Many galaxies 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 of the Virgo cluster (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: from about 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.

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