Radiation astronomy/Electromagnetics

This is a colour composite image of RCW120. Credit: ESO/APEX/DSS2/ SuperCosmos/ Deharveng(LAM)/ Zavagno(LAM).

Radiation astronomy is often performed using electromagnetics. Electromagnetics are most familiar as light, or electromagnetic radiation.

The image at right is a colour "composite image of RCW120. It reveals how an expanding bubble of ionised gas about ten light-years across is causing the surrounding material to collapse into dense clumps where new stars are then formed. The 870-micron submillimetre-wavelength data were taken with the LABOCA camera on the 12-m Atacama Pathfinder Experiment (APEX) telescope. Here, the submillimetre emission is shown as the blue clouds surrounding the reddish glow of the ionised gas (shown with data from the SuperCosmos H-alpha survey). The image also contains data from the Second Generation Digitized Sky Survey (I-band shown in blue, R-band shown in red)."[1]

Electromagnetic radiation astronomy is a broader concept physics subject heading used by the American Physical Society (APS).[2]

Gamma rays

This is an image of quasar 3C 279 in gamma rays. Credit: NASA EGRET Compton observatory team.

Def. very high frequency (and therefore very high energy) electromagnetic radiation emitted as a consequence of radioactivity is called a gamma ray.

Def. electromagnetic radiation consisting of gamma rays is called gamma radiation.

Gamma rays typically have frequencies above 10 exahertz (or >1019 Hz), and therefore have energies above 100 keV and wavelengths less than 10 picometers (less than the diameter of an atom). However, this is not a hard and fast definition, but rather only a rule-of-thumb description for natural processes. Gamma rays from radioactive decay are defined as gamma rays no matter what their energy, so that there is no lower limit to gamma energy derived from radioactive decay. Gamma decay commonly produces energies of a few hundred keV, and almost always less than 10 MeV. In astronomy, gamma rays are defined by their energy, and no production process need be specified. The energies of gamma rays from astronomical sources range over 10 TeV, at a level far too large to result from radioactive decay. A notable example is extremely powerful bursts of high-energy radiation normally referred to as long duration gamma-ray bursts, which produce gamma rays by a mechanism not compatible with radioactive decay.

"The unusually wide span of the gamma-ray spectral window [covers] at least ten decades of photon energies (~105 - 1015 eV)".[3]

The Rosemary Hill Observatory (RHO) started observing 3C 279 in 1971,[4] and was further observed by the Compton Gamma Ray Observatory in 1991, when it was unexpectedly discovered to be one of the brightest gamma ray objects in the sky.[5] It is also one of the most bright and variable sources in the gamma ray sky monitored by the Fermi Space Telescope. Apparent superluminal motion was detected during observations first made in 1973 in a jet of material departing from the quasar, though it should be understood that this effect is an optical illusion caused by naive estimations of the speed, and no truly superluminal motion is occurring.[6]

Markarian (Mrk) 1501 is the first Seyfert I galaxy to have superluminal motion.[7] Mrk 1501 is an ultraviolet, X-ray, and gamma-ray source.

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