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How can passing stars or interstellar clouds send Oort cloud objects toward the Sun?

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asteroid Ida and its satellite, Dactyl — Small body Asteroid Ida and its satellite, Dactyl, photographed by the Galileo spacecraft on August 28, 1993, from a distance of about 10,870 km (6,750 miles). Ida is about 56 km (35 miles) long and shows the irregular shape and impact craters characteristic of many asteroids. The Galileo image revealed that Ida is accompanied by a tiny companion about 1.5 km (1 mile) wide, the first proof that some asteroids have natural satellites.

The Oort cloud is a vast, spherical reservoir of icy small bodies located at extreme distances from the Sun, typically between 20,000 and 50,000 astronomical units (AU). Because these objects are so far away, their orbits are only loosely bound to the Sun, making them highly susceptible to external gravitational influences.12

Passing stars or giant interstellar molecular clouds can exert gravitational forces that perturb the orbits of these icy bodies. These gravitational tugs can alter the objects' trajectories, effectively "nudging" them out of their distant, stable orbits and sending them inward toward the inner [solar system]. Once these objects are directed toward the inner planetary region, they may be observed as "new" long-period comets.123

In addition to stellar and interstellar encounters, the gravitational forces known as disk tides—exerted by the mass of the Milky Way Galaxy’s disk—also play a critical role in disrupting these orbits and maintaining a steady flux of comets into the visible region.12