Dwarf galaxies provide clues on star formation

Peter Kauffner

Although they have been ignored until recently by cosmologists, dwarf galaxies might answer some of scientists’ questions about star formation and the development of the universe, said Evan Skillman, an associate professor of astronomy, at a colloquium held Friday at the University.
“Dwarf galaxies are a growth industry,” he said.
A dwarf galaxy is a galaxy with less than 5 percent of the stars found in an average galaxy, such as the Milky Way, where our solar system is located. The Milky Way is estimated to contain about 100 billion stars.
“If you go to Cambridge (University), they are interested only in galaxies with high red shifts,” Skillman said. A high red shift indicates that a galaxy is very far away, perhaps as far away as 10 billion light-years.
Because galaxies with high red shifts are so distant, the light Earth receives from them was actually emitted billions of years ago. Therefore, such galaxies are thought to contain clues as to what our galaxy was like long ago.
But Skillman argues that nearby galaxies should not be overlooked. “You can do cosmology in your own backyard,” he said.
Telescopes can provide astronomers with more complete data about nearby galaxies than they can about distant ones. Scientists can gather particularly good data about galaxies in the Local Group, a cluster of galaxies that are all located within two million light years of the Earth.
Galaxies start off as a mass of hydrogen that gradually condenses to form stars. When many stars form around the same time, astronomers describe the event as a “burst” of star formation.
The pattern of star formation in smaller galaxies tends to be less complex than in larger galaxies, a fact that has given rise to much of the attention dwarf galaxies are now receiving.
“In a large galaxy you have many cells of star formation, so they get blended together. But if you have a little galaxy, a burst will have an identity because it won’t be masked by a burst in another place,” Skillman said.
Skillman and his fellow researchers collect data from the Hubble Space Telescope and other sources to chart characteristics such as the color, brightness and metal content for the many stars in various dwarf galaxies. This creates a “fossil record” that allows researchers to determine the rate of star formation at various times in a galaxy’s history.
Skillman’s research is funded by a grant from the National Aeronautics and Space Administration.
“If we could understand how many stars were being born per time interval over the history of universe, that would be the Holy Grail right there,” he said.