We have basically no idea what dark matter is, even though it might make up most of the cosmos. But scientists have figured out where it is, and they're mapping it in portions of the visible night sky. Above, you can see the first piece of their map: It covers just 3 percent of what their data will eventually yield, but it covers around 2 million galaxies. The red and yellow regions are most dense with dark matter, and the dots represent clusters of galaxies.
Dark matter is a tricky thing. It's much more common in the universe than the matter we understand, but cosmologists have a hard time pinning it down. Because it warps the space-time around it, bending light from surrounding galaxies in a way we can observe with telescopes, we're able to get a sense of where it's lurking -- even though we have very little idea of what it's doing there.
The map, which was presented Monday at the meeting of the American Physical Society, seems to confirm prevalent theories of how dark matter helps shape the cosmos. Scientists believe that galaxies should be more likely to form where dark matter is most concentrated, because they create strong gravity. Sure enough, the galaxies seem to form large clusters in the regions of space dense with dark matter, and blue-tinted voids attract fewer stellar neighborhoods.
"Our analysis so far is in line with what the current picture of the universe predicts," researcher Chihway Chang of ETH Zurich said in a statement. "Zooming into the maps, we have measured how dark matter envelops galaxies of different types and how together they evolve over cosmic time. We are eager to use the new data coming in to make much stricter tests of theoretical models."
The project, part of the Dark Energy Survey, includes more than 300 scientists from around the world. They're using the Dark Energy Camera, a 750 megapixel powerhouse mounted on the National Optical Astronomy Observatory's Blanco telescope in Chile. The survey is set to run through 2018, by which time the researchers hope to have created maps at this resolution for 1/8th of the visible night sky -- 30 times what this first map shows. With such a detailed picture of dark matter, the cosmologists hope to learn more about dark energy: the stuff that's keeping the stars apart, making our universe expand faster and faster instead of being slowed down by gravity.
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