Hopkins' orbiting observatory starts to send data on Milky Way galaxy

Early technical glitches fixed

astronomers study life cycle in outer space

January 13, 2000|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

After a bumpy start, a Johns Hopkins-based orbiting observatory has begun to send back important new findings on the life cycles of stars and galaxies.

Scientists working with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite told astronomers meeting in Atlanta yesterday they have found clouds of hot gas surrounding our Milky Way galaxy, blown there by the explosions of dying stars.

FUSE has also given astronomers their first look at the vast, wispy clouds of cold molecular hydrogen -- the raw material for new stars -- long-supposed to float throughout the Milky Way.

"The FUSE observatory is now open for routine business," said Hopkins physics professor H. Warren Moos, principal FUSE investigator. He is presiding this week over the presentation of 25 papers by FUSE scientists to the American Astronomical Society.

To Moos and his team, the papers are vindication for FUSE after an orbital check-out period bedeviled by technical problems. Most of them have now been resolved, or managed, Moos said.

"We're still tuning the satellite to get the best resolution and the highest sensitivity," he said. But FUSE is breaking new ground now. "This is good stuff," he said.

The $108 million FUSE observatory was designed and built at Hopkins, and is operated 24 hours a day from a control center on the Homewood campus in Baltimore.

FUSE was built to give astronomers a view of the universe in a largely untapped part of the ultraviolet portion of the electromagnetic spectrum.

It does not take pictures, but breaks down ultraviolet light to reveal the chemistry and physics of the stars and galaxies, or the dust and gas through which their light has passed.

FUSE was launched in June to an orbit 477 miles high. But a series of problems delayed routine science operations by two months.

The mission's ground station in Puerto Rico broke down repeatedly, and radiation unexpectedly knocked out data in the spacecraft's computer when FUSE flew over the South Atlantic region where Earth's radiation belts dip low into its orbital path.

The FUSE team also found tiny but important misalignments of the spacecraft's four mirrors caused by solar heating of the telescope.

Engineers have fixed, or learned to work around, the problems, and "we're getting better at it," Moos said.

FUSE's unique view of space and unprecedented sensitivity have given astronomers their first look at the most abundant molecules in the universe -- molecular hydrogen, composed of two single hydrogen atoms. The molecules coalesce into dense, cold clouds that "are the star nurseries from which new stars and planets form," said University of Colorado astronomer Michael Shull.

Shull's team has detected wispy clouds of molecular hydrogen floating close to the plane of the Milky Way, Moos said. FUSE has found the hydrogen clouds in the same places where other astronomers found clouds of interstellar dust forged in stars and blasted into space by stellar explosions.

Moos said the dust grains may in fact provide a platform where hydrogen atoms can meet to form molecular hydrogen.

FUSE has also confirmed the presence of a halo of extremely hot gas surrounding the Milky Way. Astronomer Lyman Spitzer predicted the halo's existence 45 years ago, saying it would be composed of such "heavy" elements as carbon, silicon, iron and oxygen, forged deep inside stars from lighter elements.

When those stars exhaust their nuclear fuel and explode into supernovas, the heavy elements are shot into interstellar space, where they become the building blocks of new stars, solid planets and all living things.

Spitzer proposed that some of the star-forged material would emerge above and below the galactic plane, like half-million-degree steam rising off a plate of pasta. And that's exactly where astronomer Blair D. Savage of the University of Wisconsin-Madison found it.

The study of stellar recycling is central to FUSE's mission, said George Sonneborn, a project scientist for NASA.

"The life cycle of stars and elements in the galaxy is of interest to us because it's the stuff we're made of," he said.

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