Astrophysicist reaches for the stars – and more

Neta Bahcall extends her excitement about science to students and family

By Steven Schultz

Princeton NJ -- When astrophysicist Neta Bahcall looks at the night sky, she sees not only the stars but also, in her imagination, all the deep space that exists behind them. She sees the detailed structure and ancient remnants of light that reach to the beginning of the universe.

Neta Bahcall

This is not a private moment. It is an experience that she has related many times to students, stoking and nurturing in them the same sense of wonder that has propelled her through her own career. For more than 30 years, Bahcall has helped answer such fundamental questions as the weight, structure and fate of the universe. Insights that once put her at odds with many in her field are now building blocks of modern astronomy.

Bahcall has developed her arguments in scores of journal articles that, according to colleagues, display a solidity of reasoning that is uncommon even among scientists. And she conveys the often-startling picture that emerges with a passion that, according to her students, sets her apart among the best of teachers.

"I always tell them I find it just amazing that we can sit here on Earth, just human beings on this one planet out of billions and billions of stars and planets, and figure out how the universe began and how all this structure was created. I find that just mind-boggling," said Bahcall. "That is what got me excited about astronomy and that is what I tell the students."

Bahcall has served since 1990 as the undergraduate representative for the Department of Astrophysical Sciences, making her the person to whom students go for advice on everything from course selections to graduate school applications. Her enthusiasm for the job has left its mark on a growing number of young researchers.

"She really was, I have to say, the most influential person in my career so far," said Debbie Freedman, who graduated a year ago and is now starting a Ph.D. program in astrophysics at Harvard University. "She is definitely a role model for me."

Bahcall also has led the department in expanding its offerings for students outside the department, particularly for those who are not majoring in scientific fields. She recruited three of the department's most engaging lecturers, Richard Gott, Michael Strauss and Neil Tyson, to team teach a survey course, "The Universe," which draws 250 students and is one of the most popular classes on campus.

Such initiatives have caused the number of students annually enrolled in astrophysics classes to grow from 40 a decade ago to about 350 now. This year, the number will be even higher, nearly 500 students, with the addition of "Theories of the Universe: From Babylon to the Big Bang," a fall semester course taught by visiting professor Joseph Patterson of Columbia University.

Bahcall has a similar mission on a Universitywide level. She directs the Council of Science and Technology, which supports classes, postdoctoral fellowships and visiting professorships aimed at teaching science to non-scientists. Bahcall has greatly expanded the number of course initiatives supported by the council as well as the council's teaching postdoctoral fellowship program.

For the handful of students each year who major in astrophysics, Bahcall is a mentor and advocate. Freedman recalled how Bahcall stopped her in the halls to put scholarship applications into her hand, helped her find summer research opportunities three years in a row and counseled her in an agonizing decision about graduate school. "She helped me build my career from early on and one opportunity led to another," Freedman said.

Julie Comerford, now a first-year graduate student at the University of California-Berkeley, met Bahcall during her sophomore year when she was shopping for a major and visited the astrophysics department's open house. "Neta was the first person I saw down there and she had this big, huge friendly smile. It just set the tone for everything I encountered in the department," said Comerford.

Bold and exciting

Bahcall's own scientific interests began as a high school student in Israel when she found herself attracted to math and physics courses. "I was just fascinated to understand how the world works," she said. She continued studying math and physics at Hebrew University, but was not exposed to astronomy until she moved to the California Institute of Technology, where her husband, physicist John Bahcall, was a young faculty member. By the time she received her Ph.D. from Tel Aviv University in 1970, she had already begun collaborating with Caltech scientists on problems of nuclear reactions in stars and of the nature of quasars.

Bahcall joined the professional research staff at Princeton in 1971 when her husband was appointed to the permanent faculty of the Institute for Advanced Study. She stayed at Princeton until 1983, when she moved to the Space Telescope Science Institute as leader of the group that developed and administered the science program of the Hubble Space Telescope. In 1989, she returned to Princeton as a professor of astrophysics.

Her research has made her a world leader in finding innovative, yet straightforward ways to interpret the flood of astronomical data that has been coming from many sources, including the Hubble, the Sloan Digital Sky Survey and various efforts to chart the cosmic structure of the universe.

Among her many contributions has been determining what astronomers call the mass density of the universe -- essentially, how much matter the cosmos contains -- which is critical for understanding the evolution of the universe and predicting its fate. Bahcall and Princeton colleague Renyue Cen pioneered a statistical method for analyzing the distribution of giant clusters of galaxies and concluded that the universe contains far less material than many scientists had previously supposed.

The initially unpopular idea meant that the universe was relatively lightweight and could never muster enough gravity to counteract the expansion caused by the big bang. It meant that the universe would expand forever, a conclusion that is now widely accepted.

"To go against accepted wisdom is both bold and exciting, and she has done that," said Princeton physicist James Peebles. At the same time, he said, the one word he would use to characterize her work is "solid." "When she says something, it is because she has thought it through," Peebles said. "At a conference, if somebody says something that is incautious it may well be Neta who will politely, but very firmly, explain why that 'ain't necessarily so.'"

Bahcall's achievements have been widely recognized. She was elected in 1997 to the U.S. National Academy of Sciences. She has served as vice president of the American Astronomical Society and was recently nominated as a candidate for president of the society.

An open door

Students who work with Bahcall on junior papers and senior theses experience her scientific rigor firsthand. A year after the open house that brought her to the department, Comerford worked with Bahcall on a junior paper. She launched into one of Bahcall's most recent innovations, which is to measure the ratio of visible light to detectable matter in galaxies as a way of further refining the mass density of the universe.

Even though Bahcall broke the daunting project into manageable pieces, Comerford was shocked when the semester ended and Bahcall said it was time to prepare the work for publication. The paper, with just Bahcall and Comerford as authors, appeared in the Jan. 20, 2002, issue of the Astrophysical Journal, a premier journal in the field.

"At first I didn't even know how to look up a citation," said Comerford. "She just took me through it. It was all new to me. By the end, we had contributed our own article to the searchable database. It just amazes me."

That experience set the bar for all her future research, including her senior thesis, which she also published, said Comerford. "If it hadn't been for her pushing me every step of the way, I wouldn't be here."

Comerford recalled going to Peyton Hall with a question one evening just before Bahcall was about to leave for an important conference. "Even then her door was not all the way closed, it was still open a crack so you knew that you could go in if you needed to," Comerford said.

A family in science

Next to that open door is another tribute to Bahcall's ability to nurture scientists, in a more literal sense. A poster titled "Families in Science" hangs on the wall and shows pictures of the Bahcalls and their three children. The oldest, Safi, has a Ph.D. in physics from Stanford and is now chief executive of a biotechnology company; Dan has a Ph.D. in cognitive psychology from Rutgers University; and Orli, a Marshall fellow from the Massachusetts Institute of Technology, is getting a Ph.D. in epidemiology from Imperial College of London.

Bahcall said she and her husband never pushed their children to become scientists, but certainly exposed them to the excitement of their field. And, in the end, that is all she wants for her students. She recalled one student who, after taking "The Universe," told her how much more detail he now sees in the night sky and how he would never look at it in the same way again. "That is what I want them to think about," said Bahcall. "It's not that I want them to be professors of astrophysics, but just know a little bit more about our magnificent universe. My goal is that every student who graduates from Princeton will learn something about what our universe is all about."

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