UW News

October 5, 2006

UW ‘stellar archaeologist’ gets biggest share of Hubble observing time

News and Information

It’s not unusual for UW astronomers to use the Hubble Space Telescope in their research, but for the first time a UW scientist has been granted the largest share of observation time for an entire year.

Julianne Dalcanton, an associate professor of astronomy, is working on a detailed analysis of the origin and composition of stars in galaxies 6 million to 12 million light years from our own galaxy, the Milky Way. (A light year is about 5.88 trillion miles.) To gather the data needed for the ambitious project, she was granted 295 Earth orbits, or nearly 450 hours of observation time, for the year that started in July.

The telescope has the ability to peer farther into space with greater detail than earthbound telescopes, so it can provide a wealth of information about stars inhabiting galaxies in our celestial neighborhood.

Each star, by its color and brightness, gives clues about when it formed, what it is made of and what fuel it is burning. Stars that are stable are using the hydrogen in their cores as fuel, converting it to helium. When the hydrogen runs out, the stars begin to collapse and start burning helium, converting it to carbon. The various stages of a star’s life cycle, along with its age and other characteristics, can be detected from the observed brightness and color. Some of the red stars detected in Dalcanton’s observations are more than 10 billion years old, while some of the bluest stars are as young as a few million years old.

“By analyzing the properties of the stars, we can begin untangling the history of the galaxies. It’s stellar archaeology,” Dalcanton said. “The stars are all fossils left behind from galaxy formation. You can look at each galaxy and discover what it was doing, where it was doing it and when it was doing it.”

Dalcanton began the project after examining an earlier Hubble image of a tiny part of a nearby galaxy. When the image was analyzed, she and her collaborators discovered that one small frame carried a wealth of highly detailed information about individual stars and the galaxies in which they reside. She realized Hubble could capture comprehensive information for a number of nearby galaxies and felt it would be a major loss to the scientific community if that was not accomplished before 2010, when Hubble is scheduled to end its service.

Dalcanton submitted specific observing plans to the Space Telescope Science Institute, which operates Hubble on behalf of the National Aeronautics and Space Administration. Her observations, made with the Advanced Camera for Surveys, are being interspersed with those of other scientists throughout the year. The collected data will be sent digitally to her and 15 to 20 other scientists who are part of an international research collaboration. They will correlate all of the data to create a complex view of nearby galaxies.

“Every visualization is done on the computer,” she said. “What comes down from the telescope are ones and zeros, then we turn it into something that people can interpret.”

The project will return new information on about 60 galaxies and analyze existing data for another dozen galaxies, said Ben Williams, a UW astronomy research associate who is working on the project.

Williams received his doctorate from the UW in 2002 and was working at Pennsylvania State University when he learned of Dalcanton’s project. The work closely matches his research interests, so he returned to the UW in July, just as the first data was about to arrive.

“We’ve already got more Hubble data than I’ve ever worked with myself, and this is only the start,” he said. “We’re going to be busy for a long time.”