Gaia data reveals remnants of Milky Way mergers

"We discovered five small clusters which we believe are remnants of five merger events," researcher Helmer Koppelman said.
By Brooks Hays  |  June 12, 2018 at 12:55 PM
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June 12 (UPI) -- Using the latest Gaia data, astronomers at the University of Groningen in the Netherlands have identified several groups of stars shaped by past galactic mergers.

The Gaia mission is an effort by scientists to compile the largest and most precise 3D space catalog in history. Through two data releases, the second of which occurred in April, Gaia has detailed the precise positions and movements of millions of stars.

Scientists are already using this rich source of data to better understand the relationships and organization structures that define groups of stars. The relationships and structural patterns identified among groups of distant stars can help scientists study the Milky Way's past and its evolution over time.

Astronomers know that galaxies collide and merge, but scientists aren't certain whether the Milky Way is the product of lots of small mergers or a few big collisions.

The Gaia mission is helping researchers find out.

"We collected information from stars within 3,000 light years of the sun, as the accuracy of the position and movement is highest for stars that are near us," astronomer Helmer Koppelman said in a news release.

For this particular study, scientists wanted to focus only on stars within the Milky Way's halo.

"These stars move around the center of the disk, so are easily identified," Koppelman said.

Koppelman and his research partners were able to filter 6,000 halo stars from the dataset. Then, by analyzing the stars' velocities and trajectories, researchers were able to identify relationships, or connections, among the different stars.

"We discovered five small clusters which we believe are remnants of five merger events," Koppelman said.

However, the analysis showed several of the stars within the five clusters were also related.

"These stars form a huge 'blob' with a retrograde movement compared to the disk," Koppelman said. "This suggests they are the result of a merger with a large galaxy. In fact, we believe that this merger event must have remodelled the disk in our Milky Way."

Researchers shared their discovery on Tuesday in the Astrophysical Journal Letters.

The team of astronomers is now working to more accurately characterize the large merger that produced the stellar blob.

"At this point in time, we can say that our Milky Way was shaped by a massive merger event and some smaller mergers," Koppelman said.

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