The dark side of the universe

Most of the cosmos is invisible, but that doesn’t stop scientists from searching for it

By Stephen Ornes, 17:06 PM April 26, 2011

The ghostly blue clouds in the center of the Abell 1689 galaxy cluster show where Dan Coe and his team think dark matter is hiding. Abell 1689 is home to about 1,000 galaxies and trillions of stars. Credit: NASA, ESA, and Dan Coe (NASA JPL/Caltech and STScI)

If seeing is believing, then we shouldn’t believe in most of our universe.

We can see the sun, other stars and faraway objects that glow in the dark. With the right tools, we can even see things that would otherwise be invisible, like the air in the atmosphere or hot gas in distant galaxies.

Astronomer Carl Sagan liked to say, “We are made of star stuff.” He meant that everything we know — you and your dog, the Earth and moon — is made of the same kinds of atoms as glittering stars. Thes...

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