Using data from the Spitzer Space Telescope and Gaia Observatory, researchers have discovered a “fracture” in one of the spiral arms of our galaxy, Milky Way. The curious formation is in the arm of Sagittarius, where, at a certain point, there are a large number of seemingly “out of place” young stars.
These stars move in the same direction and at roughly the same speed. At first glance, it’s easy to deduce that they are part of a bow arm, but the scientists’ conclusion is a little unusual: they may be the remains of a hitherto unknown arm that has broken off.
Spiral arms wrap around the cores of galaxies, and current models suggest that this twist can be measured with an angle of inclination compared to a perfect 0-degree circle. Using this approach, the bow arm would have an angle of inclination of about 12 degrees, while new observations show that the tilt angle of the ‘joking’ structure is about 60 degrees.
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The reason for this discrepancy remains unclear, but the study authors made some considerations about the different possibilities. In all, 25 regions of star formation have been identified arranged in this linear structure with a length of approximately 1 kpc (equivalent to 3,261.56 light-years). The structure includes huge areas of “incubation” of famous stars such as the M8, M16, M17 and M20.
Despite the odd angle of 56 degrees, “the movements in the structure are coherent, with speeds in the direction of the galaxy’s rotation (…) slightly above average, and slight inward deviations,” said the authors of the article. Published in Astronomy and Astrophysics. Astronomers still don’t fully understand the origin of the spiral arms of galaxies, but the new study may be helpful in solving this mystery.
In part, the paper’s usefulness to theoretical models is that the stars of the newly discovered structure formed at the same time and region, and were likely affected by changes in the Milky Way, such as gravitational forces and distortions associated with galactic rotations. “This structure is a small part of the Milky Way, but it can tell us something important about the galaxy as a whole,” said study co-author Robert Benjamin.
Finally, the authors leave the true nature of this structure open for further clarification – whether it is an isolated formation, an underlying structure of the arc arm, or whether there are other similar structures in this helical arm. Ultimately, this discovery turns the Sagittarius arm into an “excellent laboratory for examining star formation on scales large enough to compare with extragalactic observations.”
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