Astronomers have found evidence that the Milky Way absorbed a smaller galaxy roughly 11.8 billion years ago, according to a report from Reuters. The finding sheds new light on how our galaxy grew during its formative years.
The research, published in the journal Nature, points to a massive collision event that occurred about 1.8 billion years before a previously known merger called Gaia-Sausage-Enceladus. That earlier clash, scientists say, was a major step in building the Milky Way into the large galaxy we see today.
The discovery came from studying stars that appear to have originated in another galaxy. According to The Conversation, galactic archaeologists identified these stars as foreign to the Milky Way, tracing their origins back roughly 12 billion years. The work also involved data from the Hubble Space Telescope, which helped solve a long-standing mystery about a merger in the galaxy's early years.
Reuters reports that the findings highlight two giant collisions in the Milky Way's past. The first, now dated to about 11.8 billion years ago, was followed by the Gaia-Sausage-Enceladus event. Together, these clashes helped shape the galaxy's structure and stellar population.
The study adds to a growing picture of the Milky Way as a galaxy built through repeated mergers with smaller neighbors. By pinpointing the timing of these events, researchers can better understand how galaxies evolve over cosmic time.
What to watch next: astronomers will likely look for more ancient merger signatures in star data, which could reveal even earlier collisions in the Milky Way's history.
