An international team led by researchers from the National Institute of Astrophysics has created the most detailed map ever produced of the spiral structure of the Milky Way within 16,000 light years of the Sun, using the position and brightness of about 600,000 young stars measured by the Gaia satellite. of the European Space Agency
The Milky Way, a galaxy of which the Sun is part along with hundreds of billions of other stars, is formed by a disk in which most of these stars reside, arranged in the form of a spiral . Since the 1950s, astronomers have been trying to define the number and structure of the “arms” of this spiral, which is no easy feat due to our position as observers within the disk itself. This scenario is now changing thanks to Gaia , the satellite of the European Space Agency which is carrying out a cosmic census of the positions, distances and motions of nearly two billion stars with unparalleled precision.
The new map, based on the latest data from Gaia , released last December, indicates that the geometric shape of the spiral arms of the Milky Way is different from that predicted by many of the models proposed in the past. The results concern the arm of Perseus , one of the main structures that form the galactic spiral, and the local arm , a less pronounced structure, where – among other stars – is also the Sun.
«The local arm appears to be more extensive than previously thought, reaching an extension of at least 26 thousand light years. The Perseus arm, on the other hand, has a different geometry compared to that envisaged by many previous models, with a larger opening angle “, explains Eloisa Poggio , first author of the article published in Astronomy & Astrophysics , researcher at the Côte d’Azur Observatory, in France, and associated with the National Institute of Astrophysics (INAF) of Turin.
The study is based on the largest sample of young stars – about 600,000 – ever used to map the spiral arms within 16,000 light-years of the Sun, a distance equal to about one-sixth the diameter of the Milky Way, which measures 100,000 light-years. . By analyzing the spatial distribution of populations of young stars in the galaxy’s disk, the team created maps of areas that are more or less star-rich than average density. The densest areas, also called “overdensity”, appear organized in a coherent way, tracing the segments of the spiral arms closest to the solar system.
“This study would not have been possible before Gaia,” adds co-author Ronald Drimmel of INAF of Turin. “Gaia has provided us with precise position measurements for an unprecedented amount of data, with a number of objects that have enough statistics to be able to apply the overdensity mapping method in the disk.”
The team compiled the map using mainly young, bright stars, which map out the areas where star-forming activity is most active, such as the spiral arms. In addition to these, they also analyzed the distribution of other young stellar components, such as variable stars called Cepheids and open star clusters.
“We know that the Milky Way is a spiral galaxy,” Poggio emphasizes. “However, even if this may seem paradoxical, in our galaxy we do not know exactly how many spiral arms there are, where they are located exactly, what their geometric shape is, because the Solar System is immersed in the galactic disk, making the mapping of the galaxy ‘on a large scale’ much more difficult. Yet having a map of the spiral arms is crucial for many aspects: for example to study the different physical phenomena that occur in the disk in relation to them ».
The new galactic spiral map in our cosmic neighborhood represents a first step towards understanding these structures, whose origin and dynamic nature have long been – and still are – much debated.
“Our study helps to delineate an increasingly detailed map of the spiral structure of the Milky Way,” concludes Drimmel. “With the future data of Gaia we plan to extend this map to greater distances, and to compare the position of the spiral arms obtained with the motions of the stars in the disk.”
To know more:
- Read on Astronomy & Astrophysics the article ” Galactic spiral structure revealed by Gaia EDR3 “, by E. Poggio, R. Drimmel, T. Cantat-Gaudin, P. Ramos, V. Ripepi, E. Zari, R. Andrae, R . Blomme, L. Chemin, G. Clementini, F. Figueras, M. Fouesneau, Y. Frémat, A. Lobel, DJ Marshall, T. Muraveva and M. Romero-Gómez
Watch Claudia Mignone’s interview with Eloisa Poggio on MediaInaf Tv :
Featured image: The new map of our cosmic neighborhood: the areas in red show the regions richest in stars compared to the average density, and the areas in blue show the regions poorest in stars compared to the average. The black curves indicate the spiral structure of the Milky Way. Distances are given in kiloparsecs: 1 kpc = 3,260 light-years (click to enlarge). Credits: Poggio et al. 2021
Provided by INAF