In the latest issue of Scientific American (April 1), a cover introduction entitled "new views on the structure of the galaxy" was published by Mark Reid, senior astronomer of Harvard Smithsonian astrophysics center and academician of the American Academy of Sciences, and Zheng Xingwu, Professor of the school of astronomy and space science of Nanjing University. In this paper, they and the international team led by Professor Karl menten of the Max Planck Institute of radio astronomy in Germany have spent 15 years on the observation and study of the galactic structure. They used very long baseline interferometer (VLBI) to measure the exact distance and self motion of the massive star forming region located on the spiral arm of the Milky way, draw a new spiral arm structure map of the Milky way and accurately determine the parameters of the Milky way. This map is the most accurate structural map of the Milky way at the position of the spiral arm so far. It clearly shows that the Milky way is a rod spiral galaxy with four spiral arms (the solar system is located in the local arm independent of the four main spiral arms). It completely solves the major scientific problem of how many spiral arms there are in the Milky way, which has been debated for a long time in astronomy.
As a core member of the Chinese team of the project, researcher Wu Yuanwei of the national time service center precisely measured the precise position and self motion of about 30 massive stars, and located the Sagittarius carina, a main spiral arm of the galaxy Arm) has made great contribution to the new image of the spiral arm of the galaxy. Relevant academic papers were published in Astrophysics journal in 2019, with the national time service center as the first completion unit, among which the galaxy structure review paper was published in Astrophysics journal in 2019, and the national time service center as the sixth completion unit. This work has been supported by the National Natural Science Foundation of China, the "light of the west" of the Chinese Academy of Sciences and the talent program of the Chinese Academy of Sciences.
　　
The Bessel project uses the VLBA very long baseline interferometry array of the United States, which takes six years and more than 5000 hours to observe. It accurately determines the structure and kinematic characteristics of the rods and spiral arms in the galactic disk. By modeling the position and motion of these massive young stars, the researchers determined the distance between the solar system and the center of the galaxy, 8150 ± 150 The second gap (26600 light-years) is smaller than the 8500 second gap recommended by IAU more than ten years ago; the sun is about 20 light-years away from the central plane of the silver disk, smaller than the previous estimate of 82 light-years; the rotation speed of the galaxy is 236 km / s, which is about 8 times the speed of the earth around the sun. Based on this distance and rotation speed, the researchers estimated that the sun's position took 212 million years to rotate around the center of the galaxy.
The high-precision VLBI astrometry technology used in the project can also be used for geodesy, earth orientation parameters and world time UT1 measurement. The 3 × 13m zfs-vlbi2010 system built by the national time service center is expected to pass the three-stage acceptance of retransmission satellite navigation this year and be used for world time UT1 measurement and navigation satellite VLBI observation.
(source: website of national time service center of Chinese Academy of Sciences)