Astrophysics (Index)About


(addition of photons to a beam of EMR)

The term emission is used in the study of radiative transfer and spectroscopy, meaning the addition of photons to a beam of electromagnetic radiation (e.g., light), such as from changes in atoms, and also from scattering. It is the inverse of absorption, the removal of photons to the beam. The concept is used widely in astrophysics, for explaining and modeling stars, for dealing with the effects of the Earth's atmosphere, for explaining and modeling gas clouds, etc. Each type of emission has an absorption analog (though scattering is both emission and absorption), thus the classification of emission processes also is a classification of absorption processes.

Spontaneous emission is the emission of a photon by an atom not from any immediate interaction, such as the emission of a photon when an atom a lower level of atomic excitation (when an electron moves to a lower orbit).

Stimulated emission is the emission of a photon by a similar atom, but specifically when a photon of the same wavelength approaches and passes by. In this case, the emitted photon has the same characteristics as the photon that stimulated the emission, including its direction. Such stimulated emission is also referred to as negative absorption: on a macro scale, absorption suggests EMR passing through some material is attenuated, but if stimulated emission is occurring, it is possible that more EMR at the wavelength exits than entered. Masers and lasers are based on this effect, by setting up a configuration so that the "doubling" of photons happens repeatedly.

Scattering emission includes photons entering the beam through Thomson scattering or Compton scattering.

The term emission is also used within astronomy in a more general sense, for EMR produced by some object, and also for other produced particles (e.g., neutrinos) or waves (gravitational waves).

(physics,EMR,radiative transfer,photons)
Further reading:

Referenced by pages:
absorption line
active galaxy
advection dominated accretion flow (ADAF)
active galactic nucleus (AGN)
alpha CO (αCO)
anomalous microwave emission (AME)
atmospheric model
atomic excitation
Auger effect
broad emission line region
Be star
circumstellar disk
cosmic microwave background (CMB)
CMB anisotropies
continuum emission
cooling flow
cooling function
cosmic dust
Cygnus A (3C 405)
damping profile
dark matter
diffuse emission
Dwingeloo Obscured Galaxy Survey (DOGS)
Doppler broadening
DQ Tau
Dickel-Wendker-Bieritz Catalog (DWB)
electron orbital
electron scattering
emission line galaxy (ELG)
emission coefficient (j)
emission line
emission nebula
star formation feedback
GALEX Arecibo SDSS Survey (GASS)
gamma rays (GR)
Galactic All-sky Survey (GASS)
gamma-ray burst (GRB)
greenhouse effect
Hanle effect
helium 1083 nm line
hyperluminous infrared galaxy (HLIRG)
intensity mapping
IRAS 13224-3809
Kelvin-Helmholtz mechanism
Kirchhoff's law of thermal radiation
line blanketing
line broadening
luminous infrared galaxy (LIRG)
luminosity (L)
Lyman-Werner photon
Massive Cluster Survey (MACS)
magnetic field
microchannel array
natural broadening
NEO Surveyor
neutron star (NS)
nitrogen (N)
non-thermal emission
obscured fraction-luminosity relation
OH/IR source
PAH emissions
pulsar (PSR)
quantum number
radiation zone
radiative transfer (RT)
radio supernova (RSN)
redshift (z)
retrograde accretion
radio galaxy (RG)
radiative transfer code (RT code)
equation of radiative transfer (RTE)
radiative transfer model (RTM)
secondary eclipse
spectral band
spectral index (α)
spectral line
spectral signature
spectral type
spin (ms)
spin-down luminosity
spinning dust emission
standard model of a flare
state of excitation
stellar flare
synchrotron radiation
thermal bremsstrahlung
thermal dust emission
thermal emission
21-cm line
time-ordered data (TOD)
transit spectroscopy
transmission spectroscopy
ultra-fast outflow (UFO)
ultraluminous infrared galaxy (ULIRG)
X-ray burster (XRB)