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 quarter of our universe. It's the invisible stuff that holds our stars, galaxies, and clusters of galaxies together.
The problem is, so far, scientists can't definitivley prove that dark matter 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.
So while we still may not have directly found dark matter, we are closer than ever before.
It all started in 1933 when Fritz Zwicky noticed a discrepancy between the mass of visible matter and the calculated mass of a galaxy cluster.
Zwicky, from the California Institute of Technology, picked up on this inconsistency while observing a cluster of galaxies 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.
But that's not all. Beyond the issue that the cluster's mass did not match what could be observed from light, 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.
There must be something else there that is invisible to our detectors, he theorized. He called this missing mass "invisible matter" or "dark matter."
It took many many decades for the rest of the world to warm up to Zwicky's invisible dark matter theory, however.
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.
See the rest of the story at Business Insider