Doppler beaming

Doppler beaming is the apparent brightening and directional concentration of radiation from a source moving relativistically toward an observer, caused by relativistic transformations of frequency, arrival rate, and emission angle.

Relativistic Doppler effect: The change in observed frequency caused by relative motion when special relativity governs the transformation. The approaching source’s frequency shift contributes to its enhanced observed brightness.
Relativistic jet: A narrow outflow of plasma launched at relativistic speed from an energetic astronomical object. Jets directed near the line of sight can have their radiation strongly amplified.
Relativistic Doppler boosting: The increase or decrease in observed flux caused by relativistic motion toward or away from an observer. It emphasizes the flux amplification aspect, while beaming also includes directional concentration.
Relativistic beaming bias: The observational selection effect favoring detection of relativistically moving sources aimed toward the observer. Aligned sources appear disproportionately bright, skewing observed samples.
Relativistic aberration: The relativistic change in the observed direction of light when transforming between inertial frames. It concentrates radiation emitted across many directions into a forward cone.
Blazar: An active galactic nucleus whose relativistic jet points close to the observer’s line of sight. Its extreme apparent luminosity and rapid variability are signatures of strong beaming.
Inverse-square law: A relation in which the intensity from a point source decreases as the square of distance. Distance changes received flux without producing the directional enhancement caused by motion.
Orientation-based unification: An account of apparent differences among active galactic nuclei as consequences of viewing angle and obscuration. Beaming makes orientation a major determinant of how an active nucleus appears.
Lorentz transformation: The equations relating space and time coordinates between inertial frames in special relativity. It supplies the frame transformations behind the frequency and angular changes.
Active galactic nucleus: A galaxy’s central region powered by accretion onto a supermassive black hole. Relativistic beaming shapes the observed emission of its jet-producing subclasses.

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