This image captures the stunning NGC 6535, a globular cluster 22,000
light-years away in the constellation of Serpens (The Serpent) that measures one
light-year across.
Globular clusters are tightly bound groups of stars which orbit galaxies. The
large mass in the rich stellar centre of the globular cluster pulls the stars
inward to form a ball of stars. The word globulus, from which these
clusters take their name, is Latin for small sphere.
Globular clusters are generally very ancient objects formed around the same
time as their host galaxy. To date, no new star formation has been observed
within a globular cluster, which explains the abundance of aging yellow stars in
this image, most of them containing very few heavy elements.
NGC 6535 was first discovered in 1852 by English astronomer John Russell
Hind. The cluster would have appeared to Hind as a small, faint smudge through
his telescope. Now, over 160 years later, instruments like the Advanced
Camera for Surveys (ACS) and Wide Field
Camera 3 (WFC3) on the NASA/ European Space Agency (ESA) Hubble Space
Telescope allow us to marvel at the cluster and its contents in greater detail.
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