Milky Way galaxy can be larger than expected: study

This photo taken on Sept. 13, 2023 shows the Milky Way at the Altun Mountains National Nature Reserve in northwest China's Xinjiang Uygur Autonomous Region. (Xinhua/Hao Zhao)

KUNMING, July 12 (Xinhua) -- The Milky Way galaxy can be larger than previously expected and have a more complex radial structure, according to scientists.

The study, conducted by researchers from Yunnan University and several international institutes, was recently published in Nature Astronomy.

Using data from stellar spectroscopic surveys, researchers constructed a radial density distribution of stars from the inner to the outer regions of the Galaxy, measuring the Galaxy's radius.

The result indicates that the Galactic disk structure in the outer disk region conforms to a classical exponential distribution while the inner disk region remains nearly flat. This finding is distinct from the long-standing assumption of a single exponential disk for the Galaxy, according to Lian Jianhui, a researcher at Yunnan University.

Lian said the study can impact measuring the Galaxy's key physical properties. Based on the assumption in the past, the half-light radius of the Galaxy, within which half of its luminosity is contained, was estimated to be about 10,000 light-years. The radius was extraordinarily smaller compared to galaxies of similar mass, and thus, the Galaxy was classified as a compact galaxy.

However, based on the complex density distribution proposed in the study, the Galaxy's half-light radius is 19,000 light-years, almost in line with the radius of nearby galaxies of similar mass. This indicates that the Galaxy is a typical disk galaxy in terms of size, said Lian.

Lian said the study contributes to understanding the Galaxy's overall structure and evolution.