Hubble Spies Galaxy's Big Bulge
This Hubble Space Telescope image of the spiral galaxy NGC 4710 shows a faint, ethereal "X"-shaped bulge at the galaxy's center.
Credit: NASA & ESA

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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