Dark Matter Hits the Average Human Once a Minute?

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PostSat Apr 28, 2012 6:02 pm » by Mozi!!a


Particles called WIMPs strike us more often than thought, study says.
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The average human body gets hit by a particle of dark matter about once a minute, according to new calculations based on several dark matter detection efforts.

Dark matter is an invisible form of material that's thought to exist because scientists have observed its apparent gravitational effects on galaxies and galaxy clusters. Scientists estimate that the mysterious substance makes up almost 80 percent of the matter in the universe.

So far no one's been able to pinpoint the particles that make up dark matter. But a leading candidate is a theoretical group known as Weakly Interacting Massive Particles, or WIMPs.

As the name implies, these hypothetical particles would have only a weak effect on regular, or baryonic, matter—they typically zip straight through most of the stuff in the universe, including people.

(Related: "Dark Matter Is Missing in Sun's Neighborhood?")

But WIMPs of certain masses can collide with atomic nuclei on occasion—and now it appears such collisions might happen more often than previously thought.

"Before we did this work, I thought a WIMP collided with one of your nuclei once in your lifetime," said Katherine Freese, a professor with the Michigan Center for Theoretical Physics at the University of Michigan.

"Turns out it's more likely to be one a minute."

WIMPy Collisions

According to theory, WIMPs were created at the dawn of the universe, just like other forms of matter.

Although WIMPs don't interact much with normal matter, if two of the particles strike each other, they annihilate—all their mass turns into energy.

"As the universe [expanded and] cooled, [WIMPs] spread so far apart they no longer annihilated and just stuck around," said study co-author Christopher Savage, a postdoctoral researcher with the Oskar Klein Centre at Stockholm University in Sweden.

Models suggest that today billions of WIMPs are streaming through Earth and its inhabitants every second.

Some experiments designed to detect WIMPs are based on the expected probability of a WIMP hitting a particular type of material—such as germanium crystals—and the amount of energy that should be released by the collision.

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http://news.nationalgeographic.com/news ... e-science/

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