The argument is over!
Chinese scientists confirm that the anti-galactic heart structure of the Milky Way originated from the silver disk
This discovery put an end to another controversy over the stellar waves rippling the Milky Way.
On May 8th, the reporter learned from the National Astronomical Observatory of the Chinese Academy of Sciences that researchers from the station and China West Normal University used data from the Guo Shoujing Telescope (LAMOST) and the Gaia satellite (Gaia) to analyze the anti-galactic center of the Milky Way. Research on the origin of substructures such as the Monoceros ring, Triangulum-Andromeda star stream and A13 has revealed that the anti-galactic substructure of the Milky Way is not a remnant of a dwarf galaxy accreted by the Milky Way, but a part of the outer disk of the Milky Way.
This conclusion puts an end to the long-standing controversy in the astronomical world about the origin of the anti-galactic sub-structure.
Related research results were published in "Astrophysical Journal".
As the name suggests, the so-called anti-galactic center refers to the area in the galaxy that is in the opposite direction to the galactic center.
Astronomers' research on the structure of the anti-galactic center is like traveling in the sky, starting from the center of the galactic center, casting a radial net, all the way to find the "structure flower" blooming thousands of stars.
At present, the substructures that astronomers have found in the anti-galactic direction of the Milky Way include the north near structure, the south center structure, the Monoceros ring, A13, and the Triangulum-Andromeda stream.
These substructures are arranged from the inside to the outside, from 39,000 light-years to 98,000 light-years, forming a unique landscape in the anti-galactic center direction.
Not only that, these stellar substructures also alternately appear on the north and south sides of the silver disk, which outlines the graceful undulations of the silver disk.
At the same time, the discovery of these substructures also allowed astronomers to re-understand our Milky Way.
It is not a smooth flat disk as traditionally recognized, but a restless galaxy of rippling stellar waves.
"But where did these anti-silver heart structures originate? Astronomers have been arguing about this." said Xue Xiangxiang, a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences.
Researchers took advantage of the large sample data observed by LAMOST in the anti-galactic center of the Milky Way, combined with the high-precision self-motion data of "Gaia" DR2, and searched for 589 stars from the Monoceros ring, the Triangulum-Andromeda star stream and the A13 structure. Member star.
"This is the largest sample of members of the anti-galactic substructure at present." said Li Jing, an associate professor in the School of Physics and Space Science at China West Normal University.
Like other spiral galaxies, the silver disk is considered to be composed of two parts, a thin disk and a thick disk.
The researchers conducted a "paternity test" of the chemical element content, motion characteristics, and energy angular momentum distribution of these member star samples with the silver disk, and were pleasantly surprised to find that these member stars and the silver disk have similar nearly circular motion orbits.
The metal abundance is similar to the thick disk star, which proves that these substructure member stars may come from the thick disk of the silver disk.
Further verification found that the alpha element abundance of these substructure member stars was significantly lower than that of the thick disk.
In this regard, Li Jing explained that this is because there is still a lot of cold gas in the outer disk of the Milky Way. Compared with the inner disk, the density of molecular clouds is low, the speed of star formation is slow, and the metal abundance of chemical elements has not increased sufficiently, so the abundance of alpha elements It is lower than the thick disk star.
"From the motion characteristics and chemical DNA identification, we speculate that these sub-structure member stars should belong to low alpha abundance metal-poor outer disk stars, which means that these anti-galactic sub-structures originated from the silver disk." Xue Xiangxiang said.
At the same time, these substructures are distributed in the range of 39,000 light-years to 97,800 light-years from the center of the Milky Way, which also proves that the outer disk component still exists at 97,800 light-years from the center of the galaxy.
This conclusion proves that the radius of the silver disk is at least 97,800 light-years, which is twice the size of the first known classic disk. This is in line with the research results obtained in 2018 based on LAMOST data, which expanded the Milky Way from the "second ring" to " The conclusions of "Five Rings" are consistent.
Li Jing said that this study confirmed that the anti-galactic sub-structure of the Milky Way originated from the silver disk. It also confirmed that the Monoceros ring, A13, and the Triangulum-Andromeda Nebula are part of the outer disk of the Milky Way. Controversy about the origin of the anti-yinxinzi structure since.
◎Our reporter Lu Chengkuan