Mapping the Milky Way in Motion: Revealing the Galaxy’s Six-Dimensional Skeleton of Star Formation
This White Paper, led by Loredana Prisinzano, lays out a vision for understanding how star formation is shaped by the large-scale motions of the Milky Way in the coming decades. Rather than viewing our Galaxy as a static spiral, the authors argue that it should be understood as a dynamic system, constantly stirred by waves, warps, and gravitational interactions. Their central goal is to reconstruct what they call the “6D skeleton” of star formation: a map that combines the three-dimensional positions of young stars with their three-dimensional motions. Such a framework would allow astronomers to connect where stars form with how the Galaxy itself moves and evolves.
Key Science Questions
The paper begins by posing three key science questions. First, it asks how large-scale dynamical features, such as warps in the Galactic disk or vertical waves rippling through it, might trigger or regulate star formation. Second, it considers whether star-forming regions arise mainly from local, random processes, like feedback from nearby massive stars, or whether they are instead coordinated by Galaxy-wide dynamical events. Finally, it questions whether stars form only in dense clusters or whether they can also originate in more diffuse, elongated structures known as “stellar strings.” These questions set the stage for rethinking star formation as a process influenced by both local physics and global Galactic dynamics.
State of the Art: A Dynamic Milky Way
In reviewing the current state of the field, the authors emphasize how recent data, especially from the Gaia mission, have transformed our picture of the Milky Way. Observations have revealed that the Galactic disk is not calm or symmetric but instead shows clear signs of being out of equilibrium. Features such as spiral arms, a central bar, and a warped outer disk are now known to coexist with vertical asymmetries and wave-like motions. Young stellar objects, which are still close to their birthplaces, trace these structures particularly well and act as signposts of where star formation is happening today. However, because we observe the Milky Way from within, many aspects of its global structure, especially on the far side of the Galaxy, remain uncertain.
Scientific Challenges: Mapping the Galaxy in 6D
The authors then describe the main scientific challenges ahead. One of the most important is building a complete six-dimensional map of young stars across the Galaxy, combining positions with velocities. While Gaia has revolutionized studies near the Sun, much of the distant Milky Way is still poorly mapped because dust blocks optical light. Future surveys from facilities like the Vera C. Rubin Observatory and the Nancy Grace Roman Telescope will help by detecting large numbers of faint, low-mass young stars, which make up the majority of the stellar population. Looking further ahead, the proposed GaiaNIR mission could use infrared measurements to peer through dust and finally uncover the Galaxy’s hidden structure.
The Role of Stellar Ages and Star Formation Histories
Another major theme of the paper is the importance of stellar ages. By determining how old stars are across different regions, astronomers can reconstruct the Star Formation History of the Milky Way. Coherent structures made of stars with similar ages may point to a common dynamical origin, such as waves induced by satellite galaxies or the Galaxy’s own gravitational potential. The authors explain that age distributions can help distinguish between “bursty” star formation episodes, possibly driven by extreme events, and more continuous, self-regulated star formation sustained over billions of years. Understanding how feedback from young stars either shuts down or promotes further star formation is a key part of this challenge.
Technology Developments and the Road Ahead
Finally, the paper turns to the technological developments needed to achieve these goals. While deep imaging surveys are planned well into the 2040s, the authors stress that comparable spectroscopic facilities are missing. They argue for a new wide-field, ground-based spectroscopic telescope capable of measuring precise radial velocities and stellar properties for millions of young, low-mass stars, especially in dusty regions of the Galactic Plane. Extending these observations into the near-infrared is essential for reaching the far side of the Milky Way. Combined with future space missions, such a facility would complete the six-dimensional picture of our Galaxy and allow astronomers to truly understand how its dynamic structure shapes the birth of stars.
Source: Prisinzano
