47 Tucanae

47 Tucanae, also known as NGC 104, is a massive, bright globular cluster in the southern constellation Tucana. It is one of the brightest globular clusters visible from Earth.

Globular cluster: A dense, roughly spherical collection of old stars bound together by gravity. 47 Tucanae is a prominent example of this class of stellar system.
Gravitational relaxation: The gradual redistribution of stellar energies and orbits through repeated gravitational encounters. Repeated encounters help reshape 47 Tucanae’s dense stellar core.
47 Tucanae planetary transit survey: A Hubble Space Telescope search for transiting planets among stars in 47 Tucanae. Its null result challenged expectations for close-in giant planets in dense clusters.
Color–magnitude diagram: A plot comparing stars’ brightness with their color or temperature. Its sequence of stars reveals 47 Tucanae’s age and evolutionary stages.
Omega Centauri: The most massive known globular cluster associated with the Milky Way, located in Centaurus. It offers a mass and complexity comparison with 47 Tucanae.
Tucana: A southern constellation introduced by Dutch navigators in the late sixteenth century. The constellation gives 47 Tucanae its name and position on the sky.
Mass segregation: The tendency for more massive stars in a star cluster to concentrate toward its center. It helps explain the concentration of massive and evolved stars in the cluster’s core.
47 Tucanae X9: An ultracompact X-ray binary candidate in the globular cluster 47 Tucanae. X9 provides a detailed case study of compact binary evolution in the cluster.
Main-sequence fitting: A method for estimating a star cluster’s distance by matching its main sequence to calibrated stars. The cluster’s well-populated main sequence makes it useful for distance estimates.
M15: A dense globular cluster in Pegasus, also catalogued as NGC 7078. Its unusually dense core contrasts with the less extreme core of 47 Tucanae.

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Star clusterBroader topic: It is a well-studied example of a dense, old globular cluster.