Molecular Hydrogen Discovery Aids Researchers

By Katy Human
Daily Camera StaffWriter
Thursday, January 13, 2000

This edge-on view of the nearby galaxy NGC 891 clearly shows the dark layers of interstellar gas clouds from which new stars are constantly forming

A University of Colorado astrophysicist's discovery could help researchers better understand the dark clouds in space where stars are born.

For the last six months, Mike Shull and his colleagues have found molecular hydrogen almost everywhere they've looked in the Milky Way galaxy. Shull presented the results of his explorations in a talk Wednesday at the American Astronomical Society's annual meeting in Atlanta.

Using an instrument built at CU and launched into space last summer, Shull and his colleagues have been probing the galaxy for evidence of molecular hydrogen and other gases.

Molecular hydrogen, composed of two hydrogen atoms, is important because it fuels starbirth, Shull said.

Stars form in dark, cold regions of space called molecular clouds, which scientists have long assumed are packed with molecular hydrogen. Gravity and shock waves from celestial objects and events compress the material, which can eventually collapse to form a star.

No one suspected there'd be quite so much of the stuff out there.

"We see uncanny amounts of molecular hydrogen absorption," Shull said. "We saw it 90 percent of the time."

Frank Shu, an astrophysicist at the University of California at Berkeley, hadn't yet heard of Shull's new research. He said the discovery of more molecular hydrogen than expected could help solve a puzzle that has long troubled physicists studying star formation.

"One problem that has existed ever since molecular clouds were discovered is that ... the rate of star formation is alarmingly high compared to the amount of molecular material believed to be there," he said.

According to one calculation, based on previous assumptions of the amount of molecular hydrogen in the galaxy, all the gas would be used up in 250 million years.

"But the galaxy is maybe 10, 11 billion years old," Shu said. "That's off by a factor of 50."

Because stars die as well as form, and star death can send material back into the galaxy, astrophysicists might be off only by a factor of 10.

"That's still embarrassing," Shu admitted.

"Finding more gas would only, of course, help."

He and Shull cited other reasons to be intrigued with the results. According to conventional thought, molecular hydrogen forms only in relatively "shielded" regions in space. "Harsh environments break down molecular hydrogen," Shull said.

"It should not exist, yet somehow it finds a way to form. That means we have to figure out a mechanism for making this hydrogen form more readily in harsh environments."