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Dark Matter A term used to describe matter that can be inferred to exist from its gravitational effects, but does not emit or absorb detectable amounts of light. Observations of the rotational speed of spiral galaxies, the confinement of hot gas in galaxies and clusters of galaxies, the random motions of galaxies in clusters, the gravitational lensing of background objects, and the observed fluctuations in the cosmic microwave background radiation require the presence of additional gravity, which can be explained by the existence of dark matter. The evidence suggests that the mass of dark matter in galaxies, clusters of galaxies, and the universe as a whole is about five or six times greater than the mass of ordinary light-emitting matter that makes up stars, planets, gas and dust.
Albert Einstein, 1947. Einstein used his "cosmological constant" to help describe a static universe. When he learned the universe was expanding, he discarded it.
Gravity always pulls matter together.
So what is dark energy?
Dark Universe / Transient Universe | Outer Solar System | Near Earth Objects | Milky Way | LSST Tour Dark Matter | Dark Energy | 3D mass Illustration of strong gravitaional lensing.
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We believe that most of the matter in the universe is dark , i.e. cannot be detected from the light which it emits (or fails to emit).
In the 1978 follow-up album to "Born to Run," Bruce Springsteen uses darkness on the edge of town as a metaphor for the desolate unknown we all face as we grow up and try to understand the world. Cosmologists working to decipher the origin and fate of the universe must identify completely with The Boss' sense of tragic yearning.
There are many reasons to believe that the universe is full of " dark matter ", matter that influences the evolution of the universe gravitationally, but is not seen directly in our present observations. FIGURE: Superposed on an optical picture of a group of galaxies is an X-ray image taken by ROSAT .
When the Universe was young, it was nearly smooth and featureless. As it grew older and developed, it became organized.
Estimated distribution of matter and energy in the universe, today (top) and when the CMB was released (bottom)
Dark Energy, Dark Matter