Changes

==Composition==

==Composition==

The stars themselves that make up globular clusters are all metal-poor population II stars, similar to those located in the central budge of the Milky Way.  There is also no detectable gas or dust in these clusters.

The stars themselves that make up globular clusters are all metal-poor population II stars, similar to those located in the central budge of the [[Milky Way]].  There is also no detectable gas or dust in these clusters.

Globular clusters are further divided into two major groupings known as ''Oosterhoff groups'', the difference between the level of [[metallicity]] found in the stars in the cluster.  Clusters of the type I group are found to have somewhat weak metal absorption line in their spectra, while Type II have very weak metal lines.  As such, Type I clusters are referred to as "metal-rich" and Type II as "metal-poor".  Both types are metal-poor in comparison to population I stars found in the [[galactic disk]].<ref>van Albada, T. S.; Baker, Norman (1973). "On the Two Oosterhoff Groups of Globular Clusters". Astrophysical Journal 185: 477–498. do:10.1086/152434.</ref>  In the Milky Way, the more metal-poor type II clusters are located in the outer part of the galactic halo, while the more metal-rich clusters are found near the galactic budge.<ref>http://adsabs.harvard.edu/abs/1976AJ.....81.1095H</ref> Both types of globular cluster populations have been found in several galaxies, being most common in large [[elliptical galaxy|elliptical galaxies]].  What causes the difference between the two types of clusters is not exactly known.  Some scenarios to explain this include galaxy mergers, the absorption of satellite galaxies, and staggered star formation within galaxies.<ref>http://adsabs.harvard.edu/abs/2002astro.ph..7607Y</ref>

Globular clusters are further divided into two major groupings known as ''Oosterhoff groups'', the difference between the level of [[metallicity]] found in the stars in the cluster.  Clusters of the type I group are found to have somewhat weak metal absorption line in their spectra, while Type II have very weak metal lines.  As such, Type I clusters are referred to as "metal-rich" and Type II as "metal-poor".  Both types are metal-poor in comparison to population I stars found in the [[galactic disk]].<ref>van Albada, T. S.; Baker, Norman (1973). "On the Two Oosterhoff Groups of Globular Clusters". Astrophysical Journal 185: 477–498. do:10.1086/152434.</ref>  In the Milky Way, the more metal-poor type II clusters are located in the outer part of the galactic halo, while the more metal-rich clusters are found near the galactic budge.<ref>http://adsabs.harvard.edu/abs/1976AJ.....81.1095H</ref> Both types of globular cluster populations have been found in several galaxies, being most common in large [[elliptical galaxy|elliptical galaxies]].  What causes the difference between the two types of clusters is not exactly known.  Some scenarios to explain this include galaxy mergers, the absorption of satellite galaxies, and staggered star formation within galaxies.<ref>http://adsabs.harvard.edu/abs/2002astro.ph..7607Y</ref>