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Glossary term: Dark Matter

Description: Dark matter, translated from the German "dunkle (kalte) materie", refers to the non-luminous matter (potentially a particle) making up approximately a quarter of the Universe’s composition, and interacting extremely weakly with normal matter and the electromagnetic force, making direct detection challenging. Dark matter has been indirectly detected and inferred by measurements of the motion (velocities) of individual galaxies in clusters of galaxies, the motion (velocities) of stars and gas in galaxies, and gravitational lensing by clusters of galaxies. Currently, underground detectors around the world are trying to detect dark matter interactions in our galaxy, the Milky Way. The nature of dark matter is a topic of intense research and debate both in cosmology and particle physics.

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Term and definition status: This term and its definition is still awaiting approval

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

Measurements of how gravity distorts light in the galaxy cluster ZwCl0024+1652, shows a "ring" of dark matter in blue

Dark matter

Caption: This image of the galaxy cluster ZwCl0024+1652 is created using mathematical modelling, together with observations from the Hubble Space Telescope (HST). The Hubble observations were taken in November 2004 by the Advanced Camera for Surveys (ACS). The exquisite resolution of the ACS, allowed very detailed measurements to be made of the gravitational lensing in the cluster. The blue nebulosity is a superimposed ""map"" of the dark matter distribution in the galaxy cluster and is not visible in the observations, but is a mathematical model created based on the gravitational lensing data. The ""dark matter ring"" the is present in the image is one of the strongest pieces of evidence to date for the existence of dark matter. Observational data provides evidence that Dark matter makes up about 1/4 of the Universe, and is believed to make up the underlying structure of the cosmos. In addition, a large percentage the mass in galaxies and galaxy clusters is dark matter, which is not visible via direct observations.
Credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University) credit link
License: CC-BY-4.0 Creative Comments Attribution 4.0 International (CC BY 4.0) icons
Galaxies map, each dot is a galaxy, forming a web-like structure, the outer circle marks a distance of 2 billion light years

SDSS Redshift Map

Caption: This image shows a map of the distribution of galaxies and is based on redshift data from the Sloan Digital Sky Survey (SDSS). Redshift measurements provides information on the distances, positions and motions of the galaxies. The Earth is located at the center of the image, and each dot represents a galaxy. The outer circle represents a ""distance"" of about 2 billion light years. The idea of distance in cosmology is complex because the usual measurement of distance is the separation between two points in space at the same time. However, because of the speed of light, the further a distance, the farther back in time we are observing. The numbers on the outer circle are Right Ascension coordinates mapped onto a flat circle, and provides information on the position of the galaxies on the sky. The colours used represent the ages of the stars in the galaxies, the redder, more strongly clustered points represent galaxies comprising of older stars. The dark wedges that do not contain any dots are regions that were not mapped by the SDSS due to dust from the Milky Way galaxy obscuring the view.
Credit: M. Blanton and Sloan Digital Sky Survey credit link
License: CC-BY-4.0 Creative Comments Attribution 4.0 International (CC BY 4.0) icons