Hubble Deep View of a Spiral Galaxy
NGC 4921 in the Coma Cluster Illustrates the Parts of a Galaxy
Feb 16, 2009
The Hubble Space Telescope has taken an image of NGC 2941 (also known as Abell 1656), part of the Coma Galaxy Cluster. A total of 27 hours' exposure time were used to create this picture.
Galactic Regions Visible in the NGC 4921 Image
NGC 4921 is a round spiral galaxy seen face-on. The spiral structure is visible with star-forming regions seen as bright bluish veins and speckles. The dark swirls are dusty lanes in the the galaxy. Although there are billions of stars in the galaxy, they are spread out enough that background galaxies can be seen, even behind the dusty patches. The nucleus and central core of the galaxy where the stars are packed the thickest does not allow for views to the background. Many spiral galaxies have a central bar structure, and one can be seen here oriented horizontally.
Globular clusters are spheroid collections of stars densely packed together that orbit the galaxy outside of its main bulk. Some of NGC 4921's globular clusters are indicated in the labeled image. Dwarf galaxies are also visible in the image as the hazy patches just above the galaxy that have their own centers of gravity. Dwarf companion galaxies also orbit the Milky Way, such as the Large and Small Magellanic Clouds.
The Location of NGC 4921
Except for the two stars near the top, everything in the photo is far beyond the Milky Way Galaxy. NGC 4921 lies 320 million light-years from Earth. There are approximately 1000 galaxies in the Coma Galaxy Cluster. NGC 4921 is a magnitude 12 galaxy, therefore it would require a large telescope for amateurs to spot it. NGC 4921 is in the constellation Coma Berenices, which represents the hair of Queen Berenice. Coma Berenices is found in the Northern Hemisphere, located between Canes Venatici and Virgo, best viewed in the spring.
Different Types of Galaxies
Galaxies in dense clusters often have different characteristics than galaxies that reside in more open space. The Coma Galaxy Cluster has mostly elliptical galaxies, which makes NGC 4921 somewhat unusual. Spiral galaxies are often distorted and merged in close spaces, creating the common elliptical shape. Another reason NGC 4921 is unusual is that it does not display vigorous star formation as other spirals do. Although there is some evidence of star formation in the spiral arms, the activity and spiral shapes are not as distinct as classical spirals. A few other spiral galaxies in the Coma Cluster are also visible in the image.
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