Nanjing University astronomy has always been the dream of thousands of students. In their hearts, it is like the brightest star in the vast sky.
At 21:00 on April 10, 2019, the global press conference announced a "pioneering" major achievement - the first black hole photo! The appearance of this "picture" makes people see the real appearance of black hole for the first time, which is another ultimate verification of Einstein's general relativity and another milestone in the long journey to the universe.
There are 16 Chinese scientists involved in the 10-year-long project, including Professor Li Zhiyuan from the school of astronomy and space science, Nanjing University. In addition, Zhao Shanshan, a doctoral student in the school of astronomy and space science of Nantah, was supported by the National Overseas Studies Foundation and participated in the project in the Netherlands as a joint doctoral student.
The first photo of the black hole at the center of M87 Galaxy (source: eht collaboration)
A year later, after the first black hole photo, Nanjing University and Harvard worked together to draw the most accurate structural map of the galaxy, which once again attracted widespread attention.
Scientific American, a famous magazine, recently published a cover article entitled "new vision of the galaxy" jointly written by Mark Reid, a senior astronomer at Harvard Smithsonian astrophysics center in the United States and Professor Zheng Xingwu, an academician of the American Academy of Sciences, and professor of the school of astronomy and space science of Nanjing University, summarizing the two of them and K The international team led by Professor Karl Menten has spent 15 years studying the structure of the galaxy.
The team used very long baseline interference technology to accurately measure the distance and self motion 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 rotation speed around the center of the galaxy, and drew the structure map of the whole new galaxy with a scale of 100000 x 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. The main reason is that the diameter of the Milky way is estimated to be about 100000-180000 light-years. Our solar system is far away from the center of the Milky way, and its position is close to the central plane of the Galactic channel. Therefore, all the spiral arms we see are overlapped and projected on the celestial sphere, which cannot be distinguished. 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 serious extinction to the optical radiation of the celestial bodies on the spiral arm of the galaxy. The large optical telescope can only see the celestial bodies within 6000 light-years on the silver disk, which is far smaller than the size of the galaxy.
With the rise of radio and infrared astronomy. Astronomers have found that in addition to the objects with optical radiation, there are more radio and infrared objects that are invisible in the optics, as well as the molecular gas and dust that breed them in the formation area of massive stars on the spiral arm of the galaxy. They can be used as the tracer objects of the structure of the galaxy. What's more, radio and infrared radiation can penetrate the dense dust on the Galactic surface, allowing us to 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 of young objects in the massive star forming region, some basic problems of the structure of the Milky way are still unsolved, such as how many spiral arms the Milky way has, the exact position and movement of the sun in the Milky way, etc.
At the beginning of the 21st century, 22 astronomers from eight countries, including China, the United States, Germany, Italy, the Netherlands, South Korea, Japan and Poland, planned and established the major scientific plan of "the survey of the remaining treasures of the rod and arm structure of the galaxy" (Bessel for short in Chinese).
Bessel plans to use a very long baseline array with an equivalent aperture of earth diameter to directly measure the distance and self motion of maser sources in the massive star forming region by means of geometric trigonometric parallax. 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 map of the galaxy is finally drawn.
The Chinese members of the Bessel project research team are from Nanjing University, Zijinshan Observatory, Shanghai Observatory and the national time service center.
In 2003, Dr. Xu ye and Prof. Zheng Xingwu from the school of astronomy and space science of Nanjing University, Dr. Reid from Harvard Smithsonian Center of Astrophysics in the United States and Prof. Mendon from Max Planck Institute of radio astronomy in Germany cooperated to measure the trigonometric parallax and self motion of methanol (CH3OH) maser in w3oh in the great mass star forming region of Yingxian arm successfully for the first time by using very long baseline interference technology The distance of massive 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 celestial body in history.
By the end of 2019, Chinese astronomers have observed and analyzed 85 of the 163 target maser sources planned by Bessel. Bessel project has published 35 papers in internationally renowned astronomical and astrophysical journals, including 16 papers 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.
Text source: Nanjing University news network, top university
Wang Runyu