Dark matter
Dark matter
In the 1970s, an astronomer called Vera Rubin was measuring the velocities of stars in other galaxies and noticed something strange: the stars at the galaxies' edges moved faster than had been predicted. To reconcile her observations with the law of gravity, scientists proposed that there is matter we can't see and called it dark matter.
Physicists are racing to find subatomic particles that could be the missing dark matter, which is thought to make up about 26% of the energy density of the Universe.
Image: A computer-generated image of dark matter's potential distribution across millions of light years of space
Watch and listen to clips from past programmes TV clips [8] Radio Programmes [2]
The particle detectors used for the UK Dark Matter Collaboration experiment are housed in a mine deep under the North Yorkshire Moors. The BBC's David Shukman finds out what the scientists are hoping to learn.
Hubble Space Telescope images provide evidence of dark matter's existence. Light from distant galaxies is bent by a gravitational lens created by the dark matter's mass in nearby galaxies.
Professor Tim Sumner explains how he hunts for elusive dark matter particles in Boulby mine in Yorkshire.
Sir Patrick Moore and his guests explain what galaxies are and discuss some of their interesting features.
In the 1970s, Professors James Peebles and Jeremiah Ostriker's computer model simulations of galaxies suggested that there are large amounts of unaccounted for matter in the Universe. However, their ideas did not gain wider acceptance until Vera Rubin's measurements of the speeds of stars in galaxies also suggested that there is missing matter, which is now known as dark matter. ["The size and mass of galaxies and the mass of the universe" copyright Ostriker and Peebles-The Astrophysical Journal 193 / "Dark Matter and the origin of galaxies and globular star clusters" copyright Peebles - The Astrophysical Journal 277: 470-477]
About Dark matter
In astronomy and cosmology, dark matter is a currently-undetermined type of matter which accounts for a large part of the mass of the universe, but neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly seen with telescopes. Dark matter is estimated to constitute 83% of the matter in the universe and 23% of the mass-energy.
Dark matter came to the attention of astrophysicists in recent decades due to discrepancies between the mass of large astronomical objects determined from their gravitational effects, and mass calculated from the "luminous matter" they contain; such as stars, gas and dust. It was first postulated by Jan Oort in 1932 to account for the orbital velocities of stars in the Milky Way and Fritz Zwicky in 1933 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe, including the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. According to consensus among cosmologists, dark matter is believed to be composed primarily of a new, not yet characterized, type of subatomic particle. The search for this particle, by a variety of means, is one of the major efforts in particle physics today. Though the existence of dark matter is generally accepted by the mainstream scientific community, some alternative theories have been proposed to explain the anomalies that dark matter is intended to account for, without hypothesizing dark matter.
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