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Bulging galaxy baffles
Posted: November 18, 2009

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A recent Hubble image capturing edge-on galaxy NGC 4710 reveals a curious box-shape bulge with a faint, ethereal X-shaped structure pouring from its middle.

A faint X-shape structure is seen emanating from the boxy bulge of spiral galaxy NGC 4710. Image: NASA & ESA.

The Hubble image is part of a survey being conducted by astronomers to learn more about the evolution of galactic bulges, an ample component to most spiral galaxies. Edge-on galaxies are prime targets, since this configuration allows their bulges to be easily distinguished from the surrounding disc of material.

This extraordinarily detailed image of NGC 4710 was captured by Hubble's Advanced Camera for Surveys (ACS) and clearly reveals the galaxy's bulge and its disc, a luminous elongated white plane running through the galaxy. Both disc and bulge are pockmarked with ghostly dust lanes.

A delicate X-shaped structure can be seen emanating from the galaxy's core. Astronomers call this feature a boxy or peanut-shaped bulge, and appears due to the vertical motion of stars in the galaxy's bar. This phenomenon is only visible in edge-on galaxies and is a common occurrence in spiral galaxies with small bulges and open arms. NGC 4710, however, has spiral arms wrapped tightly around its prominent bulge.

The tuning fork diagram provides a simple way of classifying galaxies. Image: NASA.

In the standard 'tuning fork' diagram derived by Edwin Hubble to classify galaxies according to structure, NGC 4710 is an S0 or lenticular type galaxy, displaying traits common to both spiral and elliptical galaxies. Astronomers are keen to study this population of galaxy to determine how many globular clusters they host, since globular clusters may represent the processes that build bulges.

There are two contending processes for the formation of the bulges characteristic to spiral galaxies: either they formed rapidly in the early Universe, before the spiral disc and arms formed, or they built up from material accumulating from the disc during a prolonged evolution. Researchers have not seen very many globular clusters associated with NGC 4710's bulge, suggesting that its assembly mainly involved relatively slow processes.

NGC 4710 is a member of the Virgo Cluster of galaxies and lies 60 million light years from Earth in the northern constellation of Coma Berenices.

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