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Dark Matter - Introduction

Dark Matter - Introduction

Dark matter Dark matter is invisible. Based on the effect of gravitational lensing, a ring of dark matter has been detected in this image of a galaxy cluster (CL0024+17) and has been represented in blue.[1] Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but accounts for most of the matter in the universe. Astrophysicists hypothesized dark matter because of discrepancies between the mass of large astronomical objects determined from their gravitational effects and the mass calculated from the observable matter (stars, gas, and dust) that they can be seen to contain. Although the existence of dark matter is generally accepted by the mainstream scientific community, some alternative theories of gravity have been proposed, such as MOND and TeVeS, which try to account for the anomalous observations without requiring additional matter. Overview[edit] Estimated distribution of matter and energy in the universe, today (top) and when the CMB was released (bottom)

Martin White: Dark Matter 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). This is "stuff" which cannot be seen directly -- so what makes us think that it exists at all? Its presence is inferred indirectly from the motions of astronomical objects, specifically stellar, galactic, and galaxy cluster/supercluster observations. For each of the stellar, galactic, and galaxy cluster/supercluster observations the basic principle is that if we measure velocities in some region, then there has to be enough mass there for gravity to stop all the objects flying apart. Dark matter has important consequences for the evolution of the Universe and the structure within it. Note that the dynamics of the Universe are not determined entirely by the geometry (open, closed or flat) unless the Universe contains only matter. Dark matter (DM) candidates are usually split into two broad categories, with the second category being further sub-divided:

How Dark Matter Works" 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. These stargazing scientists have been facing their own darkness on the edge of town (or on the edge of galaxies) for a long time as they try to explain one of astronomy's greatest mysteries. It's known as dark matter, which is itself a placeholder – like the x or y used in algebra class – for something unknown and heretofore unseen. One day, it will enjoy a new name, but today we're stuck with the temporary label and its connotations of shadowy uncertainty. Just because scientists don't know what to call dark matter doesn't mean they don't know anything about it. So what is dark matter?

Dark Matter 2 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. Click for full-size image. Strong gravitational lensing happens when there is so much mass contrast in the lens that the light rays from a distant source bend around both sides of the lens and cross near Earth. Then multiple images of the source may be seen. Clicking on each image below will bring up MPEG movies (800 kB) showing the evolution of the distortion as the clusters move against the background over half billion years. Two simulations of strong lensing by a massive cluster of galaxies.

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