A team of researchers led by the Leibniz Institute for Astrophysics Potsdam (AIP) has made significant strides in unveiling the hidden structure of our Milky Way galaxy. By examining the orbits of observed stars, they have reconstructed the properties of unseen stars that share the same orbital paths, shedding light on the mysterious regions of the galactic disk. These findings offer new insights into the galaxy's past, present, and future.
The study of our galaxy has evolved alongside advancements in observational technology. Early observations gave way to increasingly sophisticated space and ground-based telescopes, each unveiling more details of the Milky Way’s intricate structure and motion. However, our view remains limited, as most stars studied are located near the Sun. This limitation arises from our position within the galaxy's central plane, which restricts the number of observable stars and is further obscured by interstellar dust and gas that dims their light.
In collaboration with the University of Vienna and the Paris Observatory, researchers at AIP have developed an innovative method to overcome these observational constraints. Instead of relying only on direct star observations, the team utilized the entire orbits of stars to map the galaxy’s structure and dynamics. These stellar movements offer a means to probe regions beyond our observational reach, including areas on the far side of the galaxy.
By applying a model of the Milky Way's mass distribution along with the observed positions and velocities of stars, the team was able to calculate the orbits of stars and determine the associated mass of each orbit. Using a new technique applied to data from the APOGEE survey, part of the Sloan Digital Sky Survey, they were able to map stellar kinematics across the galaxy. This method allowed them to study the motion of stars in the galactic bar region without the uncertainty typically introduced by distance measurements.
The team’s innovative approach enabled them to reconstruct stellar orbits and determine the galaxy's mass-weighted chemical abundances and age structure. This method bypasses the challenges posed by dense regions and interstellar dust, providing a comprehensive view of stellar populations, including those previously hidden on the far side of the galaxy.
The findings, which have been published as three papers on the arXiv preprint server, suggest that the Milky Way formed in two distinct phases. The inner disk, located closer to the Sun, formed rapidly early in the galaxy’s evolution, while the outer disk began to assemble around 6–7 billion years ago, leading to the expansion of the galaxy and the shaping of its current structure.
