A quasar is the extremely luminous core of a distant galaxy, powered by matter falling into a supermassive black hole — among the brightest objects in the universe. A pulsar is the collapsed remnant of a single star: a rapidly spinning neutron star whose beam sweeps past us in regular pulses. Galactic scale versus stellar scale.
The core difference
Both were discovered in the 1960s by radio astronomy and both have odd names. They are entirely different objects.
- quasar — "quasi-stellar radio source". A galaxy's active core, powered by a supermassive black hole. Enormously distant and bright.
- pulsar — "pulsating star". A spinning neutron star, the remnant of a supernova, emitting a beam that sweeps past us regularly.
Why both got confusing names
Each looked star-like at first. Quasars appeared as point sources that resembled stars but sat at impossible distances — hence "quasi-stellar". Pulsars produced pulses so regular that the first was informally labelled LGM-1, for "little green men", before a natural explanation was established.
Scale
A pulsar is roughly the size of a city with more mass than the Sun. A quasar can outshine its entire host galaxy. They are not comparable objects in any respect but their discovery era.
Frequently asked questions
What powers a quasar?
Matter falling into a supermassive black hole at a galaxy's centre, releasing enormous energy as it heats.
What makes a pulsar pulse?
It spins rapidly and emits a beam that sweeps past us like a lighthouse, producing regular pulses.
Why is it called a quasar?
From "quasi-stellar radio source" — it looked like a star but could not be one, given its distance.