The Truth About The 'Broken Arm' Of The Milky Way

The Milky Way, the galaxy Earth calls home, is incomprehensibly large: NASA states that it contains an estimated 100 billion stars. The solar system is on the outskirts, around 25,000 light-years away from the galaxy's center. The scale of space is truly vast.

Needless to say, the Milky Way harbors a great number of mysteries. Its curious "broken arm" is just one of these, and it is believed that it could tell us more about the galaxy's origins.

As Futurism explains, it is impossible to see the Milky Way itself, because the Earth is inside it. However, it is possible to determine what it looks like by comparing certain elements with other galaxies that are visible. Through this process, scientists have concluded that the Milky Way is a spiral-shaped galaxy, much like many others. In the arms of these spirals, then, lies the fascinating "break" that was discovered in August 2021.

As Space reports, the European Space Agency's Gaia mission and the Spitzer Space Telescope at NASA discovered this curious feature of the Milky Way's Sagittarius Arm. It is a stretch of gas clouds and stars that protrudes away from the rest of the arm for a distance of around 3,000 light-years. California Institute of Technology astrophysicist Michael Kuhn stated that one of the most important factors of spiral arms is "how tightly they wind around a galaxy," per Space. Kuhn went on to say that the pitch angle of the Sagittarius Arm, previously believed to be around a 12-degree angle, now appears to be close to 60 degrees (a true circle being a zero-degree angle).

Per Illumination (via Medium), this "break" cannot be deemed a true arm in and of itself, as it lacks the crucial characteristic of being attached to the nucleus (center) of the galaxy. Named Cattail, it's a significant discovery.

SciTechDaily reports that such structures, orientated very differently to the rest of the arm, are also found elsewhere in different galaxies. This discovery is the first sign that the Milky Way may have some as well, a question scientists have long wanted to answer. The (relatively) young stars of this "broken arm" appear to have all formed at around the same time and relatively close together. The new data could provide important clues about the age of the Milky Way, the structure of it, and the forces that act upon it.