Scientists at the Max Planck Institute for Extraterrestrial Physics have used APOGEE data to build the most accurate model to date of the Milky Way's central region and have discovered a new structure there: a ring of metal-rich stars.
Studying the structure of our galaxy has always been a challenge because we have to look inside it. Our solar system is close to one arm of the galactic disk. From this vantage point, many of the stars in our galaxy are hidden from view by dense clouds of gas and dust. The central region is particularly difficult to see. For this reason, scientists are actively studying other galaxies, paying more attention to those that resemble the Milky Way.
The Milky Way is a spiral galaxy with a bar. In other galaxies with this structure, scientists have repeatedly noticed a ring of forming stars in the central region. The question has arisen: does the Milky Way have such a ring?
For a decade, scientists at the Max Planck Institute for Extraterrestrial Physics (Germany) have been collecting astronomical observational data and building computer models of our galaxy. In their new study, they worked with results from the APOGEE survey and Gaia observations. The astronomers compared the parameters of more than 30 000 stars and built a computer model of their movements. The result is the most accurate map of the Galaxy's central region. With its help, for the first time managed to discern a slowly rotating bar (slow bar) and the curved barge, shaped like a peanut. The results have been published in an Astronomy & Astrophysics article.
The APOGEE survey is a large-scale spectroscopic survey of the sky. It was part of the Sloan Digital Sky Survey (SDSS). Observations were made in the near-infrared. This range makes it possible to see through dense clouds of gas and dust. APOGEE provided information about the composition, position, Doppler shift and approximate age of stars in the central Milky Way, while Gaia provided the exact coordinates, direction and speed.
By combining the data, scientists were able to calculate the full orbits of the stars in the central region. This made it possible to simulate the Galactic region hidden by the balge. Thanks to the accuracy and completeness of the new model's data, a coveted ring of younger, metal-rich stars was revealed around the central bar. And most importantly, their concentration appeared to be higher near the galactic plane. So, active star formation in the ring continued after the formation of the bar, so their age can be used to analyse the evolution of the Milky Way's central structures. The authors of the study estimate that the average age of the stars in the ring suggests that the galactic bar formed at least seven billion years ago.
It is not yet known if there is a connection between this ring of stars and the spiral arms of the Milky Way, or if the thin ring is fed by gas flows, as is the case in other spiral galaxies.
Hopefully, astronomers will be able to answer these questions when the next generation of telescopes is launched. The new instruments will allow scientists to make more accurate observations. More sophisticated computer models can be developed from this data. Our Galaxy still has many mysteries to solve.
