Milky way galaxy shape
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The Shape of the Milky Way Galaxy
Milky Way Galaxy Structure: Spiral Arms and Central Bar
The Milky Way Galaxy is a complex and dynamic structure, primarily characterized by its spiral arms and central bar. Recent studies have provided a more detailed understanding of its morphology, revealing that the Milky Way has a multiple-arm structure. This includes two prominent arms, the Perseus and Norma Arms, in the inner regions, and several long, irregular arms such as the Centaurus, Sagittarius, Carina, Outer, and Local Arms extending outward .
Central Bar and Bulge: Boxy/Peanut (X) Shape
The central region of the Milky Way features a strong bar structure, which transitions from a peanut-shaped bulge to a thinner extended part ending around 5 kpc from the center . This bar is a significant component, containing about 30-40% of the total stellar mass of the galaxy. The bar's rotation speed is approximately 35-40 km/s/kpc, corresponding to a rotation period of 160-180 million years . The bulge itself exhibits a boxy or X-shaped structure, which is a common feature in barred spiral galaxies 478.
Influence of External Forces: Sagittarius Dwarf Galaxy Impact
The Milky Way's morphology is not solely a result of internal dynamics. The infall of the Sagittarius dwarf galaxy has significantly influenced the formation of the spiral arms and the central bar, as well as producing a flared outer disk . This interaction highlights the role of minor mergers in shaping the structure of galaxies, suggesting that such events are common and influential in the universe .
Local Spiral Structure: The Local Arm
Recent measurements have shown that the Local Arm of the Milky Way is larger and more significant than previously thought. Its pitch angle and star formation rate are comparable to those of the major spiral arms like Sagittarius and Perseus . This arm extends significantly along our line of sight, particularly towards the constellation Cygnus, forming the complex Cygnus X region .
Dark Matter Halo and Galactic Shape
The shape of the Milky Way is also influenced by its dark matter halo. Studies using self-interacting dark matter (SIDM) models suggest that the presence of baryonic feedback effects can alter the inner structure of the galaxy, although the overall shape remains consistent with predictions from collisionless cold dark matter models . The transition radius, where the shape of the total mass distribution begins to differ from that of the stellar mass distribution, is dependent on the SIDM cross-section .
Conclusion
The Milky Way Galaxy is a barred spiral galaxy with a complex structure that includes multiple spiral arms, a central bar, and a boxy/peanut-shaped bulge. External forces, such as the impact of the Sagittarius dwarf galaxy, have played a significant role in shaping its morphology. Advances in distance measurements and simulations continue to refine our understanding of the galaxy's structure, revealing the intricate and dynamic nature of our cosmic home.
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