Question

a periodic astrophysical radio source is detected that has a period of 1.557 milliseconds. what is the cause of this signal? a massive black hole at the center of a galaxy a rapidly rotating neutron star an extraterrestrial civilization a rapidly rotating red giant star

Explanation:

Pulsars, which are rapidly rotating neutron stars, emit periodic radio - signals with short periods. The period given (1.557 milliseconds) is characteristic of a pulsar. Black holes do not emit such periodic radio - signals in this way. Extraterrestrial civilizations have not been confirmed to be the source of such common periodic signals, and red giant stars do not rotate fast enough to produce such short - period signals.

Answer:

a rapidly rotating neutron star