Like many other galaxies, the highly oblate Milky Way exhibits a grandiose spiral structure. The spiral arms, which mainly contain many gas clouds and young stars, have been mapped over the past 60 years, primarily on the basis of observations with radio telescopes.
One of the relatively close arms, the arc arm, now appears to have a noticeable curvature of about 50 degrees. Other galaxies sometimes show such broken structures, but this is the first time we’ve also seen this in our own Milky Way.
An astronomer led by Michael Kuhn of the California Institute of Technology discovered the broken arm by searching data from the Spitzer Telescope for newborn stars. Then they used data from Gaia to determine the exact distances of those stars. In this way I reconstruct a 3D map, in which the oblique part of the arc arm is clearly visible.
The newly discovered “bulge” of the arm of Sagittarius contains a large number of star-forming regions. Four of them are the famous nebulae that can actually be seen through binoculars in the night sky: the Lagoon Nebula, the Trifid Nebula, the Omega Nebula, the Eagle Nebula.
It is not yet clear why the Milky Way broke his arm. The new findings were published last summer in the European Trade Journal Astronomy and Astrophysics.
Photo: NASA/ESA/Hubble Heritage Team
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