Guo Jing's "most" telescope has demonstrated its strong observation ability again. Based on the seventh batch of low resolution spectral data released by LAMOST, Chinese researchers have found 734 extremely cold dwarfs, all of which are candidates for brown dwarfs. Relevant research results were recently published in the journal Astronomy and astrophysics. "Extremely cold dwarfs are small in mass, red in color and dark in brightness. It is very difficult to observe them, and the requirements for observation equipment are very high." On April 26, Luo Ali, a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, explained in an interview with reporters. Extremely cold dwarfs refer to the spectral type of late type m (M7 ~ M9) and l, t and Y dwarfs. From the perspective of spectral type, the extremely cold dwarfs of late type m and early type l may be brown dwarfs or ordinary low mass stars, which depends on their own mass. Roali said that extremely cold dwarfs are very important to study the chemical reactions and physical processes inside stars at the junction of stars and brown dwarfs. Because of their dim brightness, telescopes are more likely to observe earth like planets with very small mass around them, so they are also ideal candidates for searching for earth like planets. At the same time, brown dwarf is named for its rusty brown surface. It is an alternative celestial body. It is neither a star nor a planet. Its mass is between stars and planets. It can also be said that it is a star whose evolution has failed. Brown dwarfs are the bridge between stars and planets. They play a very important role in the formation history of the Milky way, the initial mass function, the study of the atmosphere of hot planets and so on. The research team screened out more than 10000 late type M-type star data from more than 700000 M-type star data of LAMOST. Through manual inspection and comparison, 734 extremely cold dwarfs with kinematic age of about 300 million years and similar kinematic characteristics and metal abundance to galactic disk stars were finally selected. "The spectral information of two-thirds of the extreme cold dwarfs in the sample is obtained for the first time, and the spectral data have good consistency. Therefore, this is a very rare large sample of extreme cold dwarfs with complete parameter information so far." Roali said. More importantly, these extremely cold dwarfs are very close to the earth. 80% of the member stars are within 300 light-years, and the farthest is only 1174 light-years. "These extremely cold dwarfs are candidates for brown dwarfs, of which 77 have obvious lithium absorption lines. They are very likely to be brown dwarfs." Roali said that six of them are wide-range binaries discovered for the first time. In theory, their companion stars may be less massive, so their companion stars are more likely to be brown dwarfs. Roali said that the sample has important scientific application value for the study of the properties and evolution of extremely cold dwarfs, especially brown dwarfs, which are very difficult to observe. In the near future, with the accumulation of LAMOST spectral data and the launch operation of China Space Telescope (CSST), more and more distant brown dwarfs may be detected, which will bring more opportunities for the study of the formation mechanism and internal properties of relatively vacant brown dwarfs in the field of stellar physics. (Xinhua News Agency)