Defining where the Milky Way ends has always been challenging because its disk does not stop abruptly -- it gradually fades into space. Now, for the first time, an international team of astronomers has pinpointed the boundary of the Galaxy's star-forming disk by examining the ages of stars. Their findings show that most star formation in the Milky Way takes place within about 40,000 light-years of the Galactic Center. To reach this conclusion, researchers combined measurements of the ages of bright giant stars with advanced simulations of galaxy evolution. This approach revealed a distinct "U-shaped" pattern in how stellar ages are distributed, which marks the outer limit of active star formation in our Galaxy. "The extent of the Milky Way's star-forming disc has long been an open question in Galactic archaeology; by mapping how stellar ages change across the disc, we now have a clear, quantitative answer," remarked the paper's lead author, Dr. Karl Fiteni, now based at the University of Insubria.…