48 2. LOOKING OUTWARD
Figure 2.17: e Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) as
photographed from near Casablanca, Chile. ey can be seen as the two fuzzy blobs near the
center top of the image. e Milky Way stretches downward from the upper left. Photograph
by the author.
2.5.3 GIANT ELLIPTICALS
e largest galaxies are the giant elliptical galaxies. Both giant and elliptical at the same time,
these behemoths may contain over 1 trillion stars. As is the case with most ellipticals, they are
mostly stars, with very little gas or dust. A good example is the galaxy M 87 in the Virgo Cluster
of Galaxies. At a distance of 16.4 Mpc, it is nearly 300 kpc across, six times the diameter of
the Milky Way. M 87 is at the center of a large cluster of galaxies called the Virgo Cluster (see
Section 2.6). It is not uncommon for a giant elliptical to lurk at the center of a large cluster of
galaxies.
2.6 CLUSTERS OF GALAXIES
Like stars, galaxies are often distributed in space in clusters, rather than simply randomly scat-
tered. Galaxy clusters are often given names corresponding to the constellation they appear to
2.6. CLUSTERS OF GALAXIES 49
Figure 2.18: e giant elliptical galaxy M 87. (Image credit: Nasa/STScI/Wikisky, Public Do-
main.)
lie within. Of course the constellations are simply chance groupings of stars comparatively quite
near to us; the galaxies are many orders of magnitude more distant.
2.6.1 THE LOCAL GROUP
Our own Milky Way galaxy is in a small cluster called the Local Group. It consists of two large
spiral galaxies—the Milky Way and the Andromeda Galaxy—along with another medium-sized
spiral galaxy (M 33) and many dozens of dwarf irregulars and dwarf ellipticals. e Local Group
is roughly 3 Mpc across.
2.6.2 THE VIRGO CLUSTER
e nearest large cluster of galaxies is the Virgo Cluster. It contains some 1500 galaxies, probably
many more if we could detect all of the faint dwarf galaxies presumably contained within. e
largest is the giant elliptical M 87, which lies near the cluster’s center. e center of the Virgo
cluster is about 16 Mpc distant, and it extends to a diameter of roughly 4.5 Mpc.
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