There are plenty of rogue stars outside galaxies, but we have never seen a rogue star with a planetary system. Can an intergalactic planetary system exist?
First of all, a star and its planetary system need a galaxy to form. There needs to be enough existing matter to collapse into the star. And there’s just nothing in a big void like that.
It’s kinda like the process of making a snowman: You take a small ball of snow and roll it over loose snow on the ground. The loose snow will get incorporated into the ball and the ball gets bigger.
A star is just a ball of space dust so big that nuclear fusion stars. Our own solar system came as a result of a supernova explosion.
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However, stars can be ejected from galaxies and start floating in deep space, but in order for that to happen, you would need something quite violent happening.
Stars, for example, can be ejected by the chaos of galaxy mergers.
But if a star gets flung off into intergalactic space and it happens that the star had planets orbiting around, the planets would be ripped off and held somewhere entirely different but nowhere near the original star. And as you know, life as we know it wouldn’t have a chance to exist on a planet without a star.
So, there’s no such thing as an intergalactic planetary system out there – at least as far as we know!