Radio sources are objects in outer space that emit strong radio waves. Radio emission comes from a wide variety of sources. Such objects represent some of the most extreme and energetic physical processes in the universe.
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History
In 1932, radio astronomer Karl Jansky detected radio waves coming from an unknown source in the centre of our galaxy. This was the first time that radio waves were detected from outer space.[1] The first radio sky survey was conducted by Grote Reber and was completed in 1941. In the seventies, some stars in our galaxy were found to be radio emitters, one of the strongest being the unique binary MWC 349. [2] [3]
The Sun
As the nearest star, the Sun is the brightest radiation source in most frequencies, including the radio spectrum below 1 m.
The Galactic Center
The center of the Milky Way was the first radio source to be detected. It contains a number of radio sources, including Sagittarius A and the supermassive black hole at Sagittarius A*.
Supernova remnants
Supernova remnants often show diffuse radio emission. Examples include Cassiopeia A, the brightest extrasolar radio source in the sky, and the Crab Nebula.
Pulsars
Supernovas sometimes leave behind dense spinning neutron stars called pulsars. They emit jets of charged particles which emit synchrotron radiation in the radio spectrum. Examples include the Crab Pulsar, the first pulsar to be discovered.
Star forming regions
Short radio waves are emitted from complex molecules in dense clouds of gas where stars are giving birth.
Spiral galaxies contain clouds of neutral hydrogen and carbon monoxide which emit radio waves. The radio frequencies of these two molecules were used to map a large portion of the Milky Way galaxy.[4]
Radio galaxies
Many galaxies are strong radio emitters. Some of the more notable are Centaurus A and Messier 87.
Quasars (short for "quasi-stellar radio source") were one of the first point-like radio sources to be discovered. Quasars' extreme red shift led us to conclude that they are distant active galactic nuclei. Active galactic nuclei have jets of charged particles which emit synchrotron radiation. One example is 3C 273, the optically brightest quasar in the sky.
Merging galaxy clusters often show diffuse radio emission. [5]
Cosmic microwave background
The cosmic microwave background is blackbody background radiation left over from the Big Bang (the rapid expansion, roughly 13.7 billion years ago, that was the beginning of our universe).
References
- ^ Koupelis, Theo; Karl F. Kuhn (2007). In Quest of the Universe (5th ed.). Jones & Bartlett Publishers. p. 149. ISBN 0763743879. http://books.google.com/books?id=WwKjznJ9Kq0C. Retrieved 2008-04-02.
- ^ Braes, L.L.E. (1974). "Radio Continuum Observations of Stellar Sources". IAU Symposium No.60, Maroochydore, Australia, September 3-7, 1973: 377-381. Bibcode: 1974IAUS...60..377B.
- ^ Strelnitski, V.; Malatesta, K. (2007). "2029+40 V1478 Cyg (MWC 349)". AAVSO Variable Star of the Season, July 2007. http://www.aavso.org/vstar/vsots/0707.shtml.
- ^ Gonzalez, Guillermo; ay Wesley Richards (2004). The Privileged Planet. Regnery Publishing. p. 382. ISBN 0895260654. http://books.google.com/books?id=KFdu4CyQ1k0C. Retrieved 2008-04-02.
- ^ http://www.arcetri.astro.it/~buttery/thesis/node69.html
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