What characterizes a pulsar?

A pulsar is characterized by its consistent and regular emission of electromagnetic radiation, usually observed as pulses of radio waves. This phenomenon occurs because pulsars are highly magnetized, rotating neutron stars, which emit beams of radiation from their magnetic poles. As the star rotates, the beams sweep across space like a lighthouse beam. If these beams are aligned with Earth, they are perceived as pulses, hence the name "pulsar."

The key aspect of pulsars is the regularity of their pulse emissions; the rotation period can range from milliseconds to a few seconds, and some pulsars are known for their extremely precise timing, which can rival atomic clocks. This periodicity is what sets pulsars apart from other types of stars and variable stars, which may change brightness in a more unpredictable manner.

In this context, other options describe different celestial phenomena. A rapidly spinning black hole is not accurate, as black holes do not emit radiation in a pulsating pattern and do not fulfill the definition of a pulsar. Variable stars differ from pulsars as they exhibit changes in brightness that are not always regular or periodic. A nebula represents a different type of astronomical object entirely, typically a cloud of gas and dust, rather than a star that emits consistent pulses