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The Milky Way's S Shape: A Strange and Fascinating Wobble

We usually contemplate the enormity of our galaxy, which spans roughly 100,000 light-years in diametre. However, our galaxy is so thin that if you were to travel at the speed of light directly upwards, you would exit the galaxy in merely 1,000 years.


How did our galaxy get so thin?

When we put it simply, galaxies are flat because of rotation, but it’s actually a lot more complicated than that. Just as everything else in our universe, the shape, and movement of these galaxies are affected by gravity and it’s this force that makes some galaxies appear so thin. It’s important to note that not all galaxies are flat. The most common type of galaxies to appear flat are spiral galaxies. Elliptical, lenticular, and irregular galaxies can have any number of different shapes.


illustration depicting the milky way galaxy bent out of shape due to millions of years of collisions

But, surprisingly, textbook depictions of our galaxy are wrong! Observations of our own galaxy, show that the Milky Way isn't in the category of those perfectly flat galaxies after all because our galaxy is not flat. Wait, what? This illustration here shows that the Milky Way is an S shape! If any alien civilisations are out there, they would see our galaxy like this and it would stick out like a sore thumb due to the odd shape amongst other spiral galaxies. The Milky Way is wobbling as a pizza crust is tossed into the air before baking. The further from the centre of the galaxy, the more distortion there is from the galactic plane.


How did our galaxy become so distorted?

The answer is very strange and fascinating. There are other galaxies inside the Milky Way. In fact, since our galaxy is very old, 13.4 billion years old, it has gone through galaxy collisions throughout its long life. It's so crazy old that it came into existence when the universe was just four hundred million years old, that is a blink of an eye cosmologically speaking.


People often talk about the galaxy collisions of the future, such as the upcoming collision with Andromeda, but little is spoken about collisions in the past. Moreover, the Milky Way merged in a head-on collision with a massive dwarf galaxy containing about one-to-ten billion solar masses in size, and this collision could produce the character changes in the stellar population currently observed in the Milky Way’s stellar halo. And due to these cataclysmic events, they are very difficult to hide, hence the S shape of the Milky Way. The damaging effects these encounters can cause to the Milky Way have, however, not been as well studied, and events even further in the past are even less obvious as they become blurred by the galaxy’s natural motions and evolution. It's believed, with observations, that it has collided with more than two galaxies.


Thank you for reading.

 

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