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The Galaxies |
Galaxies are large systems of stars and interstellar matter,
typically containing several million to some trillion stars, of masses
between several million and several trillion times that of our Sun, of
an extension of a few thousands to several 100,000s light years, typically
separated by millions of light years distance. They come in a variety
of flavors: Spiral, lenticular, elliptical and irregular
We live in a giant spiral galaxy, the Milky Way Galaxy,
of 100,000 light years diameter and a mass of roughly a trillion solar
masses. The nearest galaxy to the Milky Way is Sagittarius Dwarf galaxy.
This small galaxy is so close, it is being swallowed up by the Milky Way.
It lies 80,000 light years from the Sun and 52,000 light years from the
center of the Milky Way. The next nearest galaxy is the Large Magellanic
Cloud, 170,000 light years away. The Andromeda Galaxy, also a spiral,
is about 2,3 million light years distant. |

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Spiral
Spiral galaxies usually consist of two major components:
A flat, large disk which often contains a lot of interstellar matter (visible
sometimes as reddish diffuse emission nebulae, or as dark dust clouds)
and young (open) star clusters and associations, which have emerged from
them (recognizable from the bluish light of their hottest, short-living,
most massive stars), often arranged in conspicuous and striking spiral
patterns and/or bar structures, and an ellipsoidally formed bulge component,
consisting of an old stellar population without interstellar matter, and
often associated with globular clusters. The luminosity and mass relation
of these components seem to vary in a wide range, giving rise to a classification
scheme.
Our sun is one of several 100 billion stars in a spiral galaxy, the Milky
Way.
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Lenticular
These are, in short, "spiral galaxies without spiral
structure", i.e. smooth disk galaxies, where stellar formation
has stopped long ago, because the interstellar matter was used up. Therefore,
they consist of old population stars only, or at least chiefly. From
their appearance and stellar contents, they can often hardly be distinguished
from elliptical observationally. |
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Elliptical
Elliptical galaxies are actually of ellipsoidal shape, and
it is now quite safe from observation that they are usually triaxial .
They have little or no global angular momentum, i.e. do not rotate as
a whole (of course, the stars still orbit the centers of these galaxies,
but the orbits are statistically oriented so that only little net orbital
angular momentum sums up). Normally, elliptical galaxies contain very
little or no interstellar matter, and consist of old population stars
only. They appear like luminous bulges of spirals, without a disk component. |
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Irregular
Often due to distortion by the gravitation of their intergalactic neighbors,
these galaxies do not fit well into the scheme of disks and ellipsoids,
but exhibit peculiar shapes. A subclass of distorted disks is however
frequently occurring. |
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(C)
Copyright 1996 - 2022 by Andjelko Glivar. All rights reserved. This material
may not be published in any
form without permission. |
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