A new image of the bulge at the center of a distant spiral
galaxy, taken by the Hubble Space Telescope, is giving astronomers insight into
how these galactic paunches form.
The image of NGC 4710 is part of a survey that astronomers
have conducted to learn more about the formation of bulges, which are a
substantial component of most spiral
galaxies.
When targeting spiral galaxy bulges, astronomers often seek
edge-on galaxies, as their bulges are more easily distinguishable from the
disc. The detailed edge-on view of NGC 4710, taken with Hubble's Advanced
Camera for Surveys, shows the galaxy's bulge in its brightly colored center.
The luminous, elongated white plane that runs through the
bulge is the galaxy disc. The disc and bulge are surrounded by eerie-looking
dust lanes.
When staring directly at the center of the galaxy, one can
detect a faint, ethereal "X"-shaped structure. Such a feature, which
astronomers call a "boxy" or "peanut-shaped" bulge, is due to the vertical
motions of the stars in the galaxy's bar and is only evident when the galaxy is
seen edge-on.
This curiously shaped puff is often observed in spiral
galaxies with small bulges and open arms, but is less common in spirals with
arms tightly wrapped around a more prominent bulge, such as NGC 4710.
NGC 4710 is a member of the giant Virgo Cluster of galaxies
and lies in the northern constellation of Coma Berenices (the Hair of Queen
Berenice). William Herschel discovered the galaxy in the 1780s and noted it
simply as a "faint nebula."
It lies about 60 million light-years from the Earth and is
an example of a lenticular or S0-type galaxy — a type that seems to have some
characteristics of both spiral
and elliptical galaxies.
Astronomers are scrutinizing these systems to determine how
many globular clusters they host. Globular clusters are thought to represent an
indication of the processes that can build
bulges.
Two quite different processes are believed to be at play
regarding the formation of bulges in spiral galaxies: either they formed rather
rapidly in the early universe, before the spiral disc and arms formed; or they
built up from material accumulating from the disc during a slow and long
evolution.
In the case of NGC 4710, researchers have spotted very few
globular clusters associated with the bulge, indicating that its assembly
mainly involved relatively slow processes.
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