StarDate: May 5, 2009

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The space between galaxies looks empty. And by everyday standards, it is -- a vacuum that's far emptier than anything that scientists can create in the laboratory. Even so, all those long, lonely parsecs aren't completely empty. They contain giant clouds of gas, plus vast amounts of dark matter.

This month, a balloon is scheduled to loft a telescope into the stratosphere to study the material between galaxies. It'll map long filaments of gas, and shed some light on dark matter.

The experiment is known as Fireball. It'll launch from near Fort Sumner, New Mexico, and have most of a night to look at the sky.

Fireball consists of a one-meter telescope and an ultraviolet detector. Earth's atmosphere absorbs ultraviolet energy, so the only way to see the ultraviolet sky is to lift a telescope above the atmosphere. The balloon will carry Fireball about 25 miles up. At that altitude, the air is so thin that some ultraviolet wavelengths can get through.

Fireball will map the faint glow from filaments of gas that can span millions of light-years. Scientists will use the observations to "weigh" the amount of gas between galaxies.

The way the gas is distributed will provide clues to the presence of dark matter -- matter that produces no energy, but exerts a gravitational pull on the "normal" matter around it.

Fireball's observations will help astronomers fill in the emptiness between the galaxies.

We'll talk about another balloon mission tomorrow.

Script by Damond Benningfield, Copyright 2009

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