will be seen, said researchers led by Christopher Conselice from University of Nottingham in the UK.

A PhD student at Nottingham named Aaron Wilkinson carried out the initial galaxy-counting analysis, which was crucial to establish the feasibility of the larger-scale study.

Pencil beam images of deep space from telescopes around the world, and especially from the Hubble telescope were then converted into 3D maps by Conselice's team.

With this, they were able to calculate the density of galaxies as well as the volume of one small region of space after another.

The team by conducting the research managed to establish how many galaxies were missed, much like an intergalactic archaeological dig, researchers said.

The results of the study are based on the measurements of the number of observed galaxies at different epochs - different instances in time - through the universe's history. 

Conselice and his team collaborated with scientists from Leiden University in the Netherlands and the University of Edinburgh. The team examined how many galaxies were there at a given epoch and they found that there were significantly more at earlier times.

It appears that when the universe was only a few billion years old there were ten times as many galaxies in a given volume of space as there are within a similar volume today.

Most of these galaxies were low mass systems with masses similar to those of the satellite galaxies surrounding the Milky Way.

"This is very surprising as we know that, over the 13.7 billion years of cosmic evolution since the Big Bang, galaxies have been growing through star formation and mergers with other galaxies," said Conselice.

"Finding more galaxies in the past implies that significant evolution must have occurred to reduce their number through extensive merging of systems," Conselice said.

"We are missing the vast majority of galaxies because they are very faint and far away. The number of galaxies in the universe is a fundamental question in astronomy, and it boggles the mind that over 90 per cent of the galaxies in the cosmos have yet to be studied," he added.

The research appears in The Astrophysical Journal. 

(With inputs from PTI)