[pbhjpbhj]

Considering a point particle, what constrains it from orbiting [which is what I'm assuming we're meaning here as all matter has to move radially to cross the event horizon]? If it had a tangential component to its momentum prior to meeting the event horizon (EH) wouldn't it continue to orbit past the EH?

[pa7x1]

Nothing forbids a slight tangential component but the movement of the test particle is inevitably decreasing in r.

Closed orbits are impossible though, all test particles finish at the singularity in a finite amount of proper time.

[entropicdrifter]

I think by definition the event horizon can only be crossed in one direction (towards the center). By this I mean nothing escapes once it is past that point. It's defined by being the point of no return

It is the point at which nothing, no matter how fast or massive, can possibly return from the gravitational pull. For instance: light, traveling at the speed of light in a vacuum, cannot escape once it has crossed the event horizon; it's pulled inevitably inward.

[a1369209993]

> what constrains it from orbiting

Not quite what you seem to be asking, but the event horizon is the point where[0] the escape velocity is equal to the speed of light; the orbital velocity at that distance is greater (by a factor of ln 2 IIRC, so v_orbital ≈ 1.44c). There's a more distant distance, called the innermost stable orbit or the photon sphere, where the orbital velocity is equal to c (so photons will orbit if you emit them tangentially at this height), but the escape velocity is only ~0.69c.

0: It's not quite right to say that that's because the escape velocity is equal to c, though.