Astrophysicists at Virginia Tech are not star-gazers. They are among very few scientists looking at the warm gas that makes up 25 percent of the material between the 100 billion stars in our galaxy. Their results impact our understanding of the workings of our galaxy and the origin of our universe.

The so-called "warm interstellar medium" is a plasma with a temperature of 10,000 degrees Kelvin. "At that temperature it glows, somewhat like the gas in a fluorescent light," says John Simonetti, one of the faculty members in the astrophysics group, which also includes graduate and undergraduate students.

He explains that most of the gas in the universe is hydrogen. "If you put hydrogen gas in a glass tube and run a current through it, it will emit specific wavelengths. We are observing interstellar hydrogen's brightest emission line, or wavelength - the hydrogen-alpha line in the red part of the visible spectrum."

Hydrogen atoms emit light at this wavelength when they recombine after having been broken apart by, for example, the ionizing radiation from stars, says Dr. Simonetti.

The researchers are using Virginia Tech's Spectral Line Imaging Camera (SLIC), to conduct a systematic survey of much of the northern hemisphere, complemented by the Wisconsin H-alpha mapper (WHAM) survey of the northern sky and other's efforts in the southern hemisphere.

SLIC is specially designed for obtaining sensitive, arcminute-resolution, 10-degree wide images of our galaxy's warm interstellar gas. With it, researchers are capturing dramatic images of interstellar phenomena.

Simonetti and physics professor Brian Dennison and their students began to explore the interstellar medium (ISM) in 1994, after building an observatory on a rural mountainside outside of Blacksburg, Va., at the Miles C. Horton, Sr., Research Center. The Horton Foundation helped build the Martin Observatory -- named for Miles Horton, Jr.'s favorite grade-school teacher -- and the foundation, along with the National Science Foundation, has funded the research effort.

Cold gas has been well mapped by radio telescopes, but the volatile warm gas has not. "We are specifically interested in the fine-scale structure of the warm interstellar gas and how it is physically related to the other components of the interstellar medium, such as the cold gas," Dr. Simonetti says. In just a few years, the researchers have covered a major fraction of the northern sky obtaining images that capture both very faint and bright structures, thanks to their sophisticated instruments, making it possible to compare their maps with observations of the other components of the interstellar medium obtained through X-ray, radio, and infrared telescopes. "Only by collecting together these diverse sources of information can astronomers obtain a complete picture of the dymanic processes that are occurring within our galaxy," says Dr. Simonetti.

"The interstellar gas is churned up all the time by supernovae and by wind from the stars." Simonetti points out that we can see a local effect of the wind from our sun when we see the tail of a comet pointing away from the sun.

When a massive, hot star goes supernova a bubble is created around the star as interstellar gas is pushed away by the shock wave from the explosion. The material pushed ahead of the shock forms a "shell" or even a "supershell" bounding the bubble. Theoretically, a bubble may break out of the galactic disk of gas and therefore form a "chimney" through which hot gas can vent out of the disk. One of the Virginia Tech group's early discoveries was a supershell associated with the W4 star-forming region -- "a cloud of gas where stars form, somewhat like the condensation of raindrops in a cloud in our atmosphere," says Simonetti.

The results of the Virginia Tech astrophysics group's H-alpha program have also been important in studying the irregularities in the cosmic microwave background radiation, the observable remnant "fireball" of the big bang origin of the universe.

The gas that filled the universe after the big bang was not smooth. It had irregularities -- regions of slightly greater and slightly lesser density that were the seeds necessary to form galaxies and clusters of galaxies. That was the theory, anyway — unproved until NASA's COBE satellite found the first large-scale irregularities in the cosmic microwave background.

Now, ground-based radio telescopes are searching for, and in some cases, apparently finding smaller scale irregularities. Measuring the relative strength of the small and large scale irregularities is a key to discriminating among a variety of models of the big bang and of galaxy cluster formation.

"But they couldn't tell for sure whether they were observing small scale irregularities in the cosmic microwave background, or just irregularities in the foreground microwave-emitting galactic plasma that can mimic the irregularities in the background radiation," says Simonetti. Now, with SLIC, "We can determine and eliminate the foreground, galactic irregularities."

Dr. Simonetti maintains a web page with additional information and links to the Virginia Tech group's findings.