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Probing the Evolution of Galaxies

Ann Wehrle
Ann Wehrle '78

Ann Wehrle '78 is eagerly awaiting the arrival of spring, when NASA's launch of the Gamma-ray Large Area Space Telescope (GLAST) will enable her to observe a phenomenon that will shed light on the evolution of galaxies. A senior research scientist with the Space Science Institute, Boulder, Colo., Wehrle studies the most powerful objects in the universe—black holes and the quasars they drive—which are at the center of many galaxies.

"The magnetic fields and winds around black holes are the most powerful accelerators in the universe, and that's why they are interesting," Wehrle explains. "In a quasar, there is a central black hole with an accretion disk where matter accumulates. Most of this matter eventually falls into the black hole. Then, for some reason we do not understand, some of it is channeled outward along the rotational poles of the black hole, shooting out at relativistic speeds—virtually the speed of light."

Imagine relativistic jets as if they were composed of a line of peas. "Each pea represents a unit of relativistic plasma—when astronomers are feeling stuffy, we call it a component; otherwise, we call it a blob. These produce radio emission and gamma-ray emission," Wehrle says. "A burst of gamma ray emission signals the moment when a blob coalesces in the relativistic jet and starts to move outward."

Wehrle says the energy of the relativistic jets works its way through the galaxy, eventually "dumping" into intergalactic space, thereby applying pressure to this medium. In this way, she says, "The central black hole affects the evolution of its parent galaxy and galaxies in its neighborhood." In turn, a "feedback mechanism" alters the jets themselves.

By providing gamma-ray data, which can only be gathered in space, GLAST fills in a blank in the electromagnetic spectrum of data that are available from ground-based telescopes operating in the ultraviolet, optical, infrared, millimeter, submillimeter, and centimeter wave bands. "The combined behavior at various wavelengths tells us about the processes going on in the relativistic jets," Wehrle says.

Because of her experience with a previous spacecraft, the Compton Gamma Ray Observatory, Wehrle also served on the GLAST user committee representing a group of 100 to 200 scientists who will use the spacecraft to study various astronomical objects.

Planet Quest

After graduating from Bryn Mawr, Wehrle worked at the Jet Propulsion Laboratory (JPL) at the California Institute of Technology (Caltech) in Pasadena, using quasars as reference beacons—think of them as lighthouses—for spacecraft navigation. Following completion of her doctoral degree at the University of California, Los Angeles, she returned to Caltech as a member of a team studying quasars using long baseline interferometry, which assembles data recorded by multiple radio telescopes in the United States, Europe, Australia, and South Africa.

"Interferometry requires at least two functional antennas working at the same frequency and polarization," Wehrle says. "We must cooperate to obtain the data." In fact, Wehrle says, "Astronomers are no longer working alone in the dark with their telescopes."

In 2000, NASA appointed Wehrle to the Science Team of the Space Interferometry Mission, since renamed SIM PlanetQuest, as a principal investigator (the only woman) for one of the mission's 10 key science projects. It is anticipated that her study will provide new and unique insights into the physical processes in quasars and active galaxies. She and her co-investigators have been allotted three percent of the observation time—a significant fraction—on the space observatory. "It uses a different technique, which will allow us to look much deeper into the relativistic jets than we can through any other method," she says. The launch date has not been set.

In July 2007, Wehrle used several NASA spacecraft to study relativistic phenomena near black holes. One of her classmates, Marilyn Newhouse '78, worked on NASA's Hubble and Chandra observatories, and Jean H. Swank '63 is project scientist for NASA's Rossi X-ray Timing Explorer.

Women in Science

Born in 1956, Wehrle says she took advantage of the nation's strong initiatives in math and science education after the launch of Sputnik. However, she recalls, "There were few girls going into math and science. The first astronomer I ever met, at age 17, was Alma Zook, and she was influential for me." Wehrle still collaborates with Zook, who is a professor of physics and astronomy at Pomona College.

"As I grew older, I realized that it helps girls to see women in the sciences," Wehrle says. "So I have tried to reach out to girls and younger women who are making careers as scientists."

According to a 2005 study by the American Institute of Physics, the number of women in astronomy at all levels is increasing. Yet in 2003, women earned 46 percent of bachelor's degrees and only 26 percent of doctoral degrees in the field. "I think the hardest part of being a woman in the field is often being the only woman on a committee or a project," Wehrle observes. "You have to talk louder, and you have to make your point several times."

Apropos of her profession, Wehrle, her husband, and their two children live on a street named Stardust Road, which is just a short stroll from Galaxy Heights.

Dorothy Wright contributes news and feature articles on science, technology, engineering, and general-interest topics to a variety of publications, including Civil Engineering and Engineering News Record.