Messier 22

Messier 22 is a bright globular star cluster in Sagittarius, about 10,600 light-years from Earth. Its dense, ancient stellar population makes it one of the Milky Way’s prominent globular clusters.

Globular cluster: A dense, roughly spherical system of old stars bound together by gravity. Messier 22 belongs to this class of compact stellar systems.
Messier 22 X-ray sources: A population of X-ray-emitting objects detected in the globular cluster Messier 22. These sources expose energetic binaries and compact stellar remnants in the cluster.
Charles Messier: An eighteenth-century French astronomer who compiled a catalog of nebulae and star clusters. He included the cluster as the twenty-second entry in his catalog.
Color–magnitude diagram: A plot of astronomical objects’ brightness against color, used to study stellar populations. It maps Messier 22’s stars into evolutionary sequences.
Sagittarius (constellation): A zodiac constellation whose stars and deep-sky objects lie along the Milky Way. Messier 22 appears in this constellation’s direction.
Messier 22 planetary nebula: A planetary nebula within Messier 22, formed by gas expelled from an evolved star. It is a rare example of this brief stellar phase inside a globular cluster.
Messier catalog: A catalog of nebulae, star clusters, and galaxies compiled by Charles Messier. Messier 22 takes its name and familiar designation from this list.
Stellar evolution: The changes in a star’s structure and properties as it ages and exhausts nuclear fuel. Cluster stars of similar age reveal different stages of stellar evolution.
Milky Way: The barred spiral galaxy containing the Sun and billions of other stars. Messier 22 is one of its globular clusters.
Messier 22 black holes: Stellar-mass black holes identified as members of the globular cluster Messier 22. Their detection challenged expectations that clusters quickly eject most black holes.

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