PITT ASTRONOMER MAKES STELLAR DISCOVERY USING THE HUBBLE SPACE TELESCOPE

PITTSBURGH, Jan. 27 -- Blue dwarf galaxies are the most numerous observable formations in the universe and because of their color and other characteristics have long been thought to be young galaxies, still in the process of formation today.

Now, using the Hubble Space Telescope, University of Pittsburgh astronomer Regina Schulte-Ladbeck has discovered that blue dwarf galaxies may not be young at all. News of Schulte-Ladbeck's research was published in the Jan. 20 edition of Nature and the research itself appeared in the Jan. 22 issue of Astrophysical Journal Letters.

"My main area of interest has been in young, new stars, so it was natural that I would look at a dwarf galaxy. From the ground they look blue, and blue stars are generally younger than yellow or red stars," said Schulte-Ladbeck. "The real question is one of how galaxies are formed, and the hypothesis was that dwarf galaxies would show us that galaxy formation is an ongoing process, that new galaxies might be forming even today."

"We used the wide-field planetary camera on the Hubble Telescope to look at a very small patch of sky, roughly the same size as focusing on a dime from three miles away," said Schulte-Ladbeck.

What that Hubble images showed was quite unexpected. "There were many blue stars, as expected," said Schulte-Ladbeck. "But we noticed a large number of stars in the outer edges of the galaxy that registered in the infrared, meaning they weren't young stars, but quite the opposite. These blue compact dwarf galaxies were the best candidates we've had for the case that galaxy formation is still happening now. But the presence of clearly older stars seems to rule that out. This evidence shows that galaxy formation is unlikely to be an ongoing process."

This discovery has Schulte-Ladbeck and her colleagues, Mary Crone of Skidmore College and Ulrich Hopp of the Munich Observatory, on the Hubble Space Telescope schedule again this year. They will use the Hubble Near Infrared Camera and Multi-Object Spectrometer (NICMOS) to look at more blue compact dwarfs, this time looking specifically for red stars.

"NICMOS is the newest camera on the Hubble telescope, installed in

1997," said Schulte-Ladbeck. "Using it allows us to look at galaxies that are much farther away. So now we'll look at five other dwarf galaxies to see if we can find old stars in these 'young' galaxies to confirm what we've found so far."