A FUSE (Far-Ultraviolet Spectroscopic Explorer) tipsheet
for the 2000 American Astronomical Society meeting
In addition to the findings highlighted by NASA at its FUSE press conference, researchers from the Johns Hopkins University will present data from FUSE on the following topics at the American Astronomical Society meeting.
Background material on FUSE follows the tips.
High-velocity clouds may hold clues to galaxy's development and the Big Bang
Forty years ago, Dutch astronomers were the first to observe a galactic oddity: clouds of gas falling into the plane of the galaxy at inexplicably high velocities up to a few hundreds of kilometers per second.
One theory on the origin of these clouds, backed up by new FUSE information featured in the NASA press conference, suggests that gas may have been blown up out of the plane of the galaxy in a colossal bubble created by the explosive self-destruction of clusters of large stars.
"It may be a bit like the water cycle on Earth," says Edward Murphy, a research scientist at Hopkins. "Hot gas is blown out of the galactic plane by supernovas, eventually cools, and then falls back into the galaxy to form new stars." According to the theory, the high velocity clouds form when the gas falls back.
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 supernovas, 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 supernovas 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," says Murphy. But Murphy notes that it's too early to say that for all high-velocity clouds, and 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," says Murphy. "That would help us extrapolate back to conditions at the time of the Big Bang."
Star entering old age provides important glimpse of stellar innards
Hopkins astronomer Jeff Kruk (pictured at left) turned FUSE's powerful gaze onto a rare and potentially valuable target: a star caught on the cusp of old age. The resulting data should provide a uniquely detailed peek at the makeup of the middle layers of a star, where researchers believe some of the heavier elements important to planetary formation are created.
From a medium or small star's perspective, the transition to old age occurs practically overnight perhaps as quickly as 10,000 years in a lifespan measured in millions or billions of years.
For a brief time as the star's core fuel runs out and it blows off the remaining material in its outer layers, the star's middle layers stand exposed as never before. But by the time the star reaches the final stages of its life, the composition of these layers has been altered by its contraction into a white dwarf.
Kruk's FUSE observations focused on K1-16, a planetary nebula in the halo of our galaxy. Created when a star begins the transformation into a white dwarf, a planetary nebulae is a cloud of gas blown off by the star and brightly lit by it.
"K1-16 appears to still be hot enough that the data we get from FUSE should allow us to see some traces of heavier elements on its surface and assemble a model of the composition of its atmosphere," says Kruk.
Supernova's shockwave creates unusual forms of elements
Scattered around space are the remnants of stars whose larger mass forced a more cataclysmic entry into old age, the violent explosion known as a supernova.
FUSE chief mission planning scientist Bill Blair (pictured at right) and postdoctoral researcher Ravi Sankrit used FUSE to study a supernova remnant in the Large Magellanic Cloud, a smaller galaxy that neighbors our home galaxy, the Milky Way.
"This remnant is a nice target for observation by FUSE because we can look for the spectroscopic signatures of different elements both in the light the remnant emits and in the gas from the Magellanic Cloud that this light passes through on its way to Earth," says Sankrit.
"As the shockwave from the supernova passes through the surrounding space, elements in the shockwave and surrounding space are stripped of many of their electrons, changing them into ions that are easier to recognize spectroscopically."
"Both what's in the star and what's in the space around it are important to our understanding of the chemical processes that take place in stars, Sankrit explains, noting that both the elements they see in the spectrum from FUSE and the elements they don't see can give them a better feel for the environment around the star."
To expand astronomers' understanding of the birth and death of stars, and the creation of new, heavier elements from primordial deuterium, Blair and Sankrit plan to use FUSE to study several more supernova remnants.
Background on FUSE
Perched above the obscuring effects of Earth's atmosphere and specially designed to focus hard-to-handle wavelengths of light, FUSE provides astronomers with a nearly unprecedented view of the universe. The observatory has finished its checkout phase and is now accepting proposals for observation projects.
FUSE doesn't take pictures; instead, it lets researchers analyze high-frequency ultraviolet wavelengths of light. When this light is broken down into its component wavelengths, irregularities in the light reveal information about the elemental makeup of the objects that create the light stars and galaxies--and about material the light has passed through on its long journey to Earth a hard-to-observe mixture of gases and dust.
To keep costs down and keep the FUSE project viable, Hopkins scientists offered in 1995 to manage the project from their campus. In a first for a project of this magnitude, NASA accepted. A team of scientists, engineers, contractors, and students manage FUSE from a control room on the first floor of the Bloomberg Center for Physics and Astronomy, and FUSE's costs are currently at less than 50 percent of the original estimated budget.
Collaborators with Hopkins and NASA in the FUSE project include the University of Colorado at Boulder, University of California at Berkeley, the Canadian Space Agency, the French Space Agency, and corporate partners.
FUSE is among the first projects in NASA s Origins Program under its Office of Space Sciences.
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