Long period comets come from the Oort Cloud, which sits 30,000 times as far away from the Sun as Earth, and interact with the gravity of the galaxy over time, causing their elongated orbits to bring them closer to the Sun, eventually revealing them as comets once the ice on them starts to sublimate. This is in contrast to solar system objects which travel on elliptical paths and these comets travel on hyperbolic paths, distinguishing them as coming from outside our solar system.