Where are the articles?

Solution 1:

"Into orbit"

There are many possible orbits around an astronomical body, so "the orbit" is incorrect unless you have already specified which orbit you are talking about. "An orbit" would be grammatically correct, but "In orbit" has become idiomatic to describe being in a state of orbiting around something and so is often used.

"Part of" is also idiomatic where "part" is used like "some of" or "all of". "A part of" is also grammatically correct.

"The accretion disk" would be used only if it had been mentioned before ( or if only one could exist in the circumstances and it was universally understood to exist).