Milky Way’s Recent Galactic Merger Challenges Previous Astronomical Theories

Recent findings from the Gaia space telescope suggest that the Milky Way might have absorbed a small galaxy relatively recently in cosmic terms. This latest major collision appears to have occurred much later than previously believed.

The Milky Way is known to have expanded through numerous violent mergers, where smaller galaxies are torn apart by the massive gravitational forces of our galactic home. These events scatter stars from the consumed galaxy throughout the Milky Way’s halo and its iconic spiral arms, creating “wrinkles” that ripple through our galaxy, affecting various star “families” differently.

Today We Found Out That the Gaia space telescope reveals the Milky Way's history of cosmic cannibalism! Dive into the galactic drama. Read more: https://t.co/8aOfJmJv9t

— What We Found Out (@WhatWeFoundOut) June 10, 2024

Gaia, which accurately tracks the position and movement of over 100,000 stars near our solar system among a broader catalog, uses these measurements to rewrite the Milky Way’s history by studying these wrinkles. Thomas Donlon, the lead researcher from Rensselaer Polytechnic Institute and the University of Alabama, noted, “We get wrinklier as we age, but for the Milky Way, it’s the opposite. It’s getting smoother over time. By observing how these wrinkles fade, we can pinpoint the last significant collision, which occurred billions of years later than we previously thought.”

These galactic wrinkles, first discovered by Gaia in 2018, have now been extensively studied to determine the timing of the collision that caused them. The galaxy’s halo, filled with stars in unusual orbits, holds remnants from galaxies once consumed by the Milky Way. Many of these stars are believed to be from a massive collision involving a dwarf galaxy, known as the Gaia-Sausage-Enceladus (GSE) merger, estimated to have occurred between eight and 11 billion years ago.

Since 2020, Donlon’s team has compared the Milky Way’s wrinkles to simulations of galactic collisions, using the latest data from Gaia to refine their understanding of these events. They concluded that a dwarf galaxy merger, named the Virgo Radial Merger, likely occurred about 2.7 billion years ago. Heidi Jo Newberg, a team member from Rensselaer, explained, “The clarity of the wrinkles in the Gaia data indicates they formed less than three billion years ago, which is at least five billion years later than previously estimated. New wrinkles form as stars oscillate through the Milky Way’s center, and if they had joined us earlier, the wrinkles would blend together, making them indistinguishable.”

This revelation challenges the necessity of a massive, ancient merger in the early history of the Milky Way to explain some stars’ strange orbits and questions the association of all stars previously linked to the GSE event. Donlon added, “This finding—that a large portion of the Milky Wayout only joined recently—is a significant shift from earlier astronomical theories, which did not anticipate such a recent, major merger.”

The team also believes that the Virgo Radial Merger brought other small dwarf galaxies and star clusters into the Milky Way, which were also assimilated around the same time. Further analysis and future Gaia data could determine if any objects previously tied to the GSE event are actually linked to this more recent merger. This ongoing research is part of a series of discoveries from Gaia data that continue to revise the understanding of the Milky Way’s history. Donlon concluded, “Our view of the Milky Way’s past has dramatically changed in just the last decade, and I believe our understanding of these mergers will keep evolving quickly.”

Major Points

• Recent data from the Gaia space telescope suggests the Milky Way absorbed a small galaxy around 2.7 billion years ago, significantly later than previously thought.
• This merger, known as the Virgo Radial Merger, indicates the Milky Way continues to smooth out “wrinkles” created by galactic collisions.
• Findings challenge the notion that all strange star orbits in the Milky Way are remnants of an ancient, massive merger occurring over 8 billion years ago.
• The Gaia telescope’s detailed tracking of stars has allowed researchers to refine the timeline of these galactic events, suggesting a major revision of our galaxy’s history.
• Ongoing research and future Gaia data are expected to further alter our understanding of the Milky Way’s past and the dynamics of its mergers.

Lap Fu Ip – Reprinted with permission of Whatfinger News