Growing big with time is a condition synonymous to humans and animals, but a new study, coming from a group of Australian researchers, suggests even the galaxies sitting in our universe increase in size and get puffier as they age.

Young galaxies start as thin objects with well-behaved stars inside. These stellar bodies move around the disk of the galaxy in an orderly pattern much like cars around a racetrack. But as billions of years pass by, the galaxies start getting rounder.

"All galaxies look like squashed spheres, but as they grow older they become puffier with stars going around in all directions," study co-author Matthew Colless, Director of the ANU Research School of Astronomy and Astrophysics and Chief Investigator at the ARC Centre of Excellence for All-sky Astrophysics in 3D, said in a statement.

NGC 4660 in the Virgo cluster of galaxies_cropped_0
Galaxies get rounder and puffier with age. Pictured, NGC 4660, which lies among the Virgo cluster of galaxies, is an example of an old galaxy. ESA, NASA, and E.Peng (Peking University, Beijing)

Colless and colleagues posited this theory after studying more than 800 galaxies of different types and with varying levels of mass. They determined the shape of each and every galaxy by discerning the movement of the stars they hosted with the Anglo-Australian Telescope and its SAMI instrument.

Then, they used the distinction between the colors of those stars to estimate the age of each galaxy and define the relation between its shape and age. "Young, blue stars grow old and turn red," study co-author Nicholas Scott said in the same statement.

"When we plotted how ordered the galaxies were against how squashed they were, the relationship with age leapt out,” Scott added. “Galaxies that have the same squashed spherical shape, have stars of the same age as well."

The connection applies to all galaxies, no matter what shape, age or mass, and comes as a major surprise to the research team. This is because until now the group thought aging and shape was linked only to extreme galaxies or those being absolutely flat or round.

That said, the group believes the find could help them discover other simple yet powerful relationships that lie under the complexity seen in distant galaxies. "As a galaxy ages, internal changes take place and the galaxy may collide with others," lead author Jesse van de Sande said. This could be the reason behind messy stellar movements in older galaxies.

However, to uncover any such relation, they’ll need more data from a bigger chunk of galaxies, something the successor of the SAMI, dubbed Hector, is being developed to achieve. The instrument — set to work at the Australian Astronomical Observatory — will observe 100 galaxies at a time.

The study, titled “A relation between the characteristic stellar ages of galaxies and their intrinsic shapes,” was published April 23 in the journal Nature Astronomy.