On Wednesday, an international team of scientists announced they had found the most convincing evidence yet that dark matter exists.
Dark matter makes up at least a quarter of our universe. It's the invisible stuff that holds our stars, galaxies, and clusters of galaxies together. The problem is, no one has ever been able to prove that it exists.
The latest results are not conclusive, but they provide better evidence than any previous experiments, MIT astrophysicist Samuel Ting said in a news conference. We are closer than ever to one of the secrets of the universe.
It all started in 1933 when Fritz Zwicky noticed something weird in a distant galaxy.
Zwicky, from the California Institute of Technology, noted a discrepancy between the mass of visible matter and the calculated mass of a galaxy cluster called the Cosizema cluster.
He calculated that the cluster had 400 times more mass than it should have had, based on what he saw with a telescope.
Zwicky also noticed that motion of the galaxies in the clusters was much too fast to be held together from the gravitational attraction created by visible matter alone.
The stars and galaxies would fly apart if there weren't some extra mass creating a gravitational effect that kept them together.
Zwicky theorized that there must be some invisible "dark matter" to explain his observations.
It took many many decades, however, for the world to warm up to Zwicky's theory. That's because dark matter is just that — dark. The mysterious substance does not emit or absorb light, or other forms of electromagnetic waves.
So finding concrete evidence of the elusive substance is incredibly difficult.
Although dark matter cannot be seen or touched, we can measure its gravitational effects.
Mass is measured by its gravitational effects on celestial bodies. The more massive something is, the stronger its gravitational pull. Gravity is the glue that holds our solar system, galaxies, and clusters of galaxies together.
Scientists know the mass of visible matter, like stars, dust, and gas, and that this mass would not create a strong enough gravitational attraction to keep stars and galaxies together. Thus, without the gravitational interactions created by some invisible mass, which we have named "dark matter," galaxies would fly apart as they whip around.
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