Astrophysics (Index)About

black-body radiation

(EMR due to the temperature of a body with a characteristic spectrum)

Black-body radiation is a kind of thermal radiation (aka thermal emission, electromagnetic radiation (EMR) from a body due to its heat), specifically that from a body that is in thermodynamic equilibrium, which implies a constant, uniform temperature. It is a continuum emission, i.e., producing continuous spectrum, with a specific shaped spectral energy distribution (SED), dependent only on the temperature of the body (a black-body spectrum). The SED is "hill-shaped", its peak at a wavelength calculable from the temperature by Wien's displacement law. Planck's law (Planck function) describes the whole spectrum:

I(ν,T) = 2hν3/c2 × 1/(ehν/(kT)-1)

The black-body spectrum represents an ideal case, given that thermodynamic equilibrium and uniform temperature is never perfect, but all materials produce radiation associated with their temperature. The ideal case and its equation represent a useful first approximation, e.g., for stars' spectra.

The terms Planckian and non-Planckian (NP) are used to describe an EMR source (or its spectrum) as adhering to the black-body spectrum or not. Thermal radiation from optically thin plasma diverges a bit from the black-body spectrum.

Given the temperature-dependent black-body spectrum with its hill and peak, particular bands have some association with the temperature of the source of radiation. Given two bodies of different temperatures, the one with a higher temperature has its peak at a shorter wavelength (though assuming the bodies are of the same size, the one with the higher temperature emits more energy at every wavelength). Extremely low temperatures produce a peak in the "radio" band, and extremely high temperatures in the "gamma ray" band. Below are the temperature ranges that place the peak (based upon the log of the wavelength) within each EMR band:

temperature range where the spectrum peak falls
below 0.00367 K radio
0.00367-3.67 K microwave
3.67-4893 K infrared
4893-9174 K visible light
9174-367000 K ultraviolet
367000-4×108 K X-rays
above 4×108 K gamma rays

Black-body radiation from astronomical sources is typically infrared, visible light, or ultraviolet.

Further reading:

Referenced by pages:
atmospheric temperature profile
black body (BB)
brightness temperature (TB)
ionized carbon fine structure line ([CII])
circumstellar disk
cosmic microwave background (CMB)
CMB anisotropies
cold gas
color temperature (TC)
Compton scattering
continuous spectrum
continuum emission
dark matter
eclipse mapping
Europa Clipper
foreground subtraction
gray body
Hawking radiation
infrared (IR)
infrared excess (IRX)
Infrared Telescope Maffei (ITM)
line blanketing
Mars Observer (MO)
Mars Global Surveyor (MGS)
obscured fraction-luminosity relation
OH/IR source
1.3-mm observation
Planck function
power law
pulsar (PSR)
Rayleigh-Jeans law
radiative forcing (RF)
Rosseland mean opacity
secondary eclipse
spectral energy distribution (SED)
star formation rate (SFR)
shock wave
submillimeter galaxy (SMG)
spectral index (α)
standard model of a flare
stellar parameter determination
stellar temperature determination
synchrotron radiation
Sunyaev-Zel'dovich effect (SZ effect)
thermal bremsstrahlung
thermal emission
thermodynamic equilibrium (TE)
transition region
ultraluminous infrared galaxy (ULIRG)
Very Small Array (VSA)
Wien approximation
Wien's displacement law
X-ray burster (XRB)
X-ray source
Yarkovsky effect
Yarkovsky-O'Keefe-Radzievskii-Paddack effect (YORP)