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Quasar and AGN
A galaxy whose central black hole is feeding so hard it outshines everything around it.
An active galactic nucleus is a supermassive black hole with an accretion disc bright enough to compete with the entire galaxy; a quasar is the extreme end of that, visible across most of the observable universe. They were mistaken for stars when first catalogued — hence quasi-stellar — until their redshifts revealed the distances. Because they are so bright and so distant they double as backlights, and the absorption lines imprinted on their spectra map the intervening gas.
Where it has come up lately
Universe Today
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Universe Today
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Related terms
Event horizon
The boundary around a black hole past which nothing gets out — not a surface, but a point of no return.
Accretion disc
The flat, ferociously hot spiral of matter falling onto a compact object.
Singularity
The point where our description of gravity stops producing meaningful answers.
Schwarzschild radius
How small you would have to squeeze something to make it a black hole.
Questions
What is Quasar and AGN?
A galaxy whose central black hole is feeding so hard it outshines everything around it.
Why does it matter?
They were mistaken for stars when first catalogued — hence quasi-stellar — until their redshifts revealed the distances. Because they are so bright and so distant they double as backlights, and the absorption lines imprinted on their spectra map the intervening gas.