Say, “M9,” to a soldier, and he’ll think of a Beretta pistol. Say, “M9,” to an astronomer and he’ll think of this star cluster. Charles Messier described the 9th entry in his astronomical catalog as “Nebula, without star, in the right leg of Ophiuchus …”. But Messier 9 (M9) does have stars; it’s known to modern astronomers as a globular cluster of over 300,000 stars within a diameter of only about 90 light-years. It lies some 25,000 light-years distant, near the central bulge of our Milky Way galaxy. This Hubble Space Telescope close-up resolves the dense swarm of stars across the cluster’s central 25 light-years. The stars are at least twice the age of the Sun and deficient in heavy elements. The stars’ colors correspond to their temperatures. Redder stars are cooler, bluer stars are hotter. Many of the cluster’s cool red giant stars show a yellowish tint in this sharp Hubble view.

Image Credit : NASA

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