All About Dark Matter



So What is Dark Matter Anyways?

  • Invisible/Undetectable matter in the universe comprised of exotic, elementary particles that have yet to be identified or confirmed.
  • Believed to explain discrepancies in Kepler's law of gravitational orbit in galaxies.
  • Composed of various subatomic particles such as MACHO's, WIMP's, and neutrinos.

Can you find the dark matter in this body of stars?  Most scientists can't.
Can you find the dark matter in this body of stars? Most scientists can't.

Galaxies such as this one are believed to contain billions of particles of dark matter!
Galaxies such as this one are believed to contain billions of particles of dark matter!




How did the idea of dark matter form?

  • Hypothesized by philosophers for many years that some invisible form of matter existed in our universe.
  • Scientists calculating the mass of galaxies using Kepler's Law found discrepancies in most galaxies observed as the mass believed to exist was too small to account for the observed velocity of galaxies and celestial bodies.
  • The discrepancies in Kepler's Law led scientists to conclude that some form of undetectable matter exists out in the universe.

Scientists such as this one now believe they are on track to make a groundbreaking discovery about our universe.
Scientists such as this one now believe they are on track to make a groundbreaking discovery about our universe.
Johannes Kepler would be proud to know that scientists today still rely on his law to make new discoveries about our universe.
Johannes Kepler would be proud to know that scientists today still rely on his law to make new discoveries about our universe.




Presence of Dark Matter in the Universe

Experts hypothesize that dark matter initially made up a large portion of matter in the universe, but today most substance in the universe is thought to be comprised of dark energy
Experts hypothesize that dark matter initially made up a large portion of matter in the universe, but today most substance in the universe is thought to be comprised of dark energy


What types of particles compose dark matter?

  • Massively Compact Halo Objects (MACHO's): any body consisting of baryonic matter, which emits little to no radiation and drifts through interstellar space unassociated with any solar system; initially thought to comprise the majority of existing dark matter, but later concluded to only comprise a minuscule portion of the total dark matter in the universe as scientists have shown that only an insignificant amount of baryonic matter can possibly exist in the universe through interpretation of the Big Bang Theory as well as analysis of the cosmic microwave background and the bayron acoustic oscillations. Includes relatively normal objects such as brown dwarfs, old white dwarfs, and black holes. MACHO's also are often found clumped together and travel in blocks across space.

Black holes such as the one shown above are one of the many objects scientists classify as a MACHO
Black holes such as the one shown above are one of the many objects scientists classify as a MACHO


  • Weakly Interacting Massive Particles (WIMP's): particles that interact through the weak force and gravity; cannot be seen directly due to the fact that they do not interact with electromagnetism and because they do not interact with the strong nuclear force, leading scientists to consider this undetectable form of matter as one of the primary composites of dark matter; much slower and more massive than neutrinos. They are spread out evenly among the galaxies they are found in in accordance to supersymmetry.

Here WIMP's can be seen evenly spread out across a galaxy in supersymmetry.
Here WIMP's can be seen evenly spread out across a galaxy in supersymmetry.

  • Neutrinos: elementary particle in nature that moves close to the speed of light across space and pass through ordinary matter undetected. They are created by the radioactive decay or nuclear reactions that take place in stars or when cosmic rays hit atoms. Studies show that this particle is electrically neutral and possess some qualities of the average electron (minus the charge) or a neutron. The difference between a neutron and a neutrino lie in the fact that neutrinos contain only a mere fraction of mass that the average neutron possesses, often making the particle difficult to detect. This difficulty in detecting neutrinos has led scientists to believe that neutrinos may also comprise some portion of the existing dark matter in the universe.

Computer imagery shown above depicts theoretical neutrinos moving at a pace relative to the speed of light
Computer imagery shown above depicts theoretical neutrinos moving at a pace relative to the speed of light


  • In addition, dark matter is hypothesized to behave like a perfect fluid as it has no internal resistance or viscosity. This means that dark matter particles should not interact with each other through any force other than gravity, which results in dark matter traveling past each other without bumping or colliding.


What theories of dark matter exists?

  • Cold dark matter: currently the most popularly held theory concerning dark matter and its relation to the Big Bang; states that the majority of dark matter is comprised solely of weakly interacting massive particles (WIMP's). Scientists who support this theory believe that dark matter moves at relatively normal speeds compared to other celestial bodies in the universe. Believed to be the most solid theory for the support of dark matter as it effectively explains galaxy and galaxy cluster formation.

  • Warm dark matter: Theory stating that dark matter consists of particles moving at relatively faster speeds, but not quite at the speed of light. Does not adequately explain the formation of galaxies following the Big Bang due to the fact that warm dark matter would move too fast to be bound into galaxies. No particles have been discovered thus far to support the theory of warm dark matter and this theory may prove to be incorrect as time goes on and more research is performed.

  • Hot dark matter: Theory stating that dark matter consists of particles moving at ultra-relativistic speeds that reach and in some cases surpass the speed of light. Neutrinos, which have already been discovered by scientists today, are believed to support the theory for hot dark matter as they are particles which often travel at the speed of light. Like warm dark matter, hot dark matter cannot explain the formation of galaxies and galaxy clusters

  • Mixed dark matter: Model of dark matter rendered obsolete many years ago. States that a specific mass ratio exists in the composition of dark matter with 80% containing cold dark matter and 20% containing hot dark matter. Made invalid in the 1990's with the discovery of dark energy in the universe.


What evidence do scientists have in support of dark matter thus far?

  • Scientists are currently undergoing various experiments to verify the existence of many proposed particles that are hypothesized to compose dark matter.

  • Massively compact halo objects (MACHO's), which were once believed to comprise the majority of dark matter in the universe, are now postulated to contain a mere fraction of the total amount of dark matter in the universe as scientists have concluded that not nearly enough MACHO's exist in the universe to cover the entirety of mathematical discrepancies in the calculations of Kepler's law.

  • Weakly Interacting Massive Particles (WIMP's) are currently the most widely held candidate for the majority of dark matter. Studies performed by the IceCube Neutrino Observatory in Antarctica have yielded data which further suggests the conclusion that WIMP's are truly the largest candidate for dark matter in the universe.

  • Neutrinos are the only particle thought to comprise dark matter that has been confirmed in both natural observations and clinical experiments; however, most scientists believe that neutrinos cannot effectively explain the role of dark matter in the universe as current theory holds it, leading many to rule it out as a leading composite of dark matter in the universe



Why do scientists care about dark matter?

  • In the past, breakthrough discoveries, such as the potential confirmation of the wide scale presence of dark matter in the universe, have led others to utilize said discoveries to benefit society here on Earth.

  • The discovery or rejection of dark matter in the universe will bring mankind one step closer to fully realizing the structure and contents of our universe

  • It will be many years or even decades of extensive research, data collection, and analysis before scientists can ultimately come to any conclusion on whether dark matter actually exists or not in the universe.

Dark matter may prove one day to be as important of a discovery as Thomas Edison's development of the lightbulb!
Dark matter may prove one day to be as important of a discovery as Thomas Edison's development of the lightbulb!



For more information on dark matter, check out:

Your local library!
Wikipedia - Dark Matter
PBS - The Dark Matter Mystery
PBS - Dark Matter
Youtube - The Dark Matter Mystery: Stars are Moving Too Fast