Using data from the APOGEE survey, astronomers from the Potsdam Leibniz Institute for Astrophysics, the University of Vienna, and the Paris Observatory reconstructed the properties of “hidden” stars within the Milky Way’s disk.

“With each dramatic increase in the number of stars, our understanding of the Milky Way has improved,” said Dr. Sergei Khopelskov of the Potsdam Leibniz Institute for Astrophysics and his colleagues.

“From the earliest observations to increasingly advanced space and ground-based telescopes, each milestone has revealed new layers of the galaxy’s complex structure and motion.”

“Although the amount of star research continues to expand, our view of the Milky Way remains very vague because most of the stars we can study are concentrated around the Sun.”

“This discrepancy is primarily due to fundamental limitations in our observations resulting from our position in the central plane of the Milky Way’s disk.”

“At our location, the amount of stars we might be able to observe is limited by their brightness, but also by the possibility of interstellar medium blocking or dimming, called annihilation. It is affected by dust and gas.”

The authors have developed an innovative method to fill gaps in our understanding of the Milky Way’s structure.

“Rather than relying solely on observations of individual stars, we can use the entire orbits of actual stars to represent the structure and dynamics of galaxies,” they explained.

“As stars move around the center of the galaxy, they serve as a tool for mapping areas of the galaxy that our telescopes cannot directly reach, including areas on the opposite side of the Milky Way.”

“Using a model of the Milky Way’s mass distribution and observed star positions and velocities, we not only calculated the stars’ orbits, but more importantly, how much mass is associated with each orbit. I measured what I should do.”

Using a new technique, we apply it to a large sample of stars using spectroscopic parameters from the star. APOGEE surveyThis is part of the Sloan Digital Sky Survey, in which researchers mapped the kinematics of stars across the Milky Way.

They revealed the complex motion of stars within the bar region, unhindered by distance measurement uncertainties.

Astronomers quantified the galaxy’s mass-weighted chemical abundance and age structure by reconstructing the star’s orbit using real Milky Way stars with precisely determined parameters.

This approach avoids the challenges posed by dense interior regions and the disappearance of the interstellar medium, and provides a comprehensive view of the stellar population, including previously unobservable regions on the Milky Way’s far side.

“You can look at this approach from a different perspective,” Dr. Hopelskov said.

“Imagine that for every star we observe, there is a large sample of stars that follow the exact same orbits but were not captured by surveys for various reasons.”

“What we’re doing is reconstructing the positions, velocities and stellar parameters of these invisible stars and filling in the missing parts of the galaxy’s structure.”

“The new data strongly suggest that the Milky Way formed in two distinct stages, as evidenced by the different age and chemical abundance relationships.”

“The inner disk lies well inside the Sun’s radius and formed relatively quickly during the early stages of galactic evolution.”

“About 6 to 7 billion years ago, the outer disk began to assemble, rapidly expanding the radial extent of the Milky Way and forming its current structure.”