Dark Matter's Origins
Matter is all around you, made up of atoms and molecules and they all interact with each other, even out in space. This matter can be described as baryonic. However, back in 1933, Fritz Zwicky noticed galaxies moving in the Coma cluster with speeds much greater than expected. The sum of the observed individual galaxy masses was much too light, implying that they should be flying off into space despite their observed behavior. What was missing?
Zwicky determined that there must be some other form of matter that we cannot see, what he called "missing matter," to account for the difference in speed. Thus, dark matter was discovered. However, like many of his other discoveries, scientists of his time did not agree with his results. They did not fully understand how large clusters of galaxies interacted at that time and dismissed the problem. Despite this backlash, many of his ideas have now been proven to be true. However, it wasn't until 1975 that Vera Rubin noticed the same effect on stars rotating around their galaxy's center, bringing the idea of dark matter back to light. This conundrum is shown in the figure.
Fritz Zwicky, the Father of dark matter
Vera Rubin confirmed Zwicky's missing matter in 1975
This graph shows how the expected speeds of stars rotating around their galaxy's center do not match the values measured, implying that there should be more matter, a lot more matter, than we can see.
Astrophysicist Neil deGrasse Tyson explains the conundrum of dark matter in under 2 minutes
Our Understanding Today
Dark matter is another type of particle, some form of non-baryonic matter very different than anything we've ever encountered or interacted with. With this new understanding of the universe, scientists discovered that particles and atoms like we understand and can interact with make up only about 5% of the matter and energy we have recorded in the universe. The vast majority of the mass of the universe is actually made up of this unknown particle that we call dark matter.
Immediately after the Big Bang, everything was extremely hot and expanding outward at great speeds. At this time, dark matter appears to have interacted with baryonic matter, photons, and waves that allowed galaxies, clusters of galaxies, and everything in the universe to form in the manner that it did. The universe could not have formed the way it did, without the aid of dark matter. Since then the universe has cooled with expansion; the dark matter continues to interact with regular matter only through gravity. See the pie graphs for more information.
Today, approximately 95% of the universe is what we call the dark universe, made up of dark matter and dark energy. Only about 5% is ordinary matter like stars and planets.
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