An adverb is a word or an expression that is used in English Grammar that modifies a verb, an adjective, a determiner, a clause, a sentence or a preposition also.
It adds a quality to all these expressing their relation with time, place, circumstance, cause, degree or the manner. They are intensifiers and they even come in the form of an adverb phrase.
The gerund phrase in this sentence would be "becoming a movie star" because of the verb "becoming" which acts as somewhat of an introduction to the rest of the phrase.
