Giant diffuse galaxy
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A Giant Diffuse Galaxy is a supermassive, eliptical galaxy that is usually located in the centre of a cluster of galaxies. They are often contracted to cD galaxies, or BCGs (for brightest cluster galaxies). [1] Giant diffuse galaxies are, on average, approximately 10 times more luminous than "regular" galaxies, and many times larger than a normal elliptical galaxy - some having diameters of over 6 million light years (compared to our galaxy, the Milky Way, which is thought to be only around 100 thousand light years).[1] Giant Diffuse Galaxies are usually the largest galaxies in their respective clusters, and are mostly located around the centre of the cluster.
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[edit] Growth
A theory persists that cD galaxies grow larger by accreting or coming together with other galaxies,[1] and this 'cannibalising' of smaller galaxies has actually been observed. Because Giant Diffuse Galaxies exist at the centre of a cluster of galaxies, there are many galaxies to 'feed' on. This form of growth can make cDs a great size bigger, contributing to their overwhelming diameter and luminosity.[1] However, there is usually a perimeter around the cD in which no smaller galaxies exist, because they have already been accreted. There are always remains of 'eaten' galaxies, appearing as a diffuse halo of gas and dust, hence the Giant Diffuse Galaxy terminology.[1] This halo can be up to 3 million light years in diameter. [2]
[edit] Dynamic Friction
Dynamic Friction is the catalytic factor of the forming of the cD galaxy at the centre of the cluster. [3] This process begins when the moving of a large galaxy in a cluster attracts other small galaxies in a wake behind it. This trail of smaller galaxies effectively slows the large galaxies path, and, losing kinetic energy, the galaxy will simply drift into the centre of the cluster. Once there, the large galaxy's (and it's trailing galaxies) stars and matter will become one with other galaxies in the cluster who have shared the same fate. [3] A Giant Diffuse Galaxy will result from this formation. [3]
[edit] See Also
[edit] References
- ^ a b c d e Curious About Astronomy?. Retrieved on 28 March, 2007.
- ^ Cosmos: The SAO Encyclopedia: cD galaxies. Retrieved on 29 March, 2007.
- ^ a b c cD galaxies and cannibalism. Retrieved on 29 March, 2007.
