Surprising Youthfulness: The Remarkable Stellar Bar in the Milky Way's Core

Our understanding of the history of our galaxy, the Milky Way, may require amendments. This comes after new discoveries indicate that a bar-shaped cluster of stars at the center is younger than was previously thought.

This bar, a significant characteristic of our galaxy, connects thousands of light-years and links the spiralling strands of stars in the galaxy. This gives them an appearance similar to water streams from a spinning lawn sprinkler. Computer-generated models of the evolution of the Milky Way have often proposed that this bar took form early in the 13-billion-year lifespan of the galaxy. However, recent findings now suggest that metal-rich stars within the bar indicate it completed formation a few billion years ago. The study submitted on November 28 is currently under review by Astronomy & Astrophysics Letters.

According to Samir Nepal, an astrophysicist from the Leibniz Institute for Astrophysics Potsdam in Germany, these metal-rich stars serve as fossil records of ancient stars, telling us the evolution of our galaxy.

Stars with a high proportion of metallic elements are remnants of exploded stars which scattered metals created from lighter elements. These scattered metals enrich the core of galaxies like the Milky Way, and thus, a new generation of metal-rich stars can only form deep inside galaxies. The Milky Way’s central spinning bar has been spreading some of these stars around our galaxy.

Using data from Gaia, a space telescope of the European Space Agency, Nepal and his team recreated the Milky Way's bar development by studying the spread of metal-rich stars. Like observing the path of baseballs to deduce the position of batters in a baseball game, even if one cannot see the home plate.

The researchers identified a sudden burst in star formation in the center of the galaxy that eased off about three billion years ago, by studying the ages of the metal-rich stars. This drop off seemingly signifies the end of the bar development phase, according to the team. They suggest the current bar is a stable feature that's about 10 billion years younger than the rest of the galaxy.

Cristina Chiappini, another astrophysicist with the Leibniz Institute, said the new insights are just the beginning of the data that will be retrieved from the Gaia telescope. If the revised estimate of the bar's age is confirmed, future models will have to account for why the bar formed later than initially considered.

Ortwin Gerhard from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who was not part of the research, explained that these findings are not only crucial for understanding our galaxy better but also for the potential they hold in studying bars in other galaxies. He stated that studying the Milky Way bar might provide valuable information about the evolution of bars across the universe based on data from the Gaia satellite.