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4:00 PM 10/6/1999

Hubble space telescope reveals inner working of galaxy bulges
By RANDOLPH E. SCHMID, Associated Press Writer
WASHINGTON (AP) -- The millions of stars bulging out amid the massive spiral galaxies whirling through space are beginning to reveal some details of how these star groups formed, NASA reported Wednesday.
The central bulges of the more tightly wound spiral galaxies formed early in the life of the universe, according to a team led by Reynier Peletier of the University of Nottingham in England.
A second team, led by C. Marcella Carollo of Columbia University in New York, concluded that galaxies with small bulges and long bars or lines of stars that bisect the nucleus grew more recently and through different processes.
The researchers say the central bulge stabilizes a galaxy's development and largely controls the ebb and flow of star birth in the core.
The Hubble telescope allows astronomers, who had previously been able to study only the bulge at the center of our own galaxy, to peer deep inside the bulges of other galaxies.
Carollo's team said the central bulge in the galaxies they studied probably formed early in the history of the universe, but was later fed by gas flowing into the galaxy's core, caused by instability in the surrounding disk of stars.
The gas fueled the birth of new stars, and the bulge grew, with bright star clusters populating the center. They found both young and old stars in the bulge.
Peletier's researchers studied the center of 20 spiral galaxies that have large bulges. They concluded that elliptical bulges of stars formed over a relatively brief period very early in the young universe, either through the collapse of a single cloud of hydrogen or the merger of primeval star clusters.
"The bulges of early spiral galaxies are old, and at least the outer parts of their disks are considerably younger," Peletier said in a statement.
The groups used Hubble telescope to study more than 200 neighboring galaxies, out to a distance of 100 million light years. A light year is the distance light travels in a year.
Using visible light and infrared cameras, they were able to determine the stars' true colors. Older stars tend to be redder, but space dust can interfere with color perception from Earth. The Hubble space telescope permitted the researchers to look past that dust.
Peletier's report is scheduled for publication in Monthly Notices of the Royal Astronomical Society and Carollo's work will appear in Astrophysical Journal.