Answer:
which is not a required force.
Explanation:
An adjective clause is a group of words with at least a verb and a subject that does not express a complete thought (they're dependent clauses) and whose function is to modify nouns. Very often, these type of clauses begin with a relative pronoun (who, whom, whose, that, which) or a relative adverb (when, where, why).
In the sentence, "which is not a required force" is an adjective clause because it is a dependent clause (it does not express a complete thought on its own), it modifies or describes the noun "astronomy" and it begins with the relative pronoun "which."
