Star whose luminosity varies in a characteristic way, with a rapid rise in brightness followed by a slower decline. The period of a Cepheid variable star is related to its luminosity, so a determination of this period can be used to obtain an estimate of the star's distance.
Region of a galaxy beyond the visible halo where dark matter is believed to reside.
Term used to describe the mass in galaxies and clusters whose existence we infer from rotation curves and other techniques, but which has not been confirmed by observations at any electromagnetic wavelength.
dark matter particle
Particle undetectable at any electromagnetic wavelength, but can be inferred from its gravitational influence.
Thick distribution of warm gas and stars around the galactic center.
The center of the Milky Way, or any other, galaxy. The point about which the disk of a spiral galaxy rotates.