Summary
In the baryonic world, galaxies are the bricks of the universe, but their distribution in the universe is not random. On a large scale, the distribution of galaxies is network like; On a small scale, galaxies often exist in pairs, such as the Milky Way and the Andromeda Nebula in the local galaxy cluster. Galaxies will eventually merge, and this merging process is one of the main pathways for galaxy growth. Observational studies of galaxy pairs can help people understand the interactions and growth processes of galaxies. The article focuses on the observations of galaxy pairs in modern galaxy surveys, particularly the role played by China's major scientific project, the Guo Shoujing Telescope.
Galaxies and their distribution in the universe
Until the early 20th century, the galaxies in people's eyes were just shining clouds in the Milky Way, known as "nebulae". There is very little knowledge about these nebulae. The astronomical century debate held in 1920 marked the beginning of research on extragalactic systems. The Great Debate of the Century was a debate between astronomers Harlow Shapley and Heber Doust Curtis regarding the understanding of "nebulae". Shapley believed that galaxies are celestial bodies within the Milky Way, and the Milky Way is the entire universe. Curtis believed that galaxies are extragalactic objects of the same scale as the Milky Way, and exist like islands in the universe. This debate did not have a clear result until 1924: scientists such as Hubble calculated the distance of the Andromeda Nebula and determined that these "bright clouds" were actually massive objects of the same scale as our Milky Way galaxy. Subsequently, in 1929, Hubble discovered and confirmed Hubble's law, which states that the distance of a galaxy is proportional to its rate of regression, meaning that the universe is expanding. Based on Hubble's law, the distance of a galaxy on a large scale can be accurately determined by its redshift (retrograde velocity). Afterwards, galaxy astronomy developed rapidly, and people's understanding of the universe made a qualitative leap. Now, we know that galaxies are the fundamental building blocks of the visible universe, composed of hundreds of billions of stars and containing matter such as gas, dust, and even dark matter whose physical essence we currently do not know.
Detailed link: https://wuli.iphy.ac.cn/cn/article/pdf/preview/10.7693/wl20150404.pdf