Chinese scientists say Milky Way larger than previously thought

A team of Chinese scientists has found that the Milky Way is larger than previously thought after analyzing APOGEE near-infrared stellar spectroscopic data.

Based on the new stellar surface density distribution, the researchers found that the Milky Way's half-light radius is about 19,000 light-years, nearly twice as large as previously estimated. This radius is roughly consistent with that of local disk galaxies of similar mass, indicating the Milky Way is a typical disk galaxy in terms of its size.

For a long time, researchers have analyzed the evolutionary history of the Milky Way by observing a large number of discernible stars as the sun's position results in high line-of-sight extinction towards the densest region in the galaxy, and collecting data from large samples of stars over a wide spatial range is costly in terms of observing time.

"Due to the rapid decrease in the effect of dust extinction on longer wavelength photons, observations in the near-infrared band can greatly alleviate this issue," said Lian Jianhui, the lead author of the study, which was published in the journal Nature Astronomy, and also associate professor from Southwestern Institute for Astronomy Research, Yunnan University.

The researchers reconstructed the complete surface density distribution of stars of different ages in the Milky Way from the bulge to the outer disk for the first time. 

The study revealed that the disk structure of the Milky Way conforms to a classical exponential distribution in the outer disk region. However, in the inner disk region, the stellar density remains nearly flat, significantly deviating from the exponential distribution observed in the outer disk.

"In the past, based on the assumption of an exponential disk, it was found that the Milky Way's half-light radius (about 10,000 light-years) was smaller than that of galaxies of similar mass, categorizing it as a compact galaxy," said Lian. 

The latest research has overturned this assumption, opening up new dimensions for measuring the overall physical properties of the Milky Way.