One of these things is not like the others. One of these things does not belong. There’s an interloper lurking in the big dipper. It’s a star with a chemical make-up unlike other stars commonly found in our Milky Way galaxy. In fact, it is much more similar in composition to stars in neighboring dwarf galaxies.
The star J1124+4535 was first identified in 2015 when the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in China found it hanging out in Ursa Major. High resolution images of the invader were captured by the Subaru Telescope in Japan in 2017. The theory is that this strange star originated in a dwarf galaxy that collided with the Milky Way at some point in the deeply distant past, and found itself co-opted by our galaxy when its home galaxy broke apart.
Stars are born from the dust and gases that surround them in their places of birth. So, stars in the same neighborhood usually have the same composition. When stars are made up of different stuff than their neighbors, scientists start looking for their foreign origins.
It is known that the Milky Way as we know it was formed from multiple collisions with, and the absorbing of other galaxies. We’re still on a collision course with the Andromeda Galaxy and the Large Magellanic Cloud before that. According to the study, “analysis of J1124+4535 provides “the clearest chemical signature” yet of the ancient galaxy mergers that shaped the Milky Way billions of years ago.”