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Redefining the Milky Way: A Two-Armed Barred Spiral Galaxy

A photograph of the Milky Way rising above the horizon. Depositphotos.

The Milky Way, our very own galaxy, has been a subject of fascination for astronomers and stargazers alike for centuries. Now, a recent research suggests that our understanding concerning the shape of our galaxy may be due for an update. Scientists are now exploring the possibility that the Milky Way's true structure may differ from what we have previously believed.

Exploring the universe is something we love, and its not just because we are a curious species. The more we explore, the more we understand about our cosmic neighborhood. Regrettably, we don’t really know the exact shape of our galaxy, and this is because we can’t take a photograph of the Milky Way, since we are inside it. We can photograph other galaxies like Andromeda and see what they look like. However, when it comes down to the shape of our galaxy, whether it has two, three, or four arms, it all comes done to some guesswork and lots of science.

Nevertheless, astronomers have stepped forward in bettering our understanding of our galaxy. The Milky Way’s mesmerizing appearance as a hazy band of light in the night sky has long obscured its true structure. Astronomers have previously believed that our home galaxy is a four-armed spiral, but new research may soon change that understanding.

Unraveling the Milky Way’s True Form

Ye Xu and his team at the Purple Mountain Observatory in Nanjing, China, have used precise star measurements to create a more accurate map of the Milky Way. Their findings suggest that our galaxy is actually a two-armed barred spiral with minor arms branching from the more distant arms.

Classifying Galactic Shapes

Galaxies generally fall into elliptical blobs, irregular shapes, and spirals. Most spirals have two main arms, with the clearest examples being “grand-design” spirals. Minor arms often form as a result of collisions and mergers with other clusters and galaxies. Additionally, some spirals feature a central bulge or bar from which the spiral arms extend.

A Four-Armed Milky Way: An Unusual Phenomenon

If the Milky Way indeed has four arms, it would make it an exceptionally rare galaxy, warranting further investigation. Ye and his colleagues’ research is based on data gathered from new instruments that measure star distances with remarkable accuracy. These instruments include very long baseline interferometry and the Gaia space observatory.

Mapping the Stars

The team mapped the positions of over 200 masers (stars that emit microwaves), almost 24,000 O-B type stars, and nearly 1,000 open clusters of stars. After identifying the positions of these celestial objects, they searched for spiral shapes that fit their distribution. Ye and his colleagues ultimately concluded that the Milky Way is a barred spiral with two symmetrical inner arms: the Perseus and Norma Arms.

Multiple Arms and Unresolved Questions

The researchers suggest that the other arms are longer, more distant, and irregular, possibly resulting from galactic collisions in the past. These structures include the Centaurus, Sagittarius, Carina, Outer, and Local Arms. Consequently, Ye and his team classify the Milky Way as a multiple-arm galaxy, resembling most other multiple-arm galaxies in the universe.

Despite these groundbreaking findings, certain questions remain unanswered, such as whether the Norma and Perseus arms originate at the ends of the central bar. More data from Gaia and other observatories is needed to resolve these mysteries and provide a clearer picture of the Milky Way’s 3D structure.

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