Quasars, or quasi-stellar objects, are among the most distant (and oldest) know objects in the universe. The were initially discovered by radio telescopes as strong emitters of RF radiation. Astronomers then viewed them with powerful telescopes and found that they also appeared as small fuzzy discs of visible light. Actually their apparent small size is an illusion based on their being extremely distant from us. Spectrographic analysis showed extreme red shifts, proving that the light from quasars was emitted many billions of years ago and that actually quasars are galaxy-like objects with black holes in their centers formed in the early stages of the universe.
Pulsars are neutron stars, left after the collapse of massive and highly energetic stars, named for rapidly pulsing radio emissions.
Pulsars are rapidly spinning neutron stars which appear to pulse.
Quasars are the brightest objects in our universe but they are not stars.
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