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Mysterious Dark Matter Revealed

Image which proves the existence of dark matterDark matter cannot be directly detected via optical means. As such, many aspects of it are a matter for pure conjecture. Now, astrophysicists have made a breakthrough in proving the existence of dark matter.

What exactly is dark matter? The explanation from Space.com is as follows.

The normal matter in the cosmos —atoms that make up stars, planets, air and life—accounts for only a small fraction of what must exist, based on the fact that without an additional source of gravity, galaxies would fly apart and galaxy clusters could not hold together as they do. Nobody knows where all that gravity comes from, so scientists say there must be some invisible stuff out there, which they call dark matter. Its presence is indirectly supported by many observations. Given what's known, this is the makeup of the universe:
  • 5 percent normal matter
  • 25 percent dark matter
  • 70 percent dark energy
Dark energy is an even more mysterious phenomenon, a force of some sort that beats out gravity and is causing the universe to expand at an ever-faster pace.

According to Chandra X-Ray observatory, the evidence for the existence of dark matter is as follows.

Hot gas detected by Chandra in X-rays is seen as two pink clumps in the image and contains most of the "normal," or baryonic, matter in the two clusters.The bullet-shaped clump on the right is the hot gas from one cluster, which passed through the hot gas from the other larger cluster during the collision. An optical image from Magellan and the Hubble Space Telescope shows the galaxies in orange and white. The blue areas in this image show where astronomers find most of the mass in the clusters. The concentration of mass is determined using the effect of so-called gravitational lensing, where light from the distant objects is distorted by intervening matter. Most of the matter in the clusters (blue) is clearly separate from the normal matter (pink), giving direct evidence that nearly all of the matter in the clusters is dark.

The hot gas in each cluster was slowed by a drag force, similar to air resistance, during the collision. In contrast, the dark matter was not slowed by the impact because it does not interact directly with itself or the gas except through gravity. Therefore, during the collision the dark matter clumps from the two clusters moved ahead of the hot gas, producing the separation of the dark and normal matter seen in the image. If hot gas was the most massive component in the clusters, as proposed by alternative theories of gravity, such an effect would not be seen. Instead, this result shows that dark matter is required.

Link: Image: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.
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