Answer:
Several teams observed the predicted sharp edges characteristic of a cosmic string.
Step-by-step explanation:
Active voice is when the subject is followed by the verb and then the object. Whereas, in a passive voice, the object assumes the starting point, folllowed by the verb and then the subject.
The sentence - The predicted sharp edges characteristic of a cosmic string were observed by several teams
is written in the passive voice. So, to change it into the active voice, the subject "several teams" will begin the sentence, followed by the verb "observed" and then the object.
Thus, the final sentence in the active voice will become
Several teams observed the predicted sharp edges characteristic of a cosmic string.