The last major act of cannibalism by the Milky Way was recent

Space.com

New findings from the Gaia space telescope indicate the Milky Way may have cannibalized a small galaxy not too long ago, cosmically speaking.
In fact, the last major collision between our galaxy and another seems to have occurred billions of years later than previously suspected.
These bouts of galactic cannibalism also send “wrinkles” rippling through the Milky Way that affect different “families” of stars, with different origins, in different ways.
It is thought to have infused the Milky Way with stars on orbits that bring them close to the Galactic Center.
Since 2020, Thomas and his team have been comparing the Milky Way’s wrinkles to simulations of how galactic collisions and mergers could have created them.
“New wrinkles of stars form each time the stars swing back and forth through the center of the Milky Way.
This new research is the latest in a treasure trove of results emerging from Gaia data that are rewriting the history of the Milky Way.
“The Milky Way’s history is constantly being rewritten, in no small part, thanks to new data from Gaia,” Donlon concluded.

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Cosmologically speaking, new data from the Gaia space telescope suggests that not too long ago, the Milky Way may have eaten a small galaxy. The most recent significant collision between our galaxy and another appears to have happened billions of years later than previously thought.

Since our solar system’s spiral home has such a strong gravitational pull on smaller galaxies, it has long been known that the Milky Way grew through a series of violent collisions. The Milky Way’s main disk and its recognizable spiral arms are surrounded by a halo that is created when stars from the devoured galaxy collide. In addition to causing “wrinkles” to ripple through the Milky Way, these episodes of galactic cannibalism also have distinct effects on various “families” of stars based on their respective origins.

Gaia’s goal is to count the wrinkles in the Milky Way’s history by precisely determining the position and motion of over 100,000 solar-system-local stars within the complete catalog of stellar bodies in monitors.

Related: Three intruder stars in the Milky Way are “on the run,” or heading in the wrong direction.

The Milky Way exhibits the opposite wrinkling pattern to humans as we age, according to our research. The study team leader at Rensselaer Polytechnic Institute and University of Alabama scientist Thomas Donlon described it in a statement as “a sort of cosmic Benjamin Button, getting less wrinkly over time.”. The last major collision of the Milky Way occurred billions of years later than previously believed, according to research on how these wrinkles fade over time. ****.

It was not until Gaia’s discovery in 2018 that these galactic wrinkles were thoroughly studied to determine the timing of the collision that gave rise to them.

Strange movements of halo stars.

A large number of stars in our galaxy’s halo have unusual orbits; it is thought that these stars are the “leftovers” of galaxies that the Milky Way once ate.

It is thought that many of those stars are remnants of what is known as the “last major merger,” which is the name given to the last major collision between the Milky Way and another galaxy. The Gaia-Sausage-Enceladus (GSE) merger is the name given to the final major collision that scientists believe may have involved a massive dwarf galaxy. One theory holds that it introduced stars on orbits near the Galactic Center into the Milky Way. When the Milky Way was still in its infancy, eight to eleven billion years ago, is when the GSE event is thought to have occurred.

Based on simulations of galactic collisions and mergers, Thomas and his colleagues have been comparing the wrinkling of the Milky Way to actual formation since 2020. The peculiar stellar bodies may have been deposited by a different merger event, according to Gaia observations of these peculiarly orbiting stars, which were made public as part of the space telescope’s Data Release 3 in 2022.

Through these simulated mergers, we can observe how the number and shapes of wrinkles change over time. This allows us to determine the precise moment at which the simulation most closely resembles what we observe in current Gaia data of the Milky Way—a technique we also employed in this new study,” Donlon said. Through this process, we were able to determine that the wrinkles were most likely the result of a dwarf galaxy and Milky Way collision that occurred about 237 billion years ago. This event was given the name Virgo Radial Merger. “.”.

The team’s Heidi Jo Newberg, also from Rensselaer Polytechnic Institute, stated that in order for star wrinkles to be as evident as they are in Gaia data, stars had to join us less than three billion years ago, or at least five billion years later than previously believed. Every time a star swings back and forth through the Milky Way’s center, new wrinkles in the stars form. We wouldn’t be able to distinguish them as distinct features if they had joined us eight billion years ago due to the abundance of wrinkles next to one another. ****.

Reliability of a massive ancient merger in the early history of the Milky Way to explain the peculiar orbits of some stars in the galactic system is called into question by the recent analysis of Gaia’s observations. It also calls into question all the stars that were previously connected to the merger of GSE.

This result, according to Donlon, “is a big change from what astronomers thought up until now,” since a large portion of the Milky Way only joined us within the last few billion years. The expansion of the Milky Way is predicted by many popular models to make head-on collisions with dwarf galaxies of this mass extremely uncommon. ****.

The group also believes that a family of other small dwarf galaxies and star clusters were brought into our galaxy by the Virgo Radial Merger; these would have all been ingested by the Milky Way at roughly the same time.

If any objects previously linked to the GSE event are in fact related to the more recent Virgo Radial Merger, this could be revealed by further research and data from Gaia.

This new study is the most recent in a wealth of findings from Gaia data that are changing the course of the Milky Way’s history.

Due to Gaia’s exceptional capacity to study a large number of stars over Earth, the space telescope has been able to create an unparalleled map of the locations, velocities, and positions of about 1.5 billion stars to date. This has allowed for such cosmic revisionism.

“New data from Gaia is contributing significantly to the ongoing rewriting of the Milky Way’s history,” Donlon stated in closing. Even ten years ago, our understanding of the Milky Way’s past underwent a significant shift, and I believe that understanding of these mergers will continue to change at a rapid pace. “.”.

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