Just Like Humans, Galaxies Get Rounder As They Age

Getting rounder with age isn't just for humans. A middle-age spread, scientists have discovered, is more of a universal condition. Even galaxies, they've found, become more rotund with the passage of years.

Pancake-shaped young galaxies slowly thicken as they age, researchers report in a research paper published in the journal Nature Astronomy. Young galaxies are thin and orderly, but older galaxies are rounder and messier.

"All galaxies look like squashed spheres, but as they grow older they become puffier with stars going around in all directions," said Matthew Colless, director of the Australian National University Research School of Astronomy and Astrophysics and co-author on the research paper, in a statement.

4_24_Sombrero Galaxy
This image depicts the Sombrero Galaxy, an extremely thin, pancake-like galaxy. Hubble Heritage Team/NASA

The Milky Way, he added, sits somewhere between these flat and round extremes. Our galaxy has more than 13 billion years under its belt, but is looking pretty good for its age. Its flatter, spiral arms compensate for its central bulge of old stars.

Read more: Andromeda Galaxy Brought Down To Size for Head-to-Head Collision With Milky Way

The team tracked the movement of stars with a telescope to figure out the shape of 843 galaxies, big and small. Then, they used color to estimate the age of each galaxy. "Young, blue stars grow old and turn red," explained co-author Nicholas Scott from the University of Sydney in the statement. "When we plotted how ordered the galaxies were against how squashed they were, the relationship with age leapt out. Galaxies that have the same squashed spherical shape, have stars of the same age as well."

Astronomers have known for some time that age and shape were connected in extremely flat and extremely round galaxies. This is the first time, however, they've shown a link in galaxies of "all shapes, all ages [and] all masses," Scott explained.

4_24_M87 Galaxy
This image portrays galaxy M87. This elliptical galaxy is one of the oldest and roundest in the universe. E Baltz (Stanford University)/P Cote (Herzberg Institute of Astrophysics)/Hubble Heritage Team (STScI/AURA)/ESA/NASA

The connection between shape and age in less extreme galaxies surprised the team. But now, they think it could signal an important relationship. Neat, young galaxies can become more jumbled over their lifetime. "As a galaxy ages, internal changes take place and the galaxy may collide with others," lead author Jesse van de Sande from the University of Sydney explained in the statement. "These events disorder the stars' movements."

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Now, the team is hunting for more relationships like age and shape that can explain the enormous, complicated clockwork ticking away behind the myriad of galaxies in space. "To see those relationships, you need detailed information on large numbers of galaxies," co-author Julia Bryant from the University of Sydney added.