How Do We Find Dark Matter?

Physicists are on the hunt for dark matter, but how do they detect it?

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Scientists estimate that dark matter makes up to 85 percent of the universe. But we've never seen it or even know what it might look like. Dark matter has fascinated physicists since they first realized that there was more stuff in the universe than they could explain with their current theories. In 1933 Swiss astronomer Fritz Zwicky found some strange discrepancies in his measurements of galactic masses. He tried to measure the mass based on the speed of the galaxy's spinning, but he also tried to measure the mass based on the amount of visible light.

It took 30 years to find solid evidence that dark matter exists. Astronomer Vera Rubin discovered stronger evidence of what's called the galaxy rotation problem. It's mostly undetectable: it doesn't emit light or any kind of electromagnetic radiation. The only clue to it's existence is the gravitational effects on nearby objects. After adding up all the mass of all the stars in certain spiral galaxies, she found that they were spinning faster than they should be. Rubin concluded there must be some unknown stuff out there with enough mass to effect the spin of entire galaxies. The best evidence we have of dark matter comes from readings of the Bullet Cluster in 2006. Galaxy clusters are the most massive things we can see in the universe, mostly made up of hot gas, stars and dark matter. This particular cluster is actually two galaxies caught in the act of colliding. As they collided a shock wave spread through the cluster, in the shape of a bullet (hence it's name).

Because dark matter doesn't interact electromagnetically with anything, it's thought that it's made up of clouds of elementary particles dubbed WIMPS (Weakly Interacting Massive Particles). Since wimps don't interact electromagnetically how do we find them? Therein lies the problem. A recent study published in the journal Physical Review Letters researchers suggest a new approach: they believe that when two dark matter particles collide and annihilate they produce radiation, so they suggest looking for this radiation rather than the particles themselves.

Learn More:

NASA Finds Direct Proof of Dark Matter (NASA)
"Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies. The discovery, using NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter."

What Is Dark Energy? (NASA)
"More is unknown than is known. We know how much dark energy there is because we know how it affects the Universe's expansion."