Working definition
An active galactic nucleus is a compact, unusually luminous galactic center powered by matter interacting with a central supermassive black hole. Its observed class depends on accretion state, obscuring material, jets, host environment, variability, wavelength, and viewing angle.
What is measured
- Compact nuclear emission is measured across radio to gamma-ray bands.
- Spectral lines, polarization, and variability constrain emitting regions.
- High-resolution imaging separates nucleus, jets, and host where possible.
What is inferred
- Accretion rate and black-hole mass are estimated under physical and scaling models.
- Unified models connect some observed classes through orientation and obscuration.
- Feedback is inferred from jets, winds, gas kinematics, and host properties.
Fact-layer dependency
The explanatory layer cannot rewrite these fields.
time.utcInstantsubject.identifiersreference.framecoordinates.valuescoordinates.uncertaintyprovenance.providerWhat is observed
Compact nuclear emission is measured across radio to gamma-ray bands. Spectral lines, polarization, and variability constrain emitting regions. High-resolution imaging separates nucleus, jets, and host where possible.
Active galaxies exhibit luminous central emission and may show accretion-disk, obscuration, and jet signatures across multiple wavelengths.
Boundary: Nuclear brightness is not the combined stellar luminosity.
How inference enters
Accretion rate and black-hole mass are estimated under physical and scaling models. Unified models connect some observed classes through orientation and obscuration. Feedback is inferred from jets, winds, gas kinematics, and host properties.
Limits and unresolved questions
Nuclear brightness is not the combined stellar luminosity. Mass estimates can be method dependent. Correlation with host properties does not alone establish feedback causality.
Different geometries and accretion states can produce overlapping observational classifications.
Boundary: Correlation with host properties does not alone establish feedback causality.
Sources
Each source states both what it establishes and where its authority ends. Access dates record the last public verification.
- [1]Galaxies · NASA Science · accessed 2026-08-15
Establishes: Galaxies as gravitationally associated systems of stars, gas, dust, and dark matter, with observed morphological and environmental diversity.
Boundary: Morphological class is descriptive and viewing-angle dependent; it does not by itself determine formation history or central activity.
- [2]Black Holes · NASA Science · accessed 2026-08-15
Establishes: Black-hole observational signatures through surrounding emission, orbital dynamics, lensing, and gravitational waves.
Boundary: Black holes are inferred through measurable effects and relativistic models; an illustration of an event horizon is not a direct optical image of the horizon.
- [3]Tour of the Electromagnetic Spectrum · NASA Science · accessed 2026-08-15
Establishes: The wavelength and frequency domains of electromagnetic radiation and why different observing bands require different detectors and reveal different processes.
Boundary: A wavelength band does not uniquely identify a physical source; interpretation also depends on calibration, spectral shape, environment, and competing mechanisms.