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Galaxies
have been categorized according to their apparent shape usually referred to
as their visual morphology). A common form is the elliptical galaxy, which
has an ellipse-shaped light profile. Spiral galaxies are disk-shaped
assemblages with curving, dusty arms. Galaxies with irregular or unusual
shapes are known as peculiar galaxies, and typically result from disruption
by the gravitational pull of neighboring galaxies. Such interactions between
nearby galaxies, which may ultimately result in galaxies merging, may induce
episodes of significantly increased star formation, producing what is called
a starburst galaxy. Small galaxies that lack a coherent structure could also
be referred to as irregular galaxies |
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Elliptical
galaxies were denoted by the letter E and a number
describing
the galaxy's apparent shape - 0 for a completely round form, 5 for
one twice as long as wide, and 7 for the apparently flattest genuine
ellipticals. We do not know, solely from an image, the true shape of
such a galaxy; the same galaxy might have quite different degrees of
flattening if viewed from different directions. Elliptical galaxies
are, in general, characterized by old stellar populations and very little
of the gas and dust needed to form new stars. |
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Sky and telescopes |
Galaxies
are the lighthouses that plumb the Universe - constituents of
the largest-scale texture we know. They span a vast range of properties,
from dwarf galaxies with a few million stars barely outshining the
brightest individual star clusters in our own galaxy, to vast assemblages
of a trillion stars in the centers of great clusters. Our own galaxy,
a reasonably bright spiral system, can be traced at least fifty thousand
light-years from its nucleus, and we know of many
galaxies much larger.
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