An infrared excess is a measurement of an astronomical source, typically a

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

, that in their

spectral energy distribution A spectral energy distribution (SED) is a plot of energy versus frequency or wavelength of light (not to be confused with a 'spectrum' of flux density vs frequency or wavelength). It is used in many branches of astronomy to characterize astron ...

has a greater measured

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ...

than expected by assuming the star is a blackbody radiator. Infrared excesses are often the result of

circumstellar dust Circumstellar dust is cosmic dust around a star. It can be in the form of a spherical shell or a disc, e.g. an accretion disk. Circumstellar dust can be responsible for significant extinction and is usually the source of an infrared excess for s ...

heated by starlight and reemitted at longer wavelengths. They are common in

young stellar object Young stellar object (YSO) denotes a star in its early stage of evolution. This class consists of two groups of objects: protostars and pre-main-sequence stars. Classification by spectral energy distribution A star forms by accumulation of mat ...

s and evolved stars on the

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

or older. In addition, monitoring for infrared excess emission from stellar systems is one possible method that could enable a search for large-scale stellar engineering projects of a hypothetical extraterrestrial civilization; for example a Dyson sphere or

Dyson swarm A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its solar power output. The concept is a thought experiment that attempts to explain how a spacefaring civilization would mee ...

. This infrared excess would be the outcome of the waste heat emitted by the aforementioned structures if they are considered blackbodies at temperatures close to 300 K.

References

Observational astronomy {{astronomy-stub