The European Space Agency’s (ESA) Gaia mission has reached a monumental milestone: the completion of its primary mission to map the Milky Way galaxy. Over a decade in space, Gaia has collected over three trillion observations of two billion stars and other celestial objects, resulting in the most comprehensive and accurate map of our galaxy ever created. With its fuel reserves dwindling, Gaia is now preparing for retirement, leaving behind an invaluable legacy for astronomical research.
Gaia’s comprehensive data set has enabled scientists to construct a remarkably detailed visualization of the Milky Way, offering a glimpse of how our galaxy might appear from an external perspective. These visualizations showcase the galaxy’s intricate spiral structure, which appears less prominent than previously believed, and the central galactic bulge, home to the supermassive black hole Sagittarius A*.
The wealth of data gathered by Gaia has led to the discovery of a multitude of fascinating objects within our galaxy. In April 2024, scientists identified the most massive stellar-mass black hole in the Milky Way, located a mere 2,000 light-years from Earth. This followed the 2022 discovery of the closest-known black hole, a smaller object situated just 1,600 light-years away.
In June 2023, analysis of Gaia data suggested that interactions between the Milky Way and other galaxies might have occurred billions of years later than previously estimated, prompting a reassessment of existing theories about our galaxy’s evolution. According to Stefan Payne-Wardenaar, scientific visualizer at the Haus der Astronomie in Germany, “Gaia has changed our impression of the Milky Way. Even basic ideas have been revised, such as the rotation of our galaxy’s central bar, the warp of the disc, the detailed structure of spiral arms, and interstellar dust near the Sun.”
Gaia’s achievements extend beyond mapping stars. The mission has precisely measured the orbits of over 150,000 asteroids and generated a groundbreaking three-dimensional map of over one million quasars. While our understanding of the distant reaches of the Milky Way remains based on educated guesses due to limited data, Payne-Wardenaar notes that with the continued analysis of Gaia data, “our view of the Milky Way will become even more accurate.”
As Gaia nears the end of its operational life due to fuel depletion, it will be transitioned into a retirement orbit. In the coming weeks, the spacecraft will undergo a series of technological tests to prepare for this final maneuver. Even after its observational phase concludes, Gaia’s legacy will continue through future data releases. The next release is scheduled for 2025, with another planned for the end of the decade. To date, Gaia has generated 500 terabytes of data, representing only 5.5 years of its total observation period. Johannes Sahlmann, a Gaia project scientist, states, “After 11 years in space and surviving micrometeorite impacts and solar storms along the way, Gaia has finished collecting science data. Now all eyes turn towards the preparation of the next data releases.” The 2025 data release is expected to contain at least 500 terabytes of information, potentially including data on new exoplanets and binary star systems.
To prevent interference with other active spacecraft, Gaia will be passivated—rendered electrically inert—on March 27. This marks the end of an era for a mission that has revolutionized our understanding of the Milky Way and paved the way for future discoveries.
