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Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but accounts for most of the matter in the universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, on radiation, and on the large-scale structure of the universe. Dark matter has not been detected directly, making it one of the greatest mysteries in modern astrophysics. Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level. According to the Planck mission team, and based on the standard model of cosmology, the total mass–energy of the known universe contains 4.9% ordinary (baryonic) matter, 26.8% dark matter and 68.3% dark energy. Thus, dark matter is estimated to constitute 84.5% of the total matter in the universe, while dark energy plus dark matter constitute 95.1% of the total mass–energy content of the universe.
The following photo is in the public domain because it was created by NASA and ESA.
Astronomers using NASA's Hubble Space Telescope have discovered a ghostly ring of dark matter
that formed long ago during a titanic collision between two massive
galaxy clusters. The ring's discovery is among the strongest evidence
yet that dark matter exists. Astronomers have long suspected the
existence of the invisible substance as the source of additional gravity
that holds together galaxy clusters. Such clusters would fly apart if
they relied only on the gravity from their visible stars. Although
astronomers don't know what dark matter is made of, they hypothesize
that it is a type of elementary particle that pervades the universe.
This Hubble composite image shows the ring of dark matter in the galaxy
cluster CL 0024+17.
The ring-like structure is evident in the blue map of the cluster's
dark matter distribution. The map was derived from Hubble observations
of how the gravity of the cluster Cl 0024+17 distorts the light of more
distant galaxies, an optical illusion called gravitational lensing.
Although astronomers cannot see dark matter, they can infer its
existence by mapping the distorted shapes of the background galaxies.
The map is superimposed on a Hubble Advanced Camera for Surveys image of
the cluster taken in November 2004.
NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)
Dark matter is invisible. Based on the effect of gravitational lensing, a ring of dark matter has been inferred in this image of a galaxy cluster (CL0024+17) and has been represented in blue.
A massive cluster of yellowish galaxies, seemingly caught in a red and blue spider web of eerily distorted background galaxies, makes for a spellbinding picture from the new Advanced Camera for Surveys aboard NASA's Hubble Space Telescope. To make this unprecedented image of the cosmos, Hubble peered straight through the center of one of the most massive galaxy clusters known, called Abell 1689. The gravity of the cluster's trillion stars — plus dark matter — acts as a 2-million-light-year-wide lens in space. This gravitational lens bends and magnifies the light of the galaxies located far behind it. Some of the faintest objects in the picture are probably over 13 billion light-years away (redshift value 6).
This file is in the public domain because it was created by NASA and ESA.