I was always amazed at the vast amount of objects that lie in the sky –
planets, stars, star clusters, galaxies, clusters of galaxies. I am even
more amazed because of the large variety of sizes and distances.
Take for example the dwarf galaxy DDO 82, also known as UGC 5692. In the first
image of this page, taken from the DSS2 survey, the field of view is 15
arcminutes, about half of the angular diameter of the full moon. UGC 5692 is in
the red circle in the lower left and appears visually similar in size and color
to another galaxy, UGC 5612, visible within the circle on the right. However,
this second galaxy, a barred spiral, is certainly larger, since it lies at a
much greater distance: UGC 5692 is in fact "only" 13 million light years from
us, while UGC 5612 is over 62 million light years away.
In the second
image, centered on UGC 5692, the field of view is reduced and the dwarf galaxy
appears somewhat larger. The third image is a total view of the galaxy, obtained
with the Hubble Space Telescope.
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The dwarf galaxy UGC 5692 (or DDO 82) is visible in the circle on the
left, whilst the more distant barred spiral UGC 5612 is in the circle on
the right. The field of view is 15 arcminutes. Credit: DSS2 /
SkyMap.org
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Zoom on UGC 5692. Credit: DSS2 / SkyMap.org
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A vapour of stars. A Hubble Space Telescope image of UGC
5692. Credit: ESA/Hubble & NASA
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Here is the image caption from the ESA Hubble Space Telescope website:
Relatively few galaxies possess the sweeping, luminous spiral arms or brightly
glowing centre of our home galaxy the Milky Way. In fact, most of the
Universe's galaxies look like small, amorphous clouds of vapour. One of these
galaxies is DDO 82, captured here in an image from the NASA/ESA Hubble Space
Telescope. Though tiny compared to the Milky Way, such dwarf galaxies still
contain between a few million and a few billion stars.
DDO 82, also
known by the designation UGC 5692, is not without a hint of structure,
however. Astronomers classify it as an Sm galaxy, or Magellanic spiral galaxy,
named after the Large Magellanic Cloud, a dwarf galaxy that orbits the Milky
Way. That galaxy, like DDO 82, is said to have one spiral arm.
In
the case of DDO 82, gravitational interactions over its history seem to have
discombobulated it so that this structure is not as evident as in the Large
Magellanic Cloud. Accordingly, astronomers also refer to DDO 82 and others of
a similar unshapely nature as dwarf irregular galaxies.
DDO 82 can
be found in the constellation of Ursa Major (the Great Bear) approximately 13
million light-years away. The object is considered part of the M81 Group of
around three dozen galaxies. DDO 82 gets its name from its entry number in the
David Dunlap Observatory Catalogue. Canadian astronomer Sidney van den Bergh
originally compiled this list of dwarf galaxies in 1959.
The image
is made up of exposures taken in visible and infrared light by Hubble’s
Advanced Camera for Surveys. The field of view is approximately 3.3 by 3.3
arcminutes.
All the following images are details from the 47.4 MB full resolution image
available at the ESA Hubble website. It may be noted, along with the "fog" of
stars that forms the body of UGC 5692, a few foreground stars and a myriad of
background galaxies, the most visible where the "fog" thins. All of these
background galaxies are completely invisible in the wide-field DSS2 image. Only
the keen eye of Hubble is able to discover them and it gives us an idea of how
much wealth of foreign, immense, distant galaxies lies in a fraction of the sky
large just over a tenth of the full moon's angular diameter.
