We know a lot about how the Milky Way formed, but there was always the worry that the Milky Way is not a typical spiral galaxy. "It you try to do it from overhead it's impossible, but it if you look from the side it's relatively easy."Ĭo-author Professor Ken Freeman from the Australian National University said, "This is an important step forward in understanding how disk galaxies assembled long ago. "It's a bit like telling apart short people from tall people," he said. Scott said UGC 10738's edge-on orientation meant it was simple to see which type of stars were in each disc. We're looking at some other galaxies to make sure, but that's pretty strong evidence that the two galaxies evolved in the same way."ĭr. "They were pretty much the same as those in the Milky Way- ancient stars in the thick disc, younger stars in the thin one. "Using an instrument called the multi-unit spectroscopic explorer, or MUSE, we were able to assess the metal ratios of the stars in its thick and thin discs," explained Dr. The galaxy is angled "edge on," so looking at it offered effectively a cross-section of its structure. Thick disc stars have three to 10 times less.)Īlthough such discs have been previously observed in other galaxies, it was impossible to tell whether they hosted the same type of star distribution-and therefore similar origins.Scott, van de Sande and colleagues solved this problem by using the European Southern Observatory's Very Large Telescope in Chile to observe UGC 10738, situated 320 million light years away. (The sun is a thin-disc star and comprises about 1.5% elements heavier than helium. Its thin disc stars are more recent and contain more metal. The research shows that UGC 10738, like the Milky Way, has a thick disc consisting mainly of ancient stars-identified by their low ratio of iron to hydrogen and helium. "It also means we can use existing very detailed observations of the Milky Way as tools to better analyze much more distant galaxies which, for obvious reasons, we can't see as well." This means Milky Way-type galaxies are probably very common. "Our research shows that's probably wrong, and it evolved 'naturally' without catastrophic interventions.
"It was thought that the Milky Way's thin and thick discs formed after a rare violent merger, and so probably wouldn't be found in other spiral galaxies," said Dr. This conclusion-published in The Astrophysical Journal Letters-has two profound implications. "From these results we think galaxies with the Milky Way's particular structures and properties could be described as the 'normal' ones." "Our observations indicate that the Milky Way's thin and thick discs didn't come about because of a gigantic mash-up, but a sort-of 'default' path of galaxy formation and evolution," said Dr.
The finding was made by a team led by Nicholas Scott and Jesse van de Sande, from Australia's ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) and the University of Sydney. It means that our spiral galaxy home isn't the product of a freak accident.
They appear to be the product of more peaceful change.Īnd that is a game-changer.
This suggests, contrary to previous theories, that such structures are not the result of a rare long-ago collision with a smaller galaxy. The galaxy, dubbed UGC 10738, turns out to have distinct 'thick' and 'thin' discs similar to those of the Milky Way.