Quasar:
“A quasar (/ˈkweɪzɑːr/) (also quasi-stellar object
or QSO) is an active galactic nucleus of very high luminosity.”
“A quasar consists of a super massive black hole
surrounded by an orbiting accretion disk of gas.”
As gas in the
accretion disk falls toward the black hole, energy is released in the form of
electromagnetic radiation.
Quasars emit energy across the electromagnetic
spectrum and can be observed at radio, infrared, visible, ultraviolet, and
X-ray wavele
The term "quasar" originated as a
contraction of "quasi-stellar radio source", because quasars were
first identified as sources of radio-wave emission, and in photographic images
at visible wavelengths.
They
resembled point-like stars. High-resolution images of quasars, particularly
from the Hubble Space Telescope, have demonstrated that quasars occur in the centres
of galaxies, and that some quasar host galaxies are strongly interacting or
merging galaxies.
Quasars are found over a very broad range of
distances (corresponding to redshifts of roughly 0.1 to 7), and quasar
discovery surveys have demonstrated that quasar activity was more common in the
distant past.
The peak epoch of quasar activity in the Universe
corresponds to red shifts around 2, or approximately 10 billion years ago.
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