The correct answer is Ferraro and Newman.
However, you should put the two names behind commas to make it an appositive since it's the key ingredient to making an appositive phrase. Astronomers, Ferraro and Newman, study the speed of stars circling the galactic center of the galaxy. It is an appositive because it describes the astronomers more but is not necessary and could be removed without affecting the truth value of the sentence.
