“The milky first turn water cross-flow, star historians rushed to report the news”, Niu Lang weaving girl romantic dating of the Galaxy do not know how many people’s heartstrings? Walking under the stars, can not help thinking, this bright river of stars in the end how many unknowns waiting for us to explore? Looking up at the stars, you might ask, what does the structure of the Milky Way look like? How many stars are there in the Milky Way, and what are they doing all the time, and is there a regular pattern? It is these questions that have taken the astronomers from generation to generation on the path of science, revealing the truth of one deep universe after another, and driving the innovation of astronomical knowledge one after another.
Figure 1: The Milky Way “Arch Bridge” in Qinghai is visible in winter (photographed by Deng Licai).
Figure 2: Side and top views of the Milky Way, as well as the stream of stars passing through her (pictured from the web).
The Milky Way consists mainly of the silver heart and raised nuclear ball, the silver disk with a spin arm, and the silver halo scattered around the silver disk, of which the silver disk is the main component of the Milky Way, the Milky Way’s luminous matter, at least nine percent of the silver disk range.
Undulating Disc Star Team
Many years ago, astronomers have found that stars near the sun on the silver disk are so restless that, in addition to moving around the silver heart, you often come and walk around. In 2018, the author’s team analyzed the stars on the silver disk, for the first time in the range beyond the sun 16,000 light-years, from the perspective of speed to the milky galaxy’s uneasy side of the star, the star on the silver disk movement like water waves up and down, showing the star-waved star formation.
Figure 3: Map of the direction of star motion in different directions of the Milky Way (map: charcoal)
As shown in Figure 3, two teams of stars (motion substructures) show the motion of stars near the sun on the silver disk and 16,000 light-years away from the sun. On the left is a team of stars called the “North Near Structure”, which clearly shows the movement of their movements in the horizontal direction of the silver heart to humans, and the star team on the right is a group of asymmetrical structures near the sun, showing the vertical pace of the stars here.
In addition to the characteristics of motion, how old are these stars? Is it a young, energetic young man on the silver plate, or a late-year old life star? Has such two star teams been coming together to maintain such asymmetric motion? What kind of scientific story are carried behind them? A series of questions have caused researchers to be curious enough about the two star teams.
Just past 2019 was an astronomical data harvest year, with the Guo Shoujing Telescope (LAMOST) capturing more than 10 million spectrals, becoming the world’s first spectral survey to break the multi-million-magnitude spectrum, and ESA’s Gaia satellite releasing the cut-in speed information of about 1 billion stars. Machine learning supports the acquisition of age data for millions of stars, and such a wealth of resources has helped astronomers continue to study these two interesting teams of stars on the silver disk.
Figure 4: LAMOST and the Galaxy (Photograph: Yuan Fengfang)
What year did the final star stay?
After a more detailed analysis of the “Northern Near Structure” region (corresponding to the star team on the third left) of about 10,000 light-years from the sun and about 0.16 million light-years from the silver disk plane, the researchers carved a time-evolution sequence into the star team, known as the “Northern Near Structure”, based on data on the age of the stars in LAMOST. A comprehensive age survey of the star team found that the star family had young, old, age-wide, but overall a relatively young family, and found that the “survival time” of the “northern near-structure” could be detected by humans was about 6 billion years (Figure V), This means that scientists have calculated that this asymmetrical “north-north near-structure” will be “curvy” about 6 billion years after its existence. Because as stars age, the star grows at a larger rate, and the star may dissolve on its own about 6 billion years later.
Figure 5: The “survival time” detected by the radial velocity substructure (refers to the time of existence of asymmetrical features detected by humans, not the death of a star). The asymmetrical features of the corresponding star squads in the white box “disappeared” after 6 billion years.
As a result of the study, scientists further identified the asymmetrical structure of the second star team, which runs upward on both sides of the sun’s outer north and south, and found that the asymmetric structure is traceable to 8 billion years of “survival time” or “sensitive timescale”, that is, 8 billion years after the existence of this structure, the region will still have stellar activity. It’s just that we can no longer detect this asymmetrical feature.
The moon is cloudy and clear, and the stars are sad and happy. It may be 6 billion, 8 billion years, but after all, there will be a breakaway drama in the time and space of the Milky Way.
With the “survival time” and age span of these stellar teams, we can gradually trace their evolutionary history, thus promoting astronomers’ understanding of the basic understanding of the history of the Integration of the Milky Way.
Figure 6: The “survival time” chart of the vertical velocity substructure detected, which scientists found found that the stars in the second star-bound constellation (inside the frame above) were disbanded after 8 billion years, and they were still moving, but we couldn’t see asymmetric features.
Why stars “ups and downs”
Astronomy has gradually transitioned from static depiction of the universe to dynamically depicting the universe, and astronomers have analyzed not only the asymmetrical structure of stars, but also the changing characteristics of these substructures, by classifying and analyzing the ranks of stars of different ages. So what kind of physical mechanism sedits the asymmetry of these substructures on the silver plate? What exactly are these star teams’ ups and downs, sad and rejoicing “pushers behind”?
By calculating and comparing, the researchers believe that the agitating of the star by the spiral arm in the Milky Way and the gravitational pull of the milk are important factors in the asymmetric structure on the silver disk, and that the molecular clouds on the silver disk, the outer disks of the equilibrium state caused by the collapse of the isolated overdensity region, and the warping characteristics of the outer disks may have contributed to these “asymmetric structures”. Star members aggregate, disturbances in external neighbor dwarf galaxies, or magical dark matter halos may also be part of the factor. The team is likely to be under the command of a unified and complex distribution function, and the uneasiness within the Milky Way, coupled with external interactions, has led to the current motion of stars in different families in different parts of the Milky Way, but this series of mysteries awaits astronomers to continue to explore.
In the past two years, the author’s research team has carried out multi-directional traceof the stars in the 16,000 light-year area of the sun, including physical interpretation, chemical diagnosis, time domain analysis, and finally obtained the volatile motion characteristics, age changes and the length of time the entire structure has been detected by humans. This shows us that the milky galaxy on which humans depend is really too unsettling and too difficult.
“The beauty of physics is that God hides the greatest secrets and wealth,” Mr. Yang said. The fascinating thing about astrophysics is that we constantly explore and excavate the secrets that God hides, and in the process of exploring the structure, origin and evolution of the universe, we will continue to approach the real physical picture of space, thus making many unexpected discoveries. In the next few years, the team will rely on LAMOST, Gaia and other cruise slats to bring the human line of sight to the more distant and deep sky. Our journey is the beautiful and beautiful sea of stars, and never stop …
Thank you: Thanks to Liu Chao, researcher of the National Observatory, and Li Haining, Associate Researcher, for their valuable comments on this article.
1。 Wang H. -F. et al. , 3D Asymmetrical motions of the outer Galactic disc with LAMOST K giant stars, 2018a, MNRAS, 477, 2858
2。 Wang H. -F. et al. , Mapping the Milky Way with LAMOST-III. Mlynesspatial structure in the outer disc, 2018b, MNRAS, 478, 3367
3。 Wang H. -F. et al. , Shima the Disk with the LAMOST and Gaia Red clump sample. Ⅲ. A new velocity substructure and time stamps of the disk asymmetry in the disk between 12-15 kpc, 2019a, APJ, 884, 135
4。 Wang H. -F. et al. , Shima the Disk with the LAMOST and Gaia Red clump sample. Ⅱ. 3D asymmetrical kinematics of mono-age populations in the disk 6-14 kpc, 2020a, MNRAS, 491, 2104
5。 L?pez-Corredoira M. , et al. , Gaia-DR2 extended kinematical maps
Part II: Dynamics in the disk sing sing sing sing sings and vertical velocities, 2020, A and A, in press
6。 Xu Y. , et al. , Rings and Radial Waves in the disk of the milky way, 2015, APJ, 801, 105
7。 Xiang M. -S. et al. , The Ages and Masses of A Million-disk Main-Turn Sequenceoff and Subgiant Stars from the LAMOST Spectro scopic Surveys, 2017, APJS, 232, 2
About the author
Wang Haifeng: Postdoctoral Fellow, Southwest Astronomy Research Institute of Yunnan University, Young Researcher of LAMOST, Chinese Academy of Sciences. Research areas: the chemical dynamics of the Milky Way, clusters and interstellar media, astronomical data analysis, etc.
Li Shuang: Engineer of the National Observatory of the Chinese Academy of Sciences, Director of Publicity, LAMOST Center for Operation and Development.