Knowra Astrophysical maser Astrophysical maser An astrophysical maser is an astronomical source of intense, narrow-band microwave or radio emission produced when excited gas amplifies radiation through stimulated emission.
Stimulated emission : An excited atom or molecule emits a photon when triggered by an incoming photon, producing a matching second photon. This emission process lets photons multiply coherently as they pass through astronomical gas.
Water maser : Microwave emission from the 22-gigahertz rotational transition of water vapor molecules. Water masers trace compact, warm gas around young stars and active galactic nuclei.
Orion KL : A chemically rich, active region within the Orion Molecular Cloud complex. Its many maser species make it a benchmark for studying massive star formation.
Molecular cloud : A cold, dense interstellar cloud composed primarily of molecular hydrogen and dust. Many astrophysical masers form in dense molecular material near young stars.
Thermal emission : Radiation emitted by matter because of its temperature, with a spectrum shaped by thermal particle motions. Unlike thermal emission, maser radiation can be exceptionally bright and concentrated in narrow lines.
Population inversion : A state in which more particles occupy an excited energy level than a lower one. The inversion makes stimulated emission exceed absorption in the masing gas.
Hydroxyl maser : Radio emission amplified by stimulated emission from hydroxyl molecules, especially near 1.6 gigahertz. Hydroxyl masers mark environments including star-forming regions and evolved stars.
W3(OH) : A massive star-forming region in the constellation Cassiopeia, known for strong hydroxyl and methanol masers. Its maser emission helped establish how radio lines trace sites of massive star birth.
Star formation : The process by which dense regions of interstellar gas collapse to form stars. Young stars heat and irradiate nearby gas, creating common maser conditions.
Synchrotron radiation : Radiation emitted by relativistic charged particles spiraling in magnetic fields. It produces broad radio continua, rather than molecular spectral lines amplified by stimulated emission.
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