Messier 15

Messier 15 is a dense globular star cluster in Pegasus, about 33,600 light-years from Earth. Its unusually concentrated core and central millisecond pulsar make it a notable target for studying stellar dynamics.

Globular cluster: A roughly spherical, gravitationally bound collection of old stars orbiting a galaxy. Messier 15 is a compact example of this stellar system type.
Pulsar: A rotating neutron star that emits beams of electromagnetic radiation observed as periodic pulses. Messier 15's central millisecond pulsar belongs to this broader class of neutron stars.
Charles Messier: A French astronomer who compiled a catalog of nebulae and star clusters in the eighteenth century. He recorded Messier 15 in his catalog in 1746.
RR Lyrae variable: A pulsating horizontal-branch star with a regular period and a useful luminosity–period relation. RR Lyrae stars in Messier 15 help calibrate its distance.
Kuestner 1: A planetary nebula located within the globular cluster Messier 15. It is one of the rare planetary nebulae known inside a globular cluster.
Core collapse: The contraction of a star cluster's central region as gravitational encounters transfer energy outward. Messier 15's exceptionally concentrated center is commonly associated with this dynamical process.
Neutron star: An ultra-dense stellar remnant composed predominantly of neutrons, formed in some supernovae. The cluster's pulsar is a neutron star whose rapid rotation produces its observed pulses.
Messier catalog: A catalog of nebulae, clusters, and galaxies compiled by Charles Messier and collaborators. Messier 15 is entry 15 in this catalog of prominent nonstellar objects.
Color–magnitude diagram: A plot comparing stars' colors and brightnesses to reveal their evolutionary stages and populations. Messier 15's diagram separates its old stars into recognizable evolutionary sequences.
Pease 1: A planetary nebula projected against the globular cluster Messier 15 and associated with it. Its discovery made Messier 15 a landmark case for planetary nebulae in globular clusters.

Linked from 1 page