The sun is a 'runaway world collector' that can trap passing rogue planets 

 The sun could collect rogue planets and hold them at the outskirts of the solar system for millions of years, occasionally trading them with neighboring star Alpha Centauri. 

https://cdn.mos.cms.futurecdn.net/GKNhAKierrB9ZGQWpvdFy7.png

https://www.space.com/runaway-world-collector-rogue-planets