Many scientists believe that invisible matter -- dark matter -- enshrouds the edges of galaxies.

In the 1970s, astronomer Vera Rubin started a scientific revolution with her discovery that stars at the edge of galaxies rotate faster than expected. Rubin's startling discovery implied that galaxies are embedded in immense halos of invisible, or Dark, matter.

An early hypothesis was that undetected planets accounted for this unseen matter. But astronomer Debra Fischer, who has spent years tracking planets outside of our solar system, says that these planets aren't enough.

Scientists now believe that not only is most of the missing matter probably not the stuff that stars and planets are made of — it's probably not the stuff that anything we know is made of.

In mines from northern England to the Appenine mountains of Italy to northern Minnesota, astronomers are digging deep in their hunt for Dark Matter. They're hoping to find Weakly Interacting Massive Particles, or WIMPs, never-before-seen particles that no one's sure even exist. Going underground keeps cosmic rays from interfering with their detectors.

As a young Astronomer, Vera Rubin discovered possible evidence for dark matter.

But astronomers aren't the only ones on the hunt. In Switzerland, physicists are eagerly awaiting completion of what will be the world's most powerful particle accelerator. There, they will smash particles in an effort to create Dark Matter. In the wreckage of these collisions, scientists hope to find supersymmetric particles, the essence of Dark Matter.

So far, the closest we've gotten to Dark Matter has been through the cameras of NASA's WMAP spacecraft. WMAP has provided the first detailed images of the oldest light in the universe, left over from the Big Bang. In the pattern of cosmic ripples left as the Big Bang cooled, WMAP scientists can see direct evidence for Dark Matter — which may outweigh normal, visible matter by six times or more.

Astronomers believe that Dark Matter was essential to the formation of galaxies. There wasn't enough gravity in visible matter to coalesce and make stars, so they think Dark Matter held the normal matter together and allowed it to concentrate, cool and then make stars.

Though Dark Matter's gravitational tug was indispensable to the birth of our universe, from the start it's been opposed by an anti-gravity force that might have overwhelmed it — had conditions been right — and blown the infant universe apart.

For more on this topic, see the web feature:
Eyes on the Skies