The Milky Way

The Milky Way, as our home galaxy, provides a unique opportunity for in-depth study. Researchers in our division are deeply involved in pushing the boundaries of our understanding of the galaxy, with the European Space Agency's (ESA) Gaia mission being a prime example. Since mid-2014, Gaia has been gathering data on over a billion stars, creating a comprehensive dynamical map of the Milky Way that extends far beyond our Solar neighborhood. The Gaia mission is expected to deliver an all-sky map that will help us address fundamental questions about the origin and evolution of our galaxy, offering insights that can be applied to galaxies throughout the universe.

Gaia is equipped with advanced instruments for measuring the positions, motions, and photometric properties of celestial objects, but its spectroscopic capabilities are somewhat limited. This is where ground-based observations become essential. Our participation in the Gaia-ESO Survey, conducted at the Very Large Telescope in Chile, is crucial for complementing Gaia’s data. This survey has observed 100,000 stars across different stellar populations, providing detailed information on their elemental compositions and helping to calibrate the data obtained by Gaia. We co-lead work packages on the high-resolution part of the survey and calibrations with the help of benchmark stars. High-precision spectroscopy remains a cornerstone of modern astrophysics, enabling researchers to study the chemical evolution of the Milky Way and characterize stars that host planetary systems. The Gaia-ESO Survey, for instance, has meticulously compiled atomic and molecular data to ensure accurate abundance analysis for up to 10⁵ stars. These efforts are supported by laboratory astrophysics and databases that provide the necessary atomic transition data for interpreting spectra collected by both ground- and space-based instruments.

The second Gaia data release provided astrometry and photometry of unprecedented precision for about 1.3 billion stars, unveiling intricate details of the Hertzsprung-Russell diagram and offering deeper insights into the various stages of stellar evolution within the Milky Way. This data has also enabled researchers to explore the relationship between stellar kinematics and evolution, particularly in the galaxy’s halo. The third Gaia data release further enriched this dataset with high-quality astrophysical parameters for half a billion stars, supporting studies that range from analyzing the Milky Way’s rotation curve to investigating exoplanet host stars.

In addition, our team is contributing to the 4MOST project, a large spectroscopic survey set to observe up to 20 million stars using the VISTA telescope at Paranal Observatory in Chile. Scheduled to begin in 2024, 4MOST will significantly expand the spectroscopic data available for studying the Milky Way, enhancing our understanding of its stellar populations and overall structure.

Moreover, the 4MOST Stellar Clusters Survey will target nearly all the accessible globular and open clusters within the galaxy, providing critical data for understanding how these clusters form, evolve, and contribute to the Milky Way’s development. This survey will also help refine our understanding of stellar physics by providing highly accurate empirical isochrones, essential for measuring stellar ages.

Our research is supported by the Swedish National Space Agency, the Knut and Alice Wallenberg Foundation, the European Science Foundation, and the European Commission. By combining the vast data from Gaia with extensive ground-based observations, we continue to advance our understanding of the Milky Way, shedding light on the fundamental processes that shape our galaxy.