Around a quarter of the star clusters in our galaxy sneaked their way in from other galaxies, according to scientists from Swinburne University of Technology in Australia.
"It turns out that many of the stars and globular star clusters we see when we look into the night sky are not natives, but aliens from other galaxies," said Swinburne astronomer Professor Duncan Forbes.“They have made their way into our galaxy over the last few billion years."
The finding, which confirms previous suspicions, was made using Hubble Space Telescope data to compile the largest ever high-quality database of the age and chemical properties of each of these clusters.
"We determined that these foreign-born globular star clusters actually make up about one quarter of our Milky Way globular star cluster system," says Forbes. "That implies tens of millions of accreted stars – those that have joined and grown our galaxy – from globular star clusters alone."
The researchers’ work also suggests that the Milky Way may have swallowed up more dwarf galaxies than was previously thought.
"We found that many of the foreign clusters originally existed within dwarf galaxies - that is 'mini' galaxies of up to 100 million stars that sit within our larger Milky Way," said Forbes.
"Our work shows that there are more of these accreted dwarf galaxies in our Milky Way than was thought. Astronomers had been able to confirm the existence of two accreted dwarf galaxies in our Milky Way – but our research suggests that there might be as many as six yet to be discovered."