NGC104 - 47 TUCANAE

47 Tucanae is the second-largest and second-brightest globular cluster in the sky after Omega Centauri, located in the constellation Tucana at a distance of approximately 13,000 light-years from Earth. Appearing in the sky near the Small Magellanic Cloud (though vastly closer to us), it presents a dense, brilliant ball of stars spanning about 120 light-years in diameter. The cluster contains roughly one million stars and has a total mass estimated at about 700,000 solar masses. 47 Tucanae is classified as a core-collapsed or near-core-collapsed globular cluster, meaning its central region is extraordinarily dense, with stars packed so closely together that they are separated by only a fraction of a light-year. The dense core has been extensively studied by the Hubble Space Telescope, which has resolved individual stars down to the very center and revealed a rich population of exotic stellar objects. The cluster contains at least 23 millisecond pulsars, rapidly spinning neutron stars that have been spun up by accreting matter from companion stars in close binary systems. These pulsars are particularly common in dense globular clusters where stellar encounters frequently create and modify binary star systems. 47 Tucanae also hosts numerous blue straggler stars, which appear younger and hotter than they should given the cluster's age of roughly 13 billion years. These blue stragglers are thought to form through stellar mergers or mass transfer in binary systems, processes that are enhanced by the frequent stellar encounters in the cluster's dense environment. The cluster also made headlines when the Hubble Space Telescope conducted a deep search for transiting exoplanets within it, finding none, which suggested that the cluster's low metallicity may inhibit planet formation. For southern observers, 47 Tucanae is a breathtaking naked-eye object and one of the finest deep sky targets in any telescope.

The cluster spans about 120 light-years in diameter with approximately one million stars totaling about 700,000 solar masses, at a distance of 13,000 light-years and an age of roughly 13 billion years.