Astronomers have discovered a star in the Milky Way that doesn’t belong. Officially known as J1124+4535, the star has a chemical composition unlike any others ever observed in our home galaxy, suggesting it’s an intergalactic interloper that may have come from a dwarf galaxy that was swallowed up by the Milky Way.

The star in question first came to the attention of astronomers through a survey conducted by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Located in China, the telescope can help astronomers figure out the chemical compositions of stars by analyzing the spectrum of their light.

Through LAMOST observations and a follow-up using the Subaru Telescope in Japan, J1124 was found to have a relatively low amount of magnesium and high levels of europium. This particular chemical composition so far seems to be unique to this star, compared to the rest of the Milky Way.

The star J1124-4535 was found to have an unusual chemical composition, indicating it originated in a...

That said, other stars have been found with this kind of composition before – just not around here. In fact, they’re relatively common in dwarf galaxies, where star formation happens slower than it does in larger galaxies like the Milky Way, seeding stars with different amounts of different chemicals. That suggests that J1124 formed in a dwarf galaxy that was later absorbed by our own.

This kind of galactic merger happens all the time. The aftermaths of collisions between the Milky Way and smaller galaxies are visible all around us, and many more are predicted in the future – culminating in a spectacular merger between the Milky Way and Andromeda in about four billion years’ time.

J1124+4535 isn’t the first intergalactic star to be discovered in our neck of the woods. Stars traveling at hypervelocity speeds have been found to be hurtling towards the Milky Way from other galaxies, with the Large Magellanic Cloud, a dwarf galaxy that orbits our own, the most likely point of origin.

The research was published in the journal Nature Astronomy.

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