(CNN) Scientists In the last few years have studied the first observed interstellar visitors to our solar system. They include a comet called 2I/Borisov, spotted in 2019 and still passing through, and an asteroid called 'Oumuamua that zipped through quickly in 2017.

Now, astronomers have identified a more permanent outsider presence in our solar system. It's a group of interstellar asteroids that checked in a long time ago and never left. And they've been hiding in plain sight for billions of years, according to a new study published this week in the Monthly Notices of the Royal Astronomical Society.

These asteroids were likely around when our solar system was forming 4.5 billion years ago. They originated in a different star system. And when our solar system was forming, it was likely closer to other baby star systems as well.

The European Southern Observatory captured this image of the Lobster Nebula, where gas and dust surround young, forming stars. Stars are closer together in nebulae, meaning they can capture objects from each other.

"The close proximity of the stars meant that they felt each others' gravity much more strongly in those early days than they do today," said Fathi Namouni, researcher at the Observatoire de la Côte d'Azur and lead study author, in a statement. "This enabled asteroids to be pulled from one star system to another."

Namouni and fellow researcher Maria Helena Moreira Morais at the Universidade Estadual Paulista in Brazil used numerical modeling to simulate the infancy of our solar system and pinpoint the location of the asteroids billions of years ago.

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