Nanjing University and Harvard University
Looking up at the starry sky for 15 years
Finally, the galaxy was mapped
The most accurate structure chart so far
Let us know the true face of Lushan Mountain in this mountain
A new report for you
Report of Guangming Daily on April 22
What shape is the Milky way? Chinese and foreign scientists have drawn up the most accurate structure map of the Milky Way galaxy so far
Galactic Structure
Zheng Xingwu and mark Reid
Scientific American recently published a cover article entitled "new vision of the galaxy" jointly written by Mark Reid, senior astronomer of Harvard Smithsonian astrophysics center, academician of the American Academy of Sciences, and Zheng Xingwu, Professor of the school of astronomy and space science of Nanjing University, summarizing the two of them and Professor Karl menden of the Max Planck Institute of radio astronomy in Germany International team, after 15 years of research on the structure of the galaxy.
The team used very long baseline interference technology to accurately measure the self motion and distance of nearly 200 massive star forming regions on the silver plate, obtained the structure of the spiral arm of the galaxy, the position of the solar system and its speed of rotation around the center of the galaxy, and drew the structure map of the new galaxy with a scale of 100000 × 100000 light-years. This is the most accurate structural map of the Milky way so far. It clearly shows that the Milky way is a rod spiral galaxy with four spiral arms. It completely solves the major scientific problem of how many spiral arms the Milky way has in astronomy.
The structure of the galaxy is one of the most important scientific problems in astronomy. According to Professor Zheng Xingwu, the main reason is that the diameter of the galaxy is estimated to be about 100000-180000 light-years, and the solar system is far away from the center of the galaxy, and its position is close to the center of the silver disk, so the spiral arms we see are all overlapped projected on the celestial sphere and cannot be distinguished. It is "because we do not know the true face of Lushan Mountain, but only because we are in this mountain". However, if we can accurately measure the distance from enough celestial bodies on the spiral arm to the sun, we can completely sketch the spiral arm structure of the galaxy from the inside to the outside. However, there are dense dust and gas distributed on the silver disk, which cause very serious extinction to the optical radiation of the celestial bodies on the spiral arm of the galaxy. Even with the use of large optical telescope, we can only see the objects within 6000 light-years on the silver disk, which is far smaller than the size of the galaxy.
The real extensive and in-depth observation and study of the structure of the Milky way is due to the rise of radio and infrared astronomy in the 1950s. Astronomers use radio and infrared telescopes to find that in addition to the objects with optical radiation in the formation area of massive stars on the spiral arm of the galaxy, there are more radio and infrared radiation objects that are not visible in the optics, as well as the cold molecular gases and dust that breed them, which can be used as the tracer objects of the galactic structure. What's more, radio and infrared radiation can penetrate the diffuse interstellar medium (gas and dust) on the Galactic surface, and let us reach the edge of the galaxy.
After nearly half a century of observation and research, astronomers generally believe that the Milky way is a rod spiral galaxy. However, due to the inaccuracy of measuring the distance between the young objects in the massive star forming area, some basic problems of the structure of the galaxy, such as how many spiral arms there are in the galaxy, the exact position and movement of the sun in the galaxy, are still unsolved.
At the beginning of the 21st century, 22 astronomers from 8 countries, including China, the United States, Germany, Italy, the Netherlands, South Korea, Japan and Poland, planned and established the major scientific plan of "Bexel" for the survey of galactic rod and spiral arm structures. The Bessel project uses a very long baseline interference array with an equivalent aperture of the earth's diameter to directly measure the self motion of maser sources in the massive star forming region by means of geometric trigonometric parallax method, so as to obtain their accurate distances (maser sources are cosmic laser point sources with a bright temperature of more than 100 million degrees, or even 100 million degrees).
Since 2003, the research team has measured the self motion and distance of maser sources in 163 massive star forming regions on the silver disk. Combined with 37 maser sources measured by other international clusters, the team has obtained the distance and self motion of nearly 200 massive star forming regions in the galaxy. The distribution of these massive star forming regions on the silver plate clearly delineates four main spiral arms, namely, the Perseid arm, the Centaur ship bottom arm, the cunchi arm and the shield Centaur arm. Combined with the observation data of infrared, carbon monoxide and a large number of young celestial bodies, the structure of the Milky way is finally mapped out. It is a rod spiral galaxy with four spiral arms. In extragalactic systems, rod vortex galaxy is a large family. The Milky way is an ordinary galaxy and a beautiful galaxy with symmetrical arms.
Scientists have found that the solar system we live in is not on the four main rotating arms, but very close to a local arm independent of the four main rotating arms. This local arm, located between the Perseus arm and the humanoid - ship bottom arm, is about 20000 light-years long, much larger than previously estimated. Its shape and abundant massive star forming area can be compared with the other four main spiral arms. The local arm may not be an isolated arm segment, but it is most likely a part of the adjacent fairy arm and humanoid bottom arm. The distance between the sun and the galactic center is 26000 light-years, and the rotation speed around the galactic center is 236 km / s, that is to say, it takes about 212 million years to make a circle. The sun is almost in the central plane of the silver plate, and the vertical distance from the central plane is about 20 light-years, smaller than the previous estimate of 82 light-years.
It is reported that the Chinese members of the "Bezier project" research team are from Nanjing University, Zijinshan Observatory, Shanghai Observatory and the national time service center. In the past 15 years, the Chinese team has played an important role in the "Bezier plan" based on the principles of CO initiation, CO organization, complementary resources and sharing of achievements.
In 2003, Dr. Xu ye and Prof. Zheng Xingwu from the school of astronomy and space science of Nanjing University, Dr. reed from Harvard Smithsonian Center of Astrophysics in the United States and Prof. menden from Max Planck Institute of radio astronomy in Germany cooperated to measure the trigonometric parallax and self motion of methanol maser in w3oh in the great mass star forming region of the British celestial arm successfully for the first time by using very long baseline interference technology The distance to measure the star forming area is 6360 ± 40 light-years, and the measurement accuracy is as high as 2%. This is the most accurate distance measurement for such a distant object in history. From the self and apparent velocities of the maser, the three-dimensional motion of the massive star forming region in the galaxy is obtained, and the kinematic properties of the spiral arm of the galaxy are studied. This work indicates the feasibility of directly measuring the structure and motion of the spiral arm in the galaxy. This achievement was published in science as a cover paper in January 2006, which is the pioneering work of "Bessel plan". Since then, Chinese members have proposed and participated in leading experimental observations, and the research results have laid a solid foundation for the implementation of the Bessel plan.
By the end of 2019, Chinese astronomers have observed and analyzed 85 of the 163 target maser sources of the Bessel plan. The Bessel project has published 35 papers in internationally renowned astronomical and astrophysical journals, of which 16 papers have been published by Chinese astronomers. By participating in this major scientific program, the development of VLB astrometry in China has been promoted, and young astronomers have been trained, so that they are at the forefront of VLB astrometry in the world.
Source: Nanjing University, Guangming Daily