The disrupting and growing open cluster spiral arm patterns of the Milky Way

TL;DR

This study uses Gaia DR3 data and dynamical simulations to analyze open cluster distributions, revealing that the Milky Way's spiral arms are dynamic, transient structures rather than fixed, quasi-stationary patterns.

Contribution

It provides new insights into the transient nature of Galactic spiral arms and challenges the traditional density wave theory using recent astrometric data and simulations.

Findings

No age pattern in spiral arms traced by open clusters

Spiral arm pattern speeds align with the rotation curve

Local arm appears to be growing

Abstract

Star clusters provide unique advantages for investigating Galactic spiral arms, particularly due to their precise ages, positions, and kinematic properties, which are further enhanced by ongoing updates from the astrometric data. In this study, we employ the latest extensive catalogue of open clusters from Gaia DR3 to examine the positional deviations of clusters belonging to different age groups. Additionally, we employ dynamical simulations to probe the evolutionary behavior of spiral arm positions. Our analysis reveals an absence of a theoretical age pattern in the spiral arms traced by open clusters, and the pattern speeds of the spiral arms are consistent with the rotation curve. Both of these results do not align with the predictions of quasi-stationary density wave theory, suggesting a more dynamic or transient arm scenario for the Milky Way. From this perspective, combined with vertex deviation estimates, it appears that the Local arm is in a state of growth. In contrast, the Sagittarius-Carina arm and the Perseus arm exhibit opposing trends. Consequently, we speculate that the Galactic stellar disk does not exhibit a grand-design spiral pattern with a fixed pattern speed, but rather manifests as a multi-armed structure with arms that continuously emerge and dissipate.