Milky Way may have swallowed another galaxy shortly after the Big Bang
Astronomers have found new evidence that the Milky Way experienced a major galactic merger in the early universe, possibly just a few billion years after the Big Bang. The discovery adds another important chapter to the long and violent history of our home galaxy.
The Milky Way may look calm from Earth, but its past was anything but peaceful. Like many large galaxies, it grew over time by pulling in smaller galaxies and absorbing their stars, gas, and dark matter. These ancient collisions helped shape the Milky Way’s structure, chemistry, and stellar population as we see them today.
To investigate this hidden history, researchers used the Hubble Space Telescope to study 39 globular clusters orbiting within the Milky Way. Globular clusters are dense collections of hundreds of thousands of old stars, and they act like cosmic fossils. Because they preserve clues about the conditions in which they formed, scientists can use them to trace events that happened billions of years ago.
By combining Hubble’s detailed observations with data from the Gaia space observatory, astronomers were able to measure the ages and chemical compositions of these clusters with remarkable precision. This allowed them to identify a distinct group of globular clusters that appear different from the rest, suggesting they did not originally form inside the Milky Way.
The evidence points to an ancient galaxy known as Low-energy-Kraken-Heracles. Researchers estimate that this long-lost galaxy had a stellar mass around 500 million times greater than the Sun. According to the study, it likely merged with the young Milky Way about 12.3 billion years ago.
That timing is especially significant. The universe itself is about 13.8 billion years old, meaning this merger may have happened when the cosmos was still relatively young. At that stage, the Milky Way was smaller, more chaotic, and still in the process of building the structure that would eventually become the galaxy we live in today.
Galaxy mergers are common throughout the universe, especially in the early stages of cosmic evolution. The Milky Way has experienced several such events, including a well-known collision with the Gaia-Sausage-Enceladus galaxy roughly 10 billion years ago. That merger had a major impact on the Milky Way’s shape and helped create parts of its stellar halo.
The newly identified Low-energy-Kraken-Heracles event may have occurred even earlier, making it one of the most ancient mergers ever traced in our galaxy’s history. If confirmed, it could help astronomers better understand how the Milky Way assembled its earliest stars and how large spiral galaxies grow over billions of years.
This discovery also shows how powerful globular clusters can be as tools for galactic archaeology. By studying their movements, ages, and metal content, scientists can reconstruct events that happened long before the Sun and Earth existed.
The Milky Way is still evolving today, and future mergers are expected. In several billion years, it is predicted to collide with the Andromeda Galaxy, creating a new, larger galaxy. For now, studies like this reveal that our galaxy’s past was filled with dramatic encounters that helped turn it into the vast spiral system we see in the night sky.
