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When Swiss astronomer Fritz Zwicky caught the Coma galaxy cluster moving faster than its mass should allow in 1933, he came up with a novel theory: There must be some hidden mass that escaped his detection. He termed this mysterious substance dunkle Materie or dark matter. Now, after almost 100 years, scientists may have directly observed dark matter for the first time.
Dark matter has captured the imagination of astrophysicists for years. As research into the strange phenomenon increased, the indirect evidence it was real mounted, and dark matter moved from the fringes of physics to the mainstream. As technology improved, astrophysicists saw the effects of dark matter in the rotation of spiral galaxies, blamed it for peculiar gravitational lensing effects, and discovered its signature in the remnants of galactic collisions. Strikingly, estimates conclude our universe is made up of 27 percent dark matter and just 5 percent ordinary matter. That means dark matter outweighs “normal” matter by a factor of five to one.
Even though it seemingly pervades the heavens, we still haven’t been able to see it. Dark matter is “dark” because it doesn’t interact with electromagnetic forces. In other words, dark matter doesn’t reflect, absorb, or emit visible light or any other wavelength from the electromagnetic spectrum. That doesn’t just make it difficult to see, it makes it impossible.
Read more: “Have We Gotten Dark Matter All Wrong?”
So how do we detect the undetectable? Researchers hypothesize that dark matter is made up of “weakly interacting massive particles,” or WIMPs, that are about 500 times heavier than protons, but don’t really interact with other matter. They do (theoretically) interact with one another, and physicists believe that when they collide the annihilation of the two releases gamma ray photons, which we can detect.
Tomonori Totani, of the University of Tokyo, believes he’s detected gamma ray emissions from dark matter collisions for the first time. Totani pointed NASA’s Fermi Gamma-ray Space Telescope to areas where dark matter should be plentiful and published his findings recently in the Journal of Cosmology and Astroparticle Physics.
“We detected gamma rays with a photon energy of 20 gigaelectronvolts (or 20 billion electronvolts, an extremely large amount of energy) extending in a halolike structure toward the center of the Milky Way galaxy,” Totani said in a statement. “The gamma-ray emission component closely matches the shape expected from the dark matter halo.”
Totani’s research indicates both the intensity of the gamma ray emissions and their frequency match theoretical estimates of WIMP annihilation.
“If this is correct, to the extent of my knowledge, it would mark the first time humanity has ‘seen’ dark matter. And it turns out that dark matter is a new particle not included in the current standard model of particle physics. This signifies a major development in astronomy and physics,” Totani said.
Totani’s work will now have to be confirmed, but if it is, it’s more than just a major development. After almost 100 years, the evidence of things not seen may have finally surfaced. 
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Lead image: NASA/CXC/M. Weiss
