take the form of ellipsoids, with no spiral structure or flattened disks.
Elliptical galaxies constitute approximately 10% of observed galaxies.
Examples of Elliptical Galaxies
The adjacent image shows an example, the
giant elliptical galaxy
M87 in the center
(click on the image for a larger version).
Some other examples of elliptical galaxies include
M32, which is an
E2 dwarf elliptical near the Andromeda Galaxy,
and the E6 elliptical galaxy
M110, another satellite of the Andromeda Galaxy.
The Hubble Classification
In the Hubble
sequence E0, E1, E2, ... E7, the number is related to how flattened the ellipse
appears to be, with E0 corresponding to no flattening and E7 to a very elongated
ellipse. The Hubble classification
scheme uses the apparent
ellipticity, so it refers to the projection of the
galaxy's shape on the celestial sphere, not its actual shape.
Properties of Elliptical Galaxies
The masses of elliptical galaxies cover a large range:
107 up to 1013 solar masses. The corresponding range of
diameters is about 1/10 kpc up to about 100 kpc, and
the absolute blue
magnitude varies over a correspondingly large range
from -8 to -23.
Thus, the smallest of the elliptical galaxies, which are called dwarf
ellipticals, may be only a little larger than globular clusters, while the
giant elliptical galaxies like M87
are among the largest galaxies in the Universe. This is a much larger
range in size than is seen for the spiral galaxies.
Elliptical galaxies exhibit far less evidence for young stars,
gas, or dust than do spiral galaxies, and have larger random motion of stars than
in spiral galaxies where the motion is a more ordered rotation.