A team of Chinese space scientists, hailing from the Purple Mountain Observatory and the National Astronomical Observatories, have recently made a groundbreaking discovery that challenges the long-held view of the Milky Way galaxy's structure. In a recent paper published in The Astrophysical Journal, the team describes their comprehensive analysis of multiple sources of data, aimed at uncovering the true shape of our galaxy.
For decades, astronomers have depicted the Milky Way as a spiral galaxy with a central bulge and four prominent spiraling arms, accompanied by several smaller branching arms. However, recent advancements in telescope technology have revealed that the vast majority of galaxies can be categorized into one of three shapes: spiral, irregular, or elliptical, with most possessing two primary arms that split into smaller spirals.
The Chinese team's findings suggest that the traditional view of the Milky Way having four arms is flawed, leading to new questions about the true shape of our galaxy. As technology continues to improve and new discoveries are made, the study of the Milky Way will undoubtedly continue to evolve and expand, providing exciting new insights into the mysteries of our galactic home.
The observed splitting of spiral arms in galaxies has led researchers to theorize that such events may have resulted from collisions with other galaxies or clusters. In light of these findings, the traditional depiction of the Milky Way as a spiral galaxy with four arms has come under scrutiny, with suggestions that it would be an extremely rare occurrence requiring unique attributes.
The latest research by Chinese space scientists challenges the notion that the Milky Way has four arms, and instead suggests that it likely has just two main arms, similar to most other galaxies. The team arrived at this conclusion by analyzing data from a new generation of space instruments, which utilize advanced technology to accurately measure the distance between individual stars and the observer. One such instrument employs long baseline interferometry, allowing for precise measurements of the distances to stars emitting microwaves, and the team used it to measure 200 such stars to begin building a map of the Milky Way.
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| HI emission as a function of LSR radial velocity and Galactic longitude. The colored dots are HMSFR masers with parallax measurements: Norma Arm (orange), Sagittarius Arm (cyan), Carina Arm (green), Local Arm (blue), Perseus Arm (magenta), and Outer Arm (red). The white dots indicate spurs or sources for which the arm assignment is unclear. The HI emission is from the HI4PI survey (HI4PI Collaboration et al. 2016). The subfigure presents a zoomed-in view of the red box, in which the masers are assigned to the Norma Arm (orange crosses) and the Scutum Arm (orange triangles) by R19, respectively, while here they are assigned to the same arm, i.e., the Norma Arm. Credit: The Astrophysical Journal (2023). DOI: 10.3847/1538-4357/acc45c |
The team's findings underscore the evolving nature of our understanding of the Milky Way's shape and composition, and highlight the critical role that technological advancements continue to play in deepening our understanding of the universe.
In their quest to determine the true shape of the Milky Way, the Chinese research team leveraged data from a range of sources, including the Gaia space observatory. Specifically, they focused on O-B stars, which are particularly useful due to their minimal movement after formation, and analyzed data on 24,000 such stars. They also incorporated data on nearly a thousand open cluster stars, thanks to Gaia.
Using this data, the team developed a map of the Milky Way and fit the arrangement of stars to a spiral. Their findings suggest that the Milky Way is a barred spiral with two primary arms extending from the central bar. These arms are surrounded by shorter, more distant, and irregular arms that are not connected to the main structure. The team's work thus further illuminates our understanding of the galaxy's shape and provides valuable insights for future research endeavors.
Reference:
Y. Xu et al, What Does the Milky Way Look Like?, The Astrophysical Journal (2023). DOI: 10.3847/1538-4357/acc45c