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Dark matter is named so because we cannot directly observe this matter with the instruments we have available today. We know it does exist because we can measure the gravitational effects of galaxies by applying Newton’s laws.
The idea of dark matter was first conceived in 1933 by a Swiss astrophysicist by the name of Fritz Zwicky, while working at the California Institute of Technology. Zwicky noticed by observing the Coma galaxy cluster (which has about 1000 observable galaxies), the galaxies at the outer edges of the cluster revolved about the cluster much faster than they should, by calculating the observable mass in the cluster. Zwicky concluded that in the cluster there should be 400 times more mass based on the laws of gravity, as we know it. This invisible mass was not only holding these galaxies together but would also explain the faster than expected rotational speeds at the outer edges of the cluster that he was observing. The problem was, how do you explain this unaccounted mass that can not be seen? Hence the name “Dark Matter". Here are some facts and theoretical facts about Dark Matter.
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- Mass: Dark matter has up to ten times more mass than dust, stars, and gas that is visible in galaxies observed and measured. This conclusion has been made because there is just not enough Baryronic matter (observable matter) visible that would account for the gravity needed to hold a galaxy together.
- Universe: Dark matter makes up an estimated 22 percent of our universe based on current indirect observations.
- Bullet Cluster Galaxy: This is the remnants of two galaxies that collided. The uniform distribution of stars is not unusual but there are clumps of gas that are separated into two parts. This shows that gravity is caused by something else (dark matter) keeping these two clouds separate and not merging uniformly as would be expected.
- Indirect Observation: Although we cannot see dark matter we can observe the effects it has on matter. For example: we can see the Bullet Cluster galaxy's gas being separated by gravity from an unseen form of matter.
- Spiral Galaxies: A spiral galaxy is roughly formed shaped like a fried egg. The big bulge where the yolk is, is the middle with while the remainder of the galaxy is flat, like the white part of the egg. According to Newtonian physics, stars closest to the center of the galaxy (yolk) will have a faster orbit than stars in the edge (the white part). Our observations show the stars at the outer edges are moving faster than the stars orbiting near the center of spiral galaxies, which implies that they are interacting with the gravity of unseen matter.
- Percentages: We can currently observe that Baryronic matter that makes up 4 percent of our universe. This means that 96 percent of the matter that makes up our universe is currently not visible to us by direct observation
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Theories of Dark Matter
- Brownian Motion: Can be described as matter acting not too differently from a drunken sailor's wandering path. Recently, Brownian motion has been applied on a galactic scale to show theoretical models of how dark matter could cluster into “Dark Satellite Galaxies". These could exist and cause some of the indirect effects of gravity we can observe on Baryronic matter.
- Dark Matter May not Exist: Some scientists believe that our standard model of the universe is wrong and we need to revise how gravity works. With modifications to our current laws of gravity it may eliminate the need of Dark Matter.
- M-Theory (String Theory): Some cosmologists make a case that we can eliminate the dark matter mystery by using M-Theory’s multi-dimensional aspects to explain that the gravitational effects are from other dimensions we cannot observe.
- Hadron Collider: Once the Hadron Collider is up and running, we may be able to detect dark matter. There is a theoretical particle, named a WIMP (Weakly Interacting Massive Particle) that may play a part in the missing mass of the universe. A WIMP could be detected by the observation of missing momentum and energy from a collision in the collider.
- Fermi Space Telescope: There are hopes that the Fermi Space Telescope might detect a gamma wave event produced by the collision of WIMP supersymmetric particle with a WIMP antiparticle. The hope is to find out how much dark matter may be composed of WIMPS.
- Galaxy Formation: There are theories that dark matter clusters or even dark matter galaxies may have been crucial to the formation our Baryronic galaxies. The theory is the gravity from these clusters could have pulled the matter together to give birth to the galaxies we can directly observe and also live in.
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1. The high energy physics lab in the Soudan Mine in Minnesota, run by the University of Minnesota for the Cryogenic Dark matter Search, is taking an approach to detect heat that could be generated when a WIMP passes through silicon crystals and ultracold germanium.
2. Neutrinos were also a form of matter that was hypothesized in 1930. The particle is unseen and constantly passes through us, Earth, and space at speeds close to the speed of light. Direct evidence of neutrinos was finally discovered 26 years later in 1956. Moral of the story - don’t count dark matter out yet.
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