Amazing warp structure of the Milky Way stellar disk

In the early morning of the 5th, at the time of the New Year, the international scientific journal Nature Astronomy published a major research result online. For the first time, astronomers showed the amazing warping structure of the outer galaxy of the Milky Way through observations of stars. This achievement updates people’s perception of the shape of the Milky Way and provides a key clue to how people ultimately understand how large disk galaxies like the Milky Way are formed and evolved.

“The stellar disk of the Milky Way seems to be a generally flat disk before the rich data is obtained, but this is not the case. In theory, the galactic disk has been in an unstable state.” The author of the above-mentioned research paper, Deng Licai, chief scientist of the National Astronomical Observatory’s Stellar and Stellar System team and director of the Department of Astronomy at the West China Normal University, said in an interview with the Science and Technology Daily that at the outer disk, the huge galaxies will gradually roll up or down, forming a whole close to the potato chips. The same bending state. Astronomers call this shape a “warp” of the galaxy disk, which can be seen directly on the lateral river galaxies.

But since humans are themselves on the galaxies of the Milky Way, it is quite difficult to study the structure of the Milky Way’s stellar disks. This is “I don’t know the true face of the mountain, only in this mountain.”

However, a large number of observations indicate that about one-third of the outer galaxies of the river show more or less warped shapes. According to this, the families guessed, is the Galaxy also the same?

In fact, radio observations have long revealed that the gas disk of the Milky Way exhibits a warped structure. The stellar disk of the Milky Way is similar to the structure of the gas disk. Does it also exhibit a warped structure? “Because gas and stars are controlled by the same gravitational field, they should show the same warp structure, but there is no direct evidence about the shape of the stellar disk.” Deng Licai said.

“This is because knowing the distance of the outer disk of the Milky Way can determine the shape of the outer disk, but the distance of the outer disk of the Milky Way is very large and it is very difficult to measure. It requires accurate and bright enough standard trace stars.” The first author of the above research paper Dr. Chen Xiaoxuan from the National Astronomical Observatory said that Cepheid Variable Star is the key to the breakthrough in this research. It helps astronomers effectively measure the distance of the outer disk of the Milky Way.

“The Cepheid variable star is a kind of medium-quality young pulsating variable star. Compared with the sun, the Cepheid variable star is 3-20 times heavier and brighter about 9 million times. Because their pulsation period is strictly related to luminosity, it can be used for precision. Measuring distance, the accuracy can reach 3%-5%.” Chen Xiaoyu explained.

Prior to the above research work, Chen Xiaoyu led the release of the first infrared all-weather star watch, which included 34,769 newly discovered variable stars, of which 1312 were galaxy sacred variable stars, more than the discovery of astronomers in the past 100 years. The sum of the Milky Way’s Cepheid variable stars has laid the foundation for the successful unveiling of the precise structure of the Milky Way silver plate. “This star-like precious star is an excellent tracer that indicates the shape of the young stellar disk of the Milky Way.” Chen Xiaoyu said.

“Dust extinction is the biggest obstacle to measuring the distance between the stars of the Milky Way silver plate. The interstellar dust like smog makes it difficult to measure the distance of stars, especially in the traditional optical band. But infrared multi-window research can greatly alleviate this difficulty. Our success has benefited from our group’s experience in the study of extinction laws,” explains Dr. Wang Shu from Peking University, the co-author of the above research paper.

Chen Xiaoyu told reporters that the overall sample of this study has 2,330 Milky Way Cepheid variable stars, including 1312 found in the infrared and other star catalogs. “We selected 1339 of the samples. They lit up the galaxy covered by ‘smoke’ like a bright light.”

Chen Xiaoyu joined the National Astronomical Observatory’s “Star and Stellar System Group” in 2016. The team’s main work direction is the Galaxy research. The team also includes Liu Chao, a researcher at the National Astronomical Observatory, Professor Richard Dihe Ruisi from Macquarie University, Australia, and Beijing. Dr. Wang Shu, a university student, has long studied the structure of the Milky Way and the time domain of stars.

From the three-dimensional spatial distribution map, Chen Xiaoyu and the team found that the farther away from the center of the Milky Way, the more the deceased variable stars deviated from the silver plate, the overall “S” type; if facing the silver heart and let the North Silver face up, then the left hand side The silver plate will roll up (north) and the right hand side will be opposite. Not only that, but they also found that the warping from the center of the silver presents a complex precession phenomenon.

“The results show that the structure of the stellar disk of the Cepheid variable is very consistent with the structure of the gas disk of the Milky Way. More importantly, this warped ‘S’ shape also has a spiral pattern that gradually turns.” Richard Collaborator Professor Di He Ruisi pointed out.

Although warping often occurs in extragalactic galaxies, theorists do not agree with how it is formed. One possible explanation is that the outer disk is formed by some kind of torque. “The torque hypothesis can explain the complex warping precession phenomenon. Our observations tend to be dominated by the large internal disk torque. The results of the dynamics of the disk, our results are of great significance!” Liu Chao said.

“The warpage of the Milky Way disk was confirmed by stellar observations, which first updated the understanding of the shape of the Milky Way, and also provided decisive observational evidence of the origin of the disk, for us to finally understand how the giant galaxies like the Milky Way formed and Evolution provides key clues.” Deng Licai said excitedly.