• noun a compact object in space that emits huge amounts of energy, sometimes equal to the energy output of an entire galaxy.
  • Quasars are apparently starlike objects characterised by enormous redshifts. They have been among the most discussed objects in astronomy and cosmology since their high redshifts were identified in 1963. Several thousand are now known. Quasars are so distant that they must be the nearest objects we can see to the origin of the universe, because of the time taken for light they have emitted to reach the Earth. They are now generally thought to have been extreme examples of active galactic nuclei, the energetic centres of unusual galaxies like Seyfert and N galaxies. They are observable in optical and radio wavelengths and the alteration of their light on its journey to us is a powerful probe of intergalactic space. Despite their name, quasars (the term is derived from ‘quasi-stellar radio source’) also exhibit structure, including jets of matter to one side of the starlike source. There is a school of thought that insists that some quasars are far nearer to us than their redshifts might imply, in other words that the redshifts are not ‘cosmological’, caused by the general expansion of the universe. This theory relies on the fact that more quasars than might be expected are seen near other comparatively nearby galaxies with which they appear to interact. Quasars are employed as a probe of the deep (and therefore early) universe: light from them reveals spectral lines characteristic of gas clouds and galaxies between them and the Earth. If the theory that they are distant objects from the early universe is correct, quasars were characteristic of the early universe and none are now shining.
  • It is an abbreviation of quasi-stellar object, quasi-stellar radio source, or quasi-stellar source. A class of celestial objects which when viewed through a telescope appear as stars, but which emit the energy of hundreds or thousands of galaxies. They are considered to be the most luminous objects in the known universe. Quasars that are also sources of radio waves are quasi-stellar radio sources, or quasi-stellar sources.
  • synonym quasi-stellar object
  • synonym quasi-stellar radio source
  • synonym quasi-stellar source

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