The correct answer is option 3: rapidly spinning stars. Pulsars are a type of neutron star, which is formed when a massive star undergoes a supernova explosion and collapses under its own gravity. Pulsars have an incredibly strong magnetic field and rotate rapidly, emitting beams of electromagnetic radiation along their magnetic axes. These beams can be observed as regular pulses of radiation, hence the name "pulsar." However, it is important to note that pulsars can have a variety of rotational periods, ranging from milliseconds to several seconds. Option 1 and option 2 are incorrect because pulsars can be moving towards or away from Earth or have no significant motion at all. Option 4 is also incorrect, as the temperature of a pulsar can vary but is generally not considered "high" compared to other stellar objects.