what is dark matter

Next to dark energy, the second largest component of the universe is dark matter. You can’t see it directly. However, we can observe dark matter’s effects from its interaction with the rest of the universe through its gravity. The truth is, we understand little of what Dark Matter is, and more of what it is not.

What do we know so far?

It is Dark

Dark matter cannot be seen directly and it radiates no light, so it can’t be stars or planets.

Cannot be detectable

It’s too dense and small to absorb or emit enough radiation and is thus undetectable by current imaging technology.

It is not clouds of normal matter

If dark matter was normal matter particles called baryons, it would be detected, using reflected light. However, it is undetectable, so it is not baryons.

It is not antimatter

Antimatter wipes out matter on contact and produces gamma rays, therefore Astronomers do not detect antimatter in dark matter.

It is not a black hole

Light bends with the gravity lenses of black holes, however, there have not been enough lensing events to account for the amount of dark matter that exists.

Who first discovered dark matter?

Jacobus Kapteyn was the first man to suggest the existence of dark matter in 1922 while studying stellar velocities.

Swiss astrophysicist Fritz Zwicky inferred the existence of dark matter during his work on galactic clusters in 1933.

In 1939, American astronomer Horace Badcock reported on the presence of dark matter, because of information gleaned from his measurements of galaxy rotation curves.

The late American astronomer Vera Rubin teamed up with instrument maker Kent Ford in the 1960’s and 1970’s, and together they used their new spectrograph to measure the velocity curves of spiral galaxies. They found that most of them contain six times as much dark matter as visible matter.

How are we searching Dark Matter?

Particle colliders

  • Large Hadron Collider – the world’s largest single machine designed to test various theories of particle physics.

Cosmology instruments

  • WMAP – Spacecraft that measured temperatures of the cosmic microwave background.
  • Planck – NASA-ESA space observatory that mapped the universe, thus revealing the oldest lights which had traveled billions of years.

Direct detection experiments

  • CDMS – At Soudan Mine in Minnesota.
  • LUX – Large Underground Xenon experiment at Sanford underground laboratory in South Dakota.
  • ArDM- At Canfranc underground laboratory in Spain.
  • XENON – Deep underground at Italian Gran Sasso laboratory.

Indirect detection experiments

  • Gamma-ray detectors- Fermi Space Telescope, ground-based Cherenkov Telescope Array.
  • Neutrino telescopes – IceCube Neutrino observatory, Antares telescope.
  • Antimatter detectors – Pamela, AMS-02, other X-ray and radio facilities.

Why do we care about Dark Matter?

The Higgs boson and dark matter might be connected. Both investigations are about the ways subatomic particles interact, and what the fundamental structure of the universe looks like. A better understanding of subatomic particles, therefore, is essential to making modern theoretical physics make sense.

Experts like Neil deGrasse Tyson believe that if dark matter makes up around 25 percent of the known universe, dark energy probably makes up about 70 percent of the known universe. Because of this, dark energy may be the reason the universe seems to be expanding.

Dark energy and dark matter are intimately connected.

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