Edge-on view of the nearby galaxy, NGC 891, taken by
astronomers at the University of Wisconsin (WIYN Telescope).
This image clearly shows the dark layers of interstellar gas
clouds from which new stars are constantly forming.

Full size image available through contact

Information streaming back from a new NASA satellite indicates that molecular hydrogen, the primary ingredient for star and planet formation, is found nearly everywhere in the Milky Way Galaxy, according to a University of Colorado at Boulder study.

As the most abundant element in the universe, hydrogen takes the form of molecular hydrogen, or H2, as it condenses into dark, star-forming clouds in interstellar space, said CU-Boulder Professor Michael Shull, chair of the astrophysical and planetary sciences department. Molecular hydrogen largely was hidden from view before the June 1999 launch of NASA&#039s Far Ultraviolet Spectroscopic Explorer satellite, or FUSE, which probes the far UV radiation portion of the light spectrum invisible to the Hubble Space Telescope.

“FUSE has provided us the eyes to see molecular hydrogen with a sensitivity thousands of times greater than its predecessor satellite, Copernicus, that flew in the 1970s,” said Shull, a co-investigator on the FUSE project. “We also used FUSE to detect molecular hydrogen in other galaxies like the Large and Small Magellanic Clouds, suggesting star formation proceeds in similar fashion in much different space environments.”

Shull presented the new FUSE results at a press briefing held at the American Astronomical Society&#039s 195th national meeting in Atlanta Jan. 11 to Jan. 15. Other CU-Boulder researchers involved in the molecular hydrogen study were Professor Ted Snow, doctoral student Jason Tumlinson and postdoctoral researchers Mark Giroux and Brian Rachford.

Dark molecular clouds are extremely cold, dipping below minus 300 degrees Fahrenheit, said Shull. The interstellar clouds pull together individual hydrogen atoms to form H2 molecules and soon collapse under their own gravity to begin the star formation process.

“The clouds are the star nurseries from which new stars and planetary systems form,” said Shull. Stars forming in clusters in the densest portion of the interstellar clouds are undoubtedly accompanied by newly forming planets, although scientists do not yet understand the details of the process and how often planets are formed, he said.

Stars form most rapidly in the dense cores of interstellar clouds, said Shull. The young, massive stars then blow away remaining material with strong stellar winds and seed the galaxy with new star-forming material.

Giant, exploding stars known as supernovae likely created the halo of violently heated hydrogen gas enshrouding the Milky Way, said Shull. But how the hot gas is assembled into dark molecular clouds, completing the stellar life cycle, is still a mystery.

Designed and built by CU-Boulder, this $9 million
spectrograph flying on the FUSE satellite is helping
scientists better understand the life cycles of stars.
Photo courtesy CU-Boulder.

Full size image available through contact

“FUSE has provided astronomers with a key means of probing the life cycles of stars, Shull said. “Understanding star formation in the Milky Way and nearby galaxies gives astronomers clues about how the first stars formed 10 to 12 billion years ago.”

FUSE detects gases and determines their composition, distance and velocity by pointing at distant, bright targets such as quasars. The light absorbed by the gas clouds in between provides “optical fingerprints” that reveal the contents of the gas.

Four FUSE telescopes collect and funnel UV light into a $9 million spectrograph designed and built by CU-Boulder that breaks down the light like sunbeams passing through a prism, Shull said. The international mission involves 19 science team members from the United States, France and Canada, including five from CU-Boulder.

FUSE is a powerful telescope used to study far UV light emanating from distant stars, galaxies, quasars and interstellar gas and dust. The telescope can view light from sources up to 10 billion light-years away, while the Copernicus satellite could view only the nearest 1,000 light-years. One light-year is about six trillion miles.

Mission scientists also are using FUSE to learn more about the evolution of the early universe, including determining the amounts of primordial gases in the vast space between galaxies to understand the origin and evolution of our own galaxy, he said.

By measuring the ratio of hydrogen to deuterium — a heavy form of hydrogen thought to have been manufactured only during the Big Bang — FUSE scientists hope to better understand star evolution and infer primordial conditions in the universe during its first few billion years of existence, Shull said.

The FUSE spectrograph is a progenitor of the Cosmic Origins Spectrograph, a $40 million instrument selected in August 1997 by NASA for insertion on the Hubble Space Telescope. It is being designed by CU-Boulder&#039s Center for Astrophysics and Space Astronomy and built jointly by CU and Ball Aerospace Systems Group of Boulder. The spectrograph is slated for installation on Hubble in 2003.

The FUSE spectrograph was assembled at CASA’s Astrophysics Research Laboratory in the CU Research Park under the direction of Professor James Green. The FUSE effort has involved 32 CU-Boulder students, faculty and engineers, including eight undergraduates.