A team of Chinese scientists has discovered that the Milky Way galaxy is significantly larger than previously estimated. By analyzing near-infrared stellar spectroscopic data from the APOGEE survey, the researchers determined that the Milky Way’s half-light radius extends about 19,000 light-years from its center—nearly twice the distance commonly accepted before.
Lead author Lian Jianhui, associate professor at the Southwestern Institute for Astronomy Research, Yunnan University, explained that this new measurement aligns the Milky Way with other local disk galaxies of similar mass. “Our findings suggest that the Milky Way is a typical disk galaxy in terms of its size,” said Lian. The study was recently published in the journal Nature Astronomy.
Historically, studying the Milky Way’s structure has been challenging due to the position of the sun within the galaxy, which causes high line-of-sight extinction toward its densest regions. Observing large samples of stars across wide spatial ranges has also been time-consuming. However, near-infrared observations mitigate the effects of dust extinction, allowing for more accurate data collection.
“Because dust extinction decreases rapidly at longer wavelengths, near-infrared observations greatly alleviate the issue of obscured regions,” Lian noted. Utilizing this advantage, the researchers reconstructed the complete surface density distribution of stars of different ages from the galactic bulge to the outer disk—a first in astronomical studies.
The team discovered that while the Milky Way’s outer disk follows a classical exponential distribution, the inner disk exhibits a nearly flat stellar density, deviating from the expected pattern. This revelation challenges previous assumptions. “In the past, under the assumption of an exponential disk, the Milky Way’s half-light radius was estimated at about 10,000 light-years, categorizing it as a compact galaxy,” Lian explained. “Our latest research overturns this assumption, opening new dimensions for measuring the galaxy’s overall physical properties.”
This groundbreaking study not only reshapes our understanding of the Milky Way’s size but also its classification among galaxies. The findings pave the way for future research into the structure and evolution of our home galaxy, offering deeper insights into the cosmos.
Reference(s):
Chinese scientists say Milky Way larger than previously thought
cgtn.com
