The Expanding 3 kpc Arms Are Neither Expanding nor Spiral Arms but X1 Orbits Driven by the Galactic Bar

Abstract

Near the center of our Milky Way is a bar-like structure and the so-called Expanding 3-kpc arms. We currently have limited knowledge of this important region, since we are about 8.2 kpc from the center and cannot directly observe it at optical wavelengths, owing to strong extinction from interstellar dust. Here we present extremely precise VLBI measurements of water maser sources from the BeSSeL Survey, where extinction is not a problem, which accurately determine the 3-dimensional locations and motions of three massive young stars. Combined with previous measurements, these stars delineate a trail of orbits outlining the Milky Way's Galactic Bar. We present the first measurements capturing the dynamics of quasi-elliptical (X1) orbits around the Galactic Bar. Our findings provide evidence substantiating the existence of such orbits populated by massive young stars. Our measurements of the position and velocity of a number of massive young stars, previously identified with the Expanding 3-kpc arms, show that they are more likely located in the X1 orbits about the Galactic Bar. Also, some stars previously assigned to the Norma spiral arm appear to be in these orbits, which suggests that this spiral arm does not extend past the end of the bar.

References in corpus (12)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Trigonometric Parallaxes Of High-Mass Star Forming Regions: Our View Of The Milky Way
• The Structure of the Milky Way's Bar Outside the Bulge
• Improved GRAVITY astrometric accuracy from modeling of optical aberrations
• Tracing the long bar with red-clump giants
• The Long Bar in the Milky Way. Corroboration of an old hypothesis
• Trigonometric Parallaxes of Massive Star Forming Regions: V. G23.01-0.41 and G23.44-0.18
• The long Galactic bar as seen by UKIDSS Galactic Plane Survey
• The First VERA Astrometry Catalog
• Gas Dynamics in the Galaxy: Total Mass Distribution and the Bar Pattern Speed
• Anomalous peculiar motions of high-mass young stars in the Scutum spiral arm
• Trigonometric Parallaxes of Four Star-forming Regions in the Distant Inner Galaxy

Cited by in corpus (2)

• Gas Transfer Between the Inner 3-kpc Disk and the Galactic Central Molecular Zone
• The Spiral Pattern Speed in the Milky Way Galaxy