The moment the Far Ultraviolet Spectroscopic Explorer team has been waiting for finally came last week.
FUSE, they told the American Astronomical Society, is open for business. And since the proof of any new business is in its product, they presented 25 scientific posters filled with tantalizing new data gathered in the orbiting observatory's first few months of activity.
One highlight, described at a press conference in Atlanta, was new evidence on the origins of a cloud of hot gas that surrounds the Milky Way galaxy, stretching out 5,000-10,000 light-years in a football-shaped halo.
"The hot gas halo has been known for some time, but we weren't sure how it got there or stayed hot," said FUSE co-investigator Blair Savage of the University of Wisconsin in Madison. "The new FUSE observations reveal an extensive amount of oxygen VI (oxygen atoms that have had five of their eight surrounding electrons stripped away) in the halo. Some scientists thought that ultraviolet radiation from hot stars could produce the halo, but the only way to make the observed amount of oxygen VI is through collision with the blast waves from exploding stars, called supernovae."
The finding supports the "galactic fountain" theory, which suggests that supernovae blow hot gas outward in all directions, but because there's less material above and below the plane of the galaxy, the gas can expand farther in these directions and create a bubble above or below the galaxy.
Hopkins astronomer Edward Murphy used FUSE to gather data on what's believed to be the next stage of the process: high-speed clouds of gas falling into the galaxy, which were first detected 40 years ago by Dutch astronomers. In the "galactic fountain" model, the clouds are formed when gas in the halo cools and falls back into the galaxy. The gas falling back into the galaxy eventually forms new stars, starting the cycle over again.
"It may be a bit like the water cycle on Earth," Murphy says.
Murphy has used FUSE to get more detail than previously possible on one complex of high-velocity clouds, and plans to analyze several, paying close attention to their metal content. The metals in the clouds can link them to supernovae, revealing how many times the cloud's contents have been processed by stars. Scientists believe the nuclear furnaces of stars fuse simpler elements present from the beginning of the universe into heavier, more complex elements like metals.
So far, the data from FUSE and other sources suggest the link to supernovae may be correct. "Most of the clouds we've looked at so far have metals that have been processed by stars at least once, and perhaps twice," Murphy says. But Murphy notes that it's too early to say that for all high-velocity clouds, and he holds out hope that one of the clouds might be a "primordial cloud," untouched by stellar processing.
"If we could find a cloud like that, it would help us further establish the relationship between loss of deuterium, a form of hydrogen created only in the Big Bang, and the creation of metals," Murphy says. "That would help us extrapolate back to conditions at the time of the Big Bang."
Other Hopkins presenters included astronomer Jeff Kruk, describing initial results of a look at a star caught on the cusp of old age; and FUSE mission planning chief Bill Blair and postdoctoral researcher Ravi Sankrit, detailing their observations of the remnant of a supernova.
Findings presented by FUSE scientists from other research institutions included new information on the incredible wind that blows off some very bright, hot stars, and how this wind differs in our galaxy and a nearby galaxy known as the Large Magellanic Cloud; and a survey of the presence of cold clouds of molecular hydrogen that are believed to be the birthing grounds of new stars and planets.
All of this new data, it might be noted, has been produced in just the first few months of observation, and there's much more to come. In the spring, as they continue to optimize FUSE's abilities, researchers expect to be able to begin a comprehensive study of the abundance of deuterium.