Evolution of the local spiral structure of the Milky Way revealed by open clusters

TL;DR

This study uses a large catalogue of open clusters from Gaia EDR3 to investigate the structure and evolution of the Milky Way's spiral arms, suggesting they are long-lived and consistent with density wave theory.

Contribution

It provides observational evidence supporting the long-lived nature of the Milky Way's spiral arms using open cluster data, challenging dynamic spiral mechanisms.

Findings

Spiral arms are compatible with a long-lived pattern over 80 million years.

The Local Arm is likely a major, long-lived arm segment.

Density wave theory better explains the observed properties of open clusters.

Abstract

The structure and evolution of the spiral arms of our Milky Way are basic but long-standing questions in astronomy. In particular, the lifetime of spiral arms is still a puzzle and has not been well constrained from observations. In this work, we aim to inspect these issues using a large catalogue of open clusters. We compiled a catalogue of 3794 open clusters based on Gaia EDR3. A majority of these clusters have accurately determined parallaxes, proper motions, and radial velocities. The age parameters for these open clusters are collected from references or calculated in this work. In order to understand the nearby spiral structure and its evolution, we analysed the distributions, kinematic properties, vertical distributions, and regressed properties of subsamples of open clusters. We find evidence that the nearby spiral arms are compatible with a long-lived spiral pattern and might have remained approximately stable for the past 80 million years. In particular, the Local Arm, where our Sun is currently located, is also suggested to be long-lived in nature and probably a major arm segment of the Milky Way. The evolutionary characteristics of nearby spiral arms show that the dynamic spiral mechanism might be not prevalent for our Galaxy. Instead, density wave theory is more consistent with the observational properties of open clusters.