THE dreaded middle age spread is far more common than we think - even galaxies aren't immune.
Australian National University and University of Sydney researchers have discovered galaxies grow rounder and puffier as they age.
But the change in shape isn't from eating too many Milky Ways.
Co-researcher Matthew Colless from ANU said that stars in a young galaxy moved in an orderly way around the galaxy's disk, much like cars around a racetrack.
"All galaxies look like squashed spheres, but as they grow older they become puffier with stars going around in all directions," Professor Colless said.
"Our Milky Way is more than 13 billion years old, so it is not young any more, but the galaxy still has both a central bulge of old stars and spiral arms of young stars."
Researchers measured the movement of stars with an instrument called SAMI on the Anglo-Australian telescope at the Siding Spring Observatory in NSW.
They studied 843 galaxies within a hundred-fold range mass.
The team was surprised by the findings as the connection between galaxy shape and age wasn't previously obvious.
As a galaxy ages, internal changes take place and the galaxy may collide with others," said lead author Jesse van de Sande, from The University of Sydney.
"These events disorder the stars' movements."
Nature Astronomy published the results of the study.
