Even galaxies experience mid-life crisis.

This was found out by a team of Australian astronomers whose research showed that Milky Way and Andromeda are in transition from being young and star-forming into old and stagnant galaxies.

The astronomers, led by Simon Mutch, of the Swinburne University of Technology in Melbourne, sought to determine the color the Milky Way and the nearby spiral Andromeda galaxy. And they found out that instead of the typical blue or red color which are signs of young, active galaxies, Milky Way and Andromeda are in a state of green.

"Green galaxies are commonly thought to represent galaxies which are undergoing the transition from being young, dynamic, energetic, star-forming blue galaxies to being old, lethargic red galaxies," Mutch told SPACE.com.

The astronomer added that the two galaxies will likely be unable to produce an active galactic nucleus or AGN, which is among the brightest radio signals in the universe and can be seen across great distances.

"Our finding that both the Milky Way and Andromeda are green suggests that there will be little cold gas left in both these galaxies when they merge sometime in the next 5 billion years or so," Mutch said.

The new color "provides us with an interesting open question as to what exactly is causing the Milky Way and Andromeda to be running out of fuel for producing new stars," he added.

The study was published in the Astrophysical Journal (July edition).