Thomas Griffiths on Dark Matter:

The Universe is still very much a mystery to us, read about an interesting discovery in 1934 that suggested there was more to the universe than what we can see.



Dark matter is a term used to describe matter that is undetectable. If dark matter is undetectable how did we discover it? In 1934 Fritz Zwicky tried to measure the amount of mass in a cluster of galaxies by measuring their brightness. Dark matter does not radiate enough light, if any, to have been included in this first measurement. So Fritz decided to use a different method, by observing the galaxies effect on the gases between them, and had entirely different results. The estimated mass of the galaxies was almost 400 times larger in the second measurement. This indirect evidence indicated that there was dark matter in our universe. Today scientists believe that dark matter makes up 83% of all matter. Ever since that historic discovery scientists have been trying to identify dark matter and have proposed several theories.

WIMPs:

Some believe that dark matter consists of massive particles called WIMPs (weakly interacting massive particles). These particles are proposed to rarely interact with other particles and millions of them may be passing through us every second.

Super Symmetry:

Super Symmetry is purely theoretical in that it hasn't been proven or disproved. Super symmetry is popular because it unifies gravity with the other three forces and explains quantum mechanics. The general idea of super symmetry is that every particle has a heavier superpartner that differ by 1/2 a unit of spin as well as an anti-particle. These superpartners are said to only interact with matter through gravity. Mass is inversly proportional to speed, since shadow particles are much heavier (have more mass) they must also be much slower. These superparticles or "sparticles" are one candidate for dark matter and may be contributing to the excess amount of gravity in our galaxy.

Neutrinos:

But scientists have discovered a weakly interacting particle called the neutrino. Neutrinos travel at close to the speed of light, are electrically neutral, and zoom across space, and even through you at this very moment, undisturbed. There are 3 different kinds of neutrinos: electron neutrinos, muon neutrinos, and tau neutrinos. Neutrinos (according to quantum mechanics) can fluctuate between these states. Another interesting fact about neutrinos is that they have spins anti-parallel to their momenta. Neutrinos are created through beta decay and a common source of Nuetrinos is our own sun. Since Neutrinos have mass they are a valid candidate for dark matter.

MACHOs:

The next candidates for dark matter are called MACHOs (massive compact halo objects). MACHOs consist of blackholes, nuetron stars, and the collapsed remains of medium-sized stars called dwarfs. MACHOs are detected through gravitational lensing.Gravity bends light so when a MACHO passes in front of a star the light is bent significantly allowing scientists to locate them.

Dwarfs:

There are three kinds of dwarfs: white, brown, and black. A white dwarf occurs when a medium sized star that does not have enough mass to go supernova. As stars near the end of their life they expand into a red giant. When the outer layers disperse and form planetary nebula the carbon and oxygen core remains which eventually forms a white dwarf. Since fusion can still occur in a white dwarf, it can still radiate light until it runs out of fuel and becomes a black dwarf. White dwarfs are known to spin extremely fast and are incredibly dense (comparable to the density of our sun) but only as large as a small planet like Earth. Brown Dwarfs are much less impressive. They have much lower temperatures, do not radiate much light, and have a lower density than white dwarfs. Brown Dwarfs are thought to be either the remains of a low-mass star or high-mass planets. Brown Dwarfs cannot fuse carbon but are known to fuse deuterium and lithium. Brown Dwarfs do actually emit just enough light to have a brownish tinge, hence the name "Brown Dwarf." Black Dwarfs are just white dwarfs that no longer emit any light. Dwarf stars do not collapse even further becoming a black hole because of electron degeneracy.

Neutron Stars:

Neutron Stars are the results of type 2 supernova which can also create black holes. Neutron Stars are so compact that a mere teaspoon weighs 5.5×10 to the 12th power kilograms. Neutron Stars have higher temperatures than white dwarfs and at birth can reach temperatures up to 10 to the 12th power kelvin. Neutron Stars, like white dwarfs, appear white. Thanks to conservation of angular momentum Neutron Stars spin extremely fast. A Neutron Star's gravity is so strong all the matter that it captures forms an accretion disc similar to those surrounding a black hole. Neutron Stars are so compact that there are no individual atoms and they are made entirely of neutrons. Magnetized Neutron stars are referred to as pulsars because they seem to blink on and off through a telescope.

Black Holes:

Black Holes occur when even
Pauli's exclusion principle cannot stop the core from collapsing on itself to form a singularity. Black Holes push physics to the limit and have mystified scientists for decades. A Black Hole rips matter apart and compresses it into a single point. Black Holes distort space-time so much that frame-dragging occurs. It has been proven that gravity slows time. Time slows down so much near a black hole that if you were an outside observer watching someone else dive in, you would never actually see them cross the event horizon. They call these "freaks of nature" Black Holes because not even light can escape their influence. This implies that their escape velocity is faster than the speed of light, which is supposedly the cosmic speed limit. Many scientists believe that if time-travel or wormholes are possible it is through a black hole. In a Large Hadron Collider scientists have been known to create mini-black holes which disappear almost instantly after they are created.

Dark Energy:

The Universe is expanding, we all know that, but not only is it expanding but it is expanding at an accelerated rate! You'd think that if gravity was the only force on a cosmic scale that the universe's expansion would be decelerating. Obviously there is some other force involved that is causing this. Scientists have called this mysterious force Dark Energy. We know almost nothing about it's properties or how it works, just that it exists everywhere. If Dark Energy is stronger than gravity then the universe will never stop expanding and eventually the only thing left in the universe would be Dark Matter. Today Dark Energy makes up 72% of the known universe while matter makes up only 28%.

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