How big is the Milky Way? Chinese scientists have discovered that the Milky Way is even bigger than imagined!

Chinese scientists recently used the APOGEE near-infrared stellar spectrum survey data to reconstruct the complete radial density distribution of stars in the Milky Way from the inside to the outside for the first time. The direct measurement results show that "the Milky Way is larger than previously assumed." The relevant research results have been published in the international authoritative academic journal Nature Astronomy.

Lian Jianhui, the first author of the article and associate professor at the Southwest Institute of Astronomy of Yunnan University, introduced that based on the new stellar surface density distribution, the research team found that the half-light radius of the Milky Way (the radius that contains half of the total luminosity of the galaxy) is almost twice the previous estimate (about 19,000 light-years), and is basically consistent with the radius of nearby galaxies of the same mass, indicating that the Milky Way is a typical disk galaxy in terms of galaxy size.

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The Milky Way is the home of mankind. For a long time, researchers have been able to carefully analyze the evolutionary history of the Milky Way 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 difficulties in studying the structure of the Milky Way is that the solar system is almost located in the disk plane of the Milky Way, and dust extinction seriously affects the observation of the direction of the main part of the Milky Way (the inner disk and the galactic center), "making any astronomical observation based on the optical band powerless."

"Since the effect of dust extinction on photons with longer wavelengths decreases rapidly, observations in the near-infrared band can alleviate this problem to a great extent." Lian Jianhui said that with the advancement of astronomical observation technology in recent years, especially the development of large-scale near-infrared stellar spectrum surveys, it has provided unprecedented opportunities to solve this problem.

Based on the world's first large-scale near-infrared stellar spectral survey APOGEE, the researchers conducted a comprehensive analysis of the inhomogeneities of APOGEE survey observations, the characteristics of dust and stars, and systematically reconstructed for the first time the true and complete surface density distribution of stars of different ages in the Milky Way from the core to the outer disk. The results show that the disk structure of the Milky Way conforms to the classical exponential distribution in the outer disk region; however, in the inner disk region, the star density remains almost flat, significantly deviating from the exponential distribution of the outer disk.

"In the past, based on the hypothesis of the exponential disk, people found that the half-light radius of the Milky Way (about 10,000 light-years) is smaller than that of galaxies of the same mass, and is 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 cross-comparison studies of the Milky Way and extragalactic galaxies, which will have an important impact on related research on the Milky Way.

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Source: Xinhua News Agency

Editor: Wang Mengru

Proofread by Xu Lailinlin