The Edge of Our Galaxy Eluded Scientists for Years. They Finally Found It.

Key Points:

• Researchers from the University of Malta have pinpointed the Milky Way’s edge at its outermost star-formation site, approximately 40,000 light-years from the galactic center, marking the galaxy’s true boundary.
• The Milky Way exhibits a U-shaped stellar age profile where stars get younger moving outward from the center until a break point, beyond which stars are older due to migration from inner regions.
• Star formation in the outer disk drops sharply beyond this break, likely caused by factors such as the galaxy’s central bar dynamics, gas phase transitions, or the onset of a warp in the galactic disk.
• Analysis of over 100,000 giant stars from surveys like APOGEE-DR17, Gaia, and LAMOST-DR3 revealed that star ages and metallicity distributions support the idea of stellar migration and a complex interplay of galactic processes shaping the Milky Way’s structure.
• The findings clarify why star formation ceases at the galaxy’s edge, with cold, diffuse gas beyond the break being too sparse and low in energy to form new stars, effectively defining the Milky Way’s outer limit.