What To Know
- It maps the positions and movements of more than a billion stars in the Milky Way.
- Traditionally, the last major collision in the Milky Way, called the Gaia-Sausage-Enceladus (GSE), was thought to have occurred between eight and eleven billion years ago.
- Even such a small object can have a significant impact when it collides with a large galaxy like ours.
Scientists have recently made fascinating discoveries about the history of the Milky Way using observations from the European Space Agency’s (ESA) Gaia space telescope. These findings challenge what we thought we knew about galactic collisions and the growth of our galaxy.
The Milky Way’s Galactic “Wrinkles”
The Milky Way is not a static galaxy. Over billions of years, it has grown and evolved by merging with others. galaxies. These collisions are comparable to cosmic crashes that tear apart and consume smaller galaxies, incorporating their stars and material into the Milky Way. Each collision then leaves traces in the distribution and movement of stars. The Gaia space telescope is an essential tool for astronomers. It maps the positions and movements of more than a billion stars in the Milky Way. This data then allows scientists to understand how our galaxy has evolved over time. In 2018, Gaia revealed for the first time “wrinkles” in the distribution of stars. These wrinkles are areas where stars have unusual movementscreating distinct patterns that are the imprints of past collisions. In other words, these structures are like ripples left behind by ancient galactic collisions. By studying these ripples, scientists can then trace historical events that shaped our galaxy.
Visualization of a “wrinkled” halo of stars around the Milky Way. Credits: Halo stars: ESA/Gaia/DPAC; Milky Way and Magellanic Clouds: Stefan Payne-Wardenaar
A Revision of Galactic History
To understand these wrinkles, the researchers compared Gaia data with simulations of different galactic mergers. Traditionally, the last major collision in the Milky Way, called the Gaia-Sausage-Enceladus (GSE), was thought to have occurred between eight and eleven billion years ago. However, the recent Gaia data suggest a significant revision to this timeline. Specifically, the researchers found that the current wrinkles could only be so distinct if they were caused by a more recent event. If they came from an eight-billion-year-old collision, they would be too scattered to be observed distinctly. A new collision, called the Virgo radial merger, would have occurred only about 2.7 billion yearsmuch more recently than expected. Researchers believe this recent collision involved a dwarf galaxymuch smaller than our Milky Way, and containing fewer stars and matter. However, even such a small object can have a significant impact when it collides with a large galaxy like ours. This discovery This changes our understanding of the Milky Way’s evolution. Instead of believing that our galaxy underwent its last major merger billions of years ago, we now know that it has continued to evolve more recently. This means that many models and ideas about its growth need to be revised.
