TORONTO -- Astronomers in Australia say they've made a discovery that calls into question our belief in how our galaxy was formed.
As , the creation of galaxies is believed to involve small clouds of stars and careening through space and occasionally colliding with each other, slowly growing until they reach galactic size.
However, scientists have long contended that when the Milky Way was formed somewhere around 12 billion years ago, it wasn't because of this gradual process, but because of two galaxies slamming together.
This theory posits that one of the two galaxies was much larger than the other, which could explain why the Milky Way's shape includes both a thick disk of older stars and a thin disk of newer ones.
It's an unusual origin story for an unusually shaped galaxy, the thinking goes, perhaps befitting what we see as our unique status in the universe.
The out of Australia, though, suggests a flaw in that reasoning. Scanning the cosmos with the Very Large Telescope in Chile, the astronomers say they found evidence that a nearby galaxy known as UGC 10738 has thick and thin disks of its own 鈥� which they say casts doubt on the notion that our galaxy formed in any special way.
"It was thought that the Milky Way鈥檚 thin and thick discs formed after a rare violent merger, and so probably wouldn鈥檛 be found in other spiral galaxies," Nicholas Scott, a postdoctoral research fellow in astronomy at the University of Sydney, said in .
"Our research shows that鈥檚 probably wrong, and it evolved 'naturally' without catastrophic interventions. This means Milky Way-type galaxies are probably very common."
UGC 10738's two disks mirror the Milky Way's when it comes to the age of the stars they contain, and also their contents. In both galaxies, the stars in the thin disk contain more iron, while their thick-disk counterparts are heavier on the likes of carbon, oxygen and silicon.
The astronomers say it is exciting to learn that our galaxy may be more normal than previously believed, because it will make it easier to learn about other galaxies by studying our own and the two billion stars it contains.
The distance between galaxies 鈥� UGC 10738 is located approximately 320 million light-years away from Earth, and it's one of our closer neighbours 鈥� creates significant obstacles for scientists. Even the Andromeda galaxy, which is next door to the Milky Way and likely beginning its own collision with it, is millions of light-years away.
Additionally, they say, finding other galaxies that are similar to ours increases the chances that they could contain potentially habitable planets.
The study was published Monday in The Astrophysical Journal Letters.
