Groups of Galaxies (2) ...
In the Northern Hemisphere,
two galaxies of the local group are visible to the naked eye. The
Andromeda Galaxy
(M31)
is a great Sb spiral much like our own at a distance of about
3 million light years (900 kpc). To the naked eye it
is a faint fuzzy patch that appears, with binoculars, as a lens
shaped object.
It has two dwarf elliptical satellite galaxies visible through a
small telescope. The adjacent image shows M31 and the small elliptical companions
M32 (left) and M110 (right).
The other galaxy of the local group that is
visible to the naked eye is the spiral
M33 in
Triangulum, at a distance comparable to that of Andromeda.
It too is a spiral galaxy, but it is smaller than Andromeda and
therefore is harder to see.
The Nearest Galaxy
For some time it was thought that the Large
Magellanic Cloud was the galaxy nearest to the Milky Way.
However, in 1994, a small dwarf elliptical galaxy called the
Sagittarius Dwarf was discovered
to be closer than the Magellanic Clouds. The adjacent figure shows this small galaxy as the
hazy patch in the center of the image.
This galaxy
escaped detection until recently because it is small, faint, spread out,
and obscured by
intervening stars of the Milky Way (the larger bright spots in the image). It lies at a distance of
about 24 kpc, which is less than half of the distance to the Large Magellanic Cloud. Because of its
proximity to the Milky Way, it is probably being torn apart by tidal forces.
|
Some Nearby Groups of Galaxies
|
| Group Name |
Members |
Distance (Mpc)
|
| M81 |
8 |
3.1
|
| Sculptor |
6 |
1.8
|
| Centaurus |
17 |
3.5
|
| M101 |
5 |
7.7
|
| M66 + M96 |
~ 10 |
9.4
|
| NGC 1023 |
6 |
9.5 |
|
Adapted from An Introduction to Modern Astrophysics,
B. W. Carrol and D. A. Ostlie
|
|
Other Nearby Groups
Some other nearby groups of galaxies are listed in the adjacent table.
All told, there
are about 20 small groups of galaxies nearer to us than the
Virgo Rich Cluster, which is a large cluster of galaxies
lying at a distance of about 15 Mpc
that we shall
discuss shortly. Most galaxies in the Universe probably occupy small
groups and clusters such as the Local Group.
