Sunday, July 12, 2015

A Simple Explanation of Dark Matter

Up until recently, it was thought that there was only one kind of matter in the universe. Sure, it came in many forms (liquid, solid, gaseous, and plasma), but everyone agreed that matter consisted of atoms that behaved in predictable ways. For instance, when you shine a light on matter, you can see it.

Then Dark Matter was discovered. Dark Matter doesn't interact with ordinary matter or light. It can't be seen directly. Its presence is inferred by its visible gravitational influences across a very large scale (light bends to go around a gigantic, invisible, heavy, object). 

It turns out that ordinary matter only makes up 4.9 percent of the total matter in the universe. Scientists now believe that Dark Matter accounts for 26.8 percent of the total. In other words, there is about five times as much invisible, Dark Matter around us as ordinary matter.

The existence of Dark Matter was hypothesized back in the 1930s to answer the question: given the speed that galaxies rotate, why don't their stars go flying off into space? What holds galaxies together? The calculated mass of the galaxies' stars was nowhere near heavy enough to hold a galaxy together. Something extremely heavy--massive--had to be sitting right in the middle of every galaxy, using its gravity to hold the rotating stars in place.

Here's what NASA says about the image above:


This Hubble Space Telescope composite image shows a ghostly "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 is superimposed on a Hubble image of the cluster. The ring is one of the strongest pieces of evidence to date for the existence of dark matter, an unknown substance that pervades the universe.
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 mapping also shows how dark matter is distributed in the cluster.
Astronomers suggest that the dark-matter ring was produced from a collision between two gigantic clusters.
Dark matter makes up the bulk of the universe's material and is believed to make up the underlying structure of the cosmos.
The Hubble observations were taken in November 2004 by the Advanced Camera for Surveys (ACS). Thanks to the exquisite resolution of the ACS, astronomers saw the detailed cobweb tracery of gravitational lensing in the cluster.
Object Names: CL0024+17, ZwCl 0024+1652
Image Type: Astronomical
Credit: NASAESA, M.J. Jee and H. Ford (Johns Hopkins University)
Readers of the Simple Explanation blog no doubt recognize the lovely torus shape assumed by the Dark Matter "ring." The Simple Explanation's cosmology predicts there will be a ring shape associated with every galaxy's center, as well as a ring shape around just about every other object in the universe. The Simple Explanation suggests that the torus shapes predate and are the cause of the galaxies' formation, not vice versa as most astronomers theorize.

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