Extragalactic astronomy is the branch of
astronomy concerned with objects outside the
Milky Way galaxy. In other words, it is the study of all astronomical objects which are not covered by
galactic astronomy.
The closest objects in extragalactic astronomy include the
galaxies
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...
of the
Local Group, which are close enough to allow very detailed analyses of their contents (e.g.
supernova remnants,
stellar associations). As instrumentation has improved, distant objects can now be examined in more detail and so extragalactic astronomy includes objects at nearly the edge of the observable universe. Research into distant galaxies (outside of our local group) is valuable for studying aspects of the universe such as galaxy evolution and
Active Galactic Nuclei (AGN) which give insight into physical phenomena (e.g.
super massive black hole
A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical o ...
accretion and the presence of dark matter). It is through extragalactic astronomy that astronomers and physicists are able to study the effects of
General Relativity such as
gravitational lensing
A gravitational lens is a distribution of matter (such as a galaxy cluster, cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This ...
and
gravitational waves, that are otherwise impossible (or nearly impossible) to study on a galactic scale.
Famous examples
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Hubble Deep Field
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LIGO's detection of
gravitational waves
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Chandra Deep Field South
The Chandra Deep Field South (CDF-S) is an image taken by the Chandra X-ray Observatory satellite. The location was chosen because, like the Lockman Hole, it is a relatively clear "window" through the ubiquitous clouds of H I region, neutral hydr ...
Topics
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Active Galactic Nuclei (AGN),
Quasar
A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a m ...
s
*
Dark Matter
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Galaxy clusters,
Supercluster
A supercluster is a large group of smaller galaxy clusters or galaxy groups; they are among the largest known structures in the universe. The Milky Way is part of the Local Group galaxy group (which contains more than 54 galaxies), which in turn ...
s
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Intergalactic stars
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Intergalactic dust
* the
observable universe
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Radio galaxies
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Supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
e
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Extragalactic planet
See also
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Andromeda–Milky Way collision
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Galaxy color–magnitude diagram
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Galaxy formation and evolution
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Observational cosmology
References
{{DEFAULTSORT:Extragalactic Astronomy
Astronomical sub-disciplines
Physical cosmology
Edwin Hubble