The Milky Way may have merged with another galaxy shortly after the Big Bang

Studying the Milky Way is a difficult task for astronomers. Indeed, as they look farther back in time, it becomes more difficult to determine what happened. But thanks to the Hubble Space Telescope, scientists have managed to uncover a surprising fact about our galaxy.

We know that when it was younger, it was smaller, and its size was comparable to that of young galaxies in the universe. But its behavior was also more chaotic, and mergers with other galaxies also took place.

Thus, to study this tumultuous past, astronomers have used Hubble to observe 39 globular clusters in the Milky Way. These clusters contain hundreds of thousands of stars and may have different origins. In other words, these clusters are thought to have originated from other structures that merged with our galaxy, as explained by Chiara Zerbinati, a co-author of the study at the University of Bologna in Italy: 

"Thanks to the high resolution and depth of Hubble imaging, we could measure the age and the metal content of these clusters with unprecedented precision. Coupled with measurements from Gaia, this made it possible to distinguish a population of globular clusters that are different from the others."

According to the results, these clusters originated from a galaxy called Low-energy-Kraken-Heracles. It had a stellar mass of about 500 million times that of the Sun. And that’s not all, because scientists believe this merger took place about 12.3 billion years ago.

But galaxy mergers are not rare events in the universe. Indeed, the Milky Way has already merged with other galaxies, notably Gaia-Sausage-Enceladus 10 billion years ago, which altered its shape and structure.