Chinese scientists recently used APOGEE near-infrared stellar spectral survey data analysis to reconstruct for the first time the complete radial density distribution of stars in the Milky Way from the inside out. The direct measurement results showed that "the Milky Way is larger than previously assumed". The relevant research results have been published in the internationally authoritative academic journal Nature Astronomy. The first author of the article, Associate Professor Lian Jianhui from the Southwest Institute of Astronomy at Yunnan University, introduced that based on the new stellar surface density distribution, the research team found that the half radius of the Milky Way (including half of the total luminosity of the galaxy) is almost twice the previously estimated (about 19000 light-years), and is basically consistent with the radius of neighboring galaxies of the same mass, indicating that the Milky Way is a typical disk galaxy in terms of galaxy size. The Milky Way is the home of humanity. For a long time, researchers have been able to analyze the evolution history of the Milky Way in detail by observing a large number of distinguishable stars, but they lack a clear understanding of the overall structure of the Milky Way. One of the main challenges in studying the structure of the Milky Way is that the solar system is almost located on the plane of the Milky Way's disk, and dust extinction seriously affects the observation of the main parts of the Milky Way (inner disk and galactic center) direction, making any astronomical observation based on optical bands powerless. Due to the rapid reduction of the impact of dust extinction on longer wavelength photons, observations in the near-infrared band can greatly alleviate this problem Lian Jianhui said that with the advancement of astronomical observation technology in recent years, especially the development of large-scale near-infrared stellar spectral surveys, unprecedented opportunities have been provided to solve this problem. Researchers conducted a comprehensive analysis of the non-uniformity, dust, and stellar characteristics observed during the international first large-scale near-infrared stellar spectral survey, APOGEE. For the first time, they systematically reconstructed the true and complete surface density distribution of stars of different ages in the Milky Way from the nucleus to the outer disk. The research results indicate that the disk structure of the Milky Way follows a classical exponential distribution in the outer disk region; However, in the inner disk region, the stellar density remains almost flat, significantly deviating from the exponential distribution of the outer disk. In the past, based on the assumption of an exponential disk, people found that the half light radius of the Milky Way (about 10000 light-years) was smaller than that of galaxies of the same mass, and it belonged to a compact galaxy Lian Jianhui said that the latest research has overturned this hypothesis and opened up new dimensions for measuring the overall physical properties of the Milky Way and studying the cross comparison between the Milky Way and extragalactic systems, which will have an important impact on related research on the Milky Way. (New Society)