The Milky Way, a vast spiral galaxy housing billions of stars, including our sun, has undergone a complex journey to reach its current size, as indicated by recent research highlighting a significant event early in its existence.
Scientists examining clusters of stars near the center of the Milky Way have uncovered proof that our galaxy engulfed a smaller galaxy around 11.8 billion years ago, when the universe was less than 15% of its current age. This marks the earliest-known galactic merger for the Milky Way, demonstrating its growth through not only internal star formation but also by merging with smaller galaxies within its gravitational reach.
The smaller galaxy, classified as a dwarf galaxy, was estimated to contain stars with a mass equivalent to 500 million times that of the sun at the time of the merger, about a quarter of the Milky Way’s size at that time.
Researchers utilized the Hubble and Gaia telescopes to study stellar clusters within the innermost 20,000 light-years of the Milky Way, analyzing their age, chemical composition, and trajectory. A light-year represents the distance light travels in a year, equivalent to 9.5 trillion kilometers.
These stars joined the Milky Way following a galactic merger approximately two billion years after the Big Bang, originating from a dwarf galaxy named Low-energy-Kraken-Heracles (LKH), which had been studied in previous research.
Astrophysicist Davide Massari, the lead author of the study published in the journal Nature Astronomy, stated, “The primary discovery of our research is the clear identification of the first merger event experienced by our galaxy during its early stage.”
‘Peaceful’ Galactic Merger
The debate over whether the Milky Way’s early growth was driven by internal star formation or galactic mergers has been ongoing. The new study suggests that the merger introduced a significant number of stars and interstellar gas to the Milky Way early on, supporting star formation and the presence of dark matter.
-
Astronomers reveal first photograph of a monster black hole at the heart of our galaxy
-
Milky Way was part of cosmic collision 10 billion years ago
Massari explained, “I would describe the merger as relatively peaceful in terms of stars, with no star-to-star collisions. However, the gas collision was more ‘explosive,’ likely leading to the formation of numerous stars.”