The Milky Way galaxy, a vast spiral structure housing billions of stars, including our sun, has undergone a complex evolutionary journey, as indicated by recent research highlighting a significant event in its early history.
A team of scientists studying star clusters near the center of the Milky Way has uncovered evidence suggesting that approximately 11.8 billion years ago, our galaxy merged with a smaller galaxy. This merger, occurring when the universe was in its early stages, marks the earliest known galactic collision involving the Milky Way, demonstrating its growth through both internal star formation and absorption of smaller galaxies within its gravitational grasp.
The smaller galaxy involved in the merger was classified as a dwarf galaxy, distinguishing it from larger galactic structures like the Milky Way. Researchers estimate that this dwarf galaxy contained stars with a mass equivalent to 500 million times that of the sun at the time of the merger, representing roughly a quarter of the Milky Way’s size during that era.
Utilizing data from the Hubble and Gaia telescopes, researchers analyzed stellar clusters within the innermost 20,000 light-years of the Milky Way, examining their age, chemical composition, and trajectories. One light-year is equivalent to the distance light travels in a year, approximately 9.5 trillion kilometers.
These stars became integrated into the Milky Way following the galactic merger, which occurred around two billion years after the Big Bang. The dwarf galaxy where these stars originated was named Low-energy-Kraken-Heracles (LKH), reflecting prior studies exploring the possibility of such a merger.
Lead author Davide Massari, an astrophysicist from the National Institute for Astrophysics in Bologna, Italy, emphasized the significance of their findings, describing the merger as a pivotal event in the early development of the Milky Way.
The study sheds light on the ongoing debate regarding the Milky Way’s growth mechanism. Massari noted that the merger introduced a substantial volume of stars, interstellar gas, and dark matter into the Milky Way, fueling star formation in its early history.
While the merger was relatively peaceful in terms of star interactions, it triggered an ‘explosive’ collision of gas that likely stimulated the formation of numerous stars. The integration of stars from the dwarf galaxy into the Milky Way, although challenging to pinpoint due to interstellar dust, remains a crucial aspect of the galaxy’s evolutionary history.
The Milky Way has also been involved in two other major galactic mergers. It assimilated the Gaia-Sausage-Enceladus dwarf galaxy roughly 1.8 billion years after the LKH merger, followed by a merger with the Sagittarius dwarf galaxy over the last six billion years.
Massari emphasized that each merger has influenced the formation of our solar system and Earth itself. By reconstructing the Milky Way’s past, researchers aim to unravel the fundamental question of our cosmic origins.