Galaxies & Cosmic Structures
Quasars
Quasars are the extremely luminous centers of distant galaxies, powered by supermassive black holes feeding on gas.
Their light can outshine all the stars of their host galaxy, letting us see them across most of cosmic history.
- Observe
A star-like point of light, extremely luminous, at great distance.
- Measure
Redshift shows distance; spectra show gas motions.
- Model
Accretion onto a supermassive black hole releases enormous energy.
- Explain
A black hole feeding on gas can outshine a galaxy.
What is it?
A quasar is a type of active galactic nucleus: a supermassive black hole surrounded by a hot accretion disk of gas. The disk radiates so intensely, from radio to X-rays, that a quasar can outshine the rest of its host galaxy.
Quasars were identified in the early 1960s. The first to have its distance measured was 3C 273 in 1963. Some quasars are seen as they were when the universe was less than a billion years old, which raises the question of how such massive black holes grew so quickly.
How does it happen?
- Stage 1Gas falls toward a supermassive black hole
- Stage 2Accretion disk heats up
- Stage 3Intense radiation and sometimes jets
- Stage 4Quasar shines across the universe
What do we actually observe?
- Brightness
- Some quasars are hundreds of times as luminous as the Milky Way.
- Redshift
- Their light is stretched by cosmic expansion, so distance can be read from the spectrum.
- Variability
- Brightness changes over days to years, which limits the size of the emitting region.
How do scientists detect it?
- Sky surveys. The Sloan Digital Sky Survey and DESI have cataloged large numbers of quasars.
- Multi-wavelength telescopes. Radio, X-ray and optical data together reveal the disk, jets and surroundings.
Why does it matter?
- They trace the growth of black holes across cosmic time.
- Their light passes through intergalactic gas, so absorption lines map that gas.
- Lensed quasars can be used to measure the expansion rate.
The SpaceWeatherTracker connection
Jets from quasars are magnetized plasma outflows, an extreme cousin of the eruptions and winds SpaceWeatherTracker follows from the Sun.
This is an explainer. SpaceWeatherTracker does not show live data for this phenomenon; see the “Space Phenomena Now” section on the hub for what is currently monitored.
Related phenomena
Primary family: Galaxies & Cosmic Structures
Quasars: common questions
What is a quasar?
The very luminous core of a distant galaxy, powered by a supermassive black hole pulling in gas.
Are quasars still forming?
Quasars are more common in the distant, early universe. Nearby galaxies have active nuclei, but true quasars are rare now.