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NGC 6681

M70 is a rich globular cluster in the heart of the the Milky Way as it passes through Sagittarius. This is a region of the sky that looks towards the core of the Galaxy, and is busy with clusters and nebulae. M70 is one of three globular clusters within a few thousand light years of one another, probably all lying within the Galaxy's central bulge, some 29,000 light years from the Solar System. Its companion clusters are M69, which is marginally brighter than M70, and the far less distinct NGC 6652.

This cluster forms an approximate sphere of stars with a diameter of about seventy light years. It is immensely old, dating back to the beginnings of the Milky Way Galaxy. This great age (it is no less than 12 thousand million years old, and may be older) is reflected by its dense core: the cluster seems to have undergone the process known as 'core collapse'. This is a process by which the gradual movement of stars out of the core over millions of years results in the remaining stars grouping more tightly together in the central regions of the cluster.


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