A globular cluster
is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is derived from the Latin globulus
—a small sphere. A globular cluster is sometimes known more simply as a globular
The term " globular cluster" has been applied to those clusters of stars which evidently occupy a space of more or less spherical form. Some of these "balls of stars," as they have been called, are truly wonderful, and are among the most interesting objects visible in the stellar heavens. Good specimens of the globular class are, however, are not very common objects, and there are not as many in the northern hemisphere as there are in the southern hemisphere.
[hide][top]Northern Hemisphere Globular Clusters
Prominent globular clusters in the northern hemisphere include M13
, and M5
Most beautiful southern hemisphere clusters are not visible in the northern hemisphere.
[hide][top]Southern Hemisphere Globular Clusters
Most of the beautiful northern hemisphere clusters can be seen in the southern hemisphere, such as Australia - and this includes M13 (the Hercules Cluster). The most wonderful globular clusters in the sky are 47 Tucanae, and Omega Centauri
[hide][top]Astronomy of Globular Clusters
Globular clusters, which are found in the halo of a galaxy, contain considerably more stars and are much older than the less dense galactic, or open clusters
, which are found in the disk. Globular clusters are fairly common; there are about 150 to 158 currently known globular clusters in the Milky Way
, with perhaps 10 to 20 more still undiscovered. Large galaxies can have more: Andromeda
, for instance, may have as many as 500. Some giant elliptical galaxies
, particularly those at the centers of galaxy clusters, such as M87
, have as many as 13,000 globular clusters. These globular clusters orbit the galaxy out to large radii, 40 kiloparsecs
(approximately 131,000 light-years
) or more.
Every galaxy of sufficient mass in the Local Group
has an associated group of globular clusters, and almost every large galaxy surveyed has been found to possess a system of globular clusters. The Sagittarius Dwarf
and Canis Major Dwarf
galaxies appear to be in the process of donating their associated globular clusters (such as Palomar 12
) to the Milky Way
. This demonstrates how many of this galaxy's globular clusters might have been acquired in the past.
Although it appears that globular clusters contain some of the first stars to be produced in the galaxy, their origins and their role in galactic evolution are still unclear. It does appear clear that globular clusters are significantly different from dwarf elliptical galaxies
and were formed as part of the star formation of the parent galaxy rather than as a separate galaxy. However, recent conjectures by astronomers suggest that globular clusters and dwarf spheroidals
may not be clearly separate and distinct types of objects.
Astronomers use the Shapley–Sawyer Concentration Class
to describe Globular Clusters
[hide][top]Globular Cluster Sketches
[hide][top]Globular Cluster Astrophotos
Below is a picture of M80, a gobular cluster... M80.jpg