doi.org/10.1051/0004-6361/202558144
Credibility: 989
#Milk Way
The Milky Way, our home galaxy, doesn’t end abruptly with a sharp edge
Its disk of stars gradually fades until it disappears into space.
For a long time, astronomers struggled to define exactly how far the region where new stars are born extends.
Now, an international team of researchers has managed to clearly identify this limit: active star formation in the Milky Way stops, on average, about 40,000 light-years from the galaxy’s center.
The scientists reached this conclusion by studying the age of the stars.
They observed that, as you move away from the center, the stars become younger until approximately 35,000 to 40,000 light-years.
After this distance, the trend reverses: the stars become older again.
This “U”-shaped pattern reveals the true limit of the region where the galaxy is still producing new stars.
Within this radius, there is enough cool gas to constantly form stars.
Beyond it, star formation drops drastically.
This discovery confirms that galaxies grow from the inside out.
Star formation begins in the denser central regions and, over time, spreads to the outer areas.
However, in the Milky Way, this process has a cutoff point.
The stars we find beyond this edge were not born there.
They migrated from the interior of the galaxy over billions of years.
This radial migration occurs thanks to spiral waves that travel through the galactic disk.
Like surfers catching waves, the stars gain energy by repeatedly interacting with the spiral arms and slowly move away from their birthplace.
Therefore, the outermost stars tend to be the oldest: they have had more time to travel.
Furthermore, these stars orbit in an almost circular fashion, indicating that they were not ejected by collisions with other galaxies, but rather by normal internal processes of the Milky Way.
To map this edge, the researchers analyzed more than 100,000 bright giant stars.
They used spectroscopy data from the LAMOST and APOGEE surveys, combined with precise measurements from the European Space Agency’s Gaia satellite, which is mapping the position and movement of billions of stars in our galaxy.
They then compared this data with advanced simulations of galactic evolution performed on supercomputers.
These simulations reproduced the same “U” pattern when considering a sharp drop in star formation efficiency from a certain distance.
Dr. Karl Fiteni, lead author of the study (currently at the University of Insubria, Italy), explained that the extent of the star-forming disk was an open question in galactic archaeology.
Now, by mapping how the ages of stars change across the disk, they have obtained a clear and quantitative answer.
Professor Joseph Caruana, from the University of Malta, supervisor of the work, highlighted that the current data allow for the use of increasingly precise stellar ages to decipher the history of the Milky Way, opening a new era of discoveries about our galaxy.
It is not yet known exactly why star formation drops so much at this distance.
It could be the influence of the galaxy’s central bar, which concentrates gas in certain regions, or the effect of the outer fold of the disk, which disrupts the conditions necessary for star birth.
The important thing is that the pattern of ages has proven to be a reliable indicator of the true limit of stellar activity.
In the future, surveys like 4MOST and WEAVE will provide even more detailed data, allowing us to refine these measurements and better understand what determines the edge of our galaxy.
This study shows how the ages of stars, which were previously difficult to measure precisely, have become a powerful tool for reconstructing the history of galaxies.
By tracking where and when stars were born and how they moved over billions of years, scientists are assembling an increasingly clear picture of how the Milky Way formed and evolved.
This research, published in the journal Astronomy & Astrophysics, represents an important advance in understanding the structure and evolution of our own galaxy, revealing that it has a hidden edge that we have finally been able to map.
Published in 05/06/2026 15h40
Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.
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