Astronomy, like most scientific fields, is in a state of rapid change. Advances in technology have altered--and continue to alter--the tools and methods of the field, while social changes have brought more women to the discipline; women now make up about 40% of the undergraduate and graduate student members of the American Astronomical Society. Higher up the career ladder, women are much less common, but the numbers are growing steadily.
These changes--both social and technological--are reflected in the careers of two members of astronomy's next generation: UCLA's Andrea Ghez, who studies star formation and the Milky Way's central black hole, and Oak Ridge National Laboratory's William Raphael Hix, who has used his computational expertise to build a reputation for influential collaborations in the study of theoretical nuclear astrophysics.
Andrea Ghez is a pioneer twice over. A professor of physics and astronomy at the University of California, Los Angles (UCLA), she is at the forefront of women in astronomy. Ghez is also at the forefront in another sense: she dives head-first into new experimental techniques. Ghez was among the first to employ a technique called speckle imaging to greatly enhance the resolution of ground-based telescopes, using it to solidify the evidence for the existence of a black hole at the center of the Milky Way galaxy. Later, she applied a declassified military technique to help push the resolution of ground-based telescopes to even greater limits.
Ghez (left) was always interested in black holes. As an undergraduate at MIT in the 1980's, she dabbled in a research project involving the observation of black holes via their x-ray emissions. In graduate school at Cal Tech, she became interested in solving a fundamental problem with ground-based telescopes: image distortion due to atmospheric turbulence. Specifically, she worked with speckle imaging, a time-intensive technique that involves taking many short exposures that can be averaged to produce a higher quality image. She remained frustrated, however, because the signal to noise ratio was still too low to examine black holes in any great detail. So she bided her time, studying the formation of single and binary star systems in stellar nurseries.
In 1992, Ghez went to the University of Arizona as a Hubble fellow to learn about a technique called adaptive optics that had just been declassified from the military. Adaptive optics is another way of correcting for atmospheric distortion; it uses a modified collection mirror with many independently adjustable elements that adjust for distortion in real-time and avoid the computational headaches required by speckle imaging. Although promising, the technique was not yet ready for scientific use at the time.
When she joined UCLA's faculty in 1994, she also joined the adaptive optics group at the Lawrence Livermore National Laboratory, participating in observation runs, writing proposals, and assisting with the development of this innovative technology. Still, it would be years before adaptive optics would benefit her research. Speckle imaging, however, had advanced to the point where it could be used to study the Milky Way's putative central supermassive black hole. Proving the black hole's existence is conceptually simple: If there is enough mass in a small enough volume of space, it must be a black hole. The hard part is in figuring out whether there is or isn't.
Speckle imaging's improved ability to resolve stars near the core of the galaxy provided a measure of the volume, while improved measurements of the characteristics of their orbits around the presumed black hole--also observable courtesy of speckle imaging-- revealed the amount of central mass. The result was a mass about 3 million times that of the sun, and the team narrowed its location to an area comparable in size to our solar system. The object itself is probably about ten times the radius of our sun, but emits no light. "That really tells you it's a black hole," says Ghez.
Her work with the adaptive optics team paid off when the adaptive-optics mirror was installed at UCLA's Keck telescope in 2000. The now-mature adaptive-optics approach was far superior to speckle imaging. In the 2005 viewing season (April through October), the group abandoned speckle imaging altogether and now works solely with adaptive optics. The Keck telescope now boasts the highest resolution of any ground-based or space-based telescope.
Ghez attributes her success to a willingness to tackle ground-breaking, if difficult, techniques. Speckle imaging, she says, "was very intensive, so people tended to stay away from it. But there were a few gold nuggets you could address" with the technique, "such as whether or not there is a supermassive black hole at the center of the galaxy," she says. At different stages of her career, she had to wait for these technologies to become refined enough to be useful. High-risk research with a long-term payout can be risky for a scientific career, but it worked out well for Ghez. "Nothing panned out for years, but [the techniques] did come to fruition. You have to make the investment."
The investment paid off. In 2004, just 10 years after joining UCLA's faculty, Ghez was elected to the National Academy of Science.
Ghez and the field of adaptive optics both continue to push frontiers. The Milky Way's central black hole "is a great laboratory," she says, noting that Einstein's theory of relativity hasn't been tested in a strong gravitational field. "That's the direction we're now going."
The Mad Collaborator
William Raphael Hix (right) is a member of the research staff in the astrophysics theory group at Oak Ridge National Laboratory. He just received Sigma Xi's 2006 Young Investigator award.
Hix's career got off to an inauspicious start. He likes to think of his Harvard Ph.D. project as a "learning experience," one that has served him well. The aim was to find more efficient ways of modeling silicon burning in supernovae in the days leading up to their explosion. In the ultrahigh temperatures of a massive star about to go supernova, silicon nuclei break down into lighter nuclei, which undergo a complex series of reactions to form chromium, manganese, iron, and other heavy elements. "Because of the nature of nuclear processes, you have to solve a matrix. Solving a matrix goes as roughly the cube of the size of the matrix, and silicon burning--with mass numbers around 30, depending on the particular isotope--"has a very large matrix," says Hix.
Hix intended to speed up the calculation. The results were best described as “mixed.” "You use iterative methods" to do the matrix calculation. "I came up with a way that was about ten times faster per iteration, but it required almost ten times as many iterations. It wasn't as useful as we’d hoped," he recalls.
Nevertheless, the work earned him a Ph.D. in 1995 and a license to continue his studies. The project also turned out to provide some useful training, for the experience and the computational tools he developed and mastered. When he joined Craig Wheeler's group at the University of Texas, Hix set about building his niche. Wheeler and collaborators were studying a different type of supernova--one that results from the explosion of a white dwarf--"but the nucleosynthesis processes are much the same." Hix set about applying his knowledge and codes to the new problem.
In 1997, he took a position at the Oak Ridge National Laboratory, which has a small computational astrophysics team that works alongside more traditional nuclear physicists at its particle-accelerator facility. He works closely with the experimental group, feeding new experimental data into his models, yielding predictions that may be observable, such as abundance values for the elements produced in a nova.
The utility of his experience and computational tools, and the widespread role of nuclear astrophysics in astronomical phenomena, allow Hix to stick his fingers in a lot of astronomical pies. For a recent NSF grant application, he had to list advisors, advisees, collaborators and co-authors over the past four years. The list contained 61 names; 53 of them were collaborators or co-authors.
A recent example: Stephan Rosswog, a professor of astrophysics at Germany's International University Bremen, wanted to simulate a white dwarf orbiting a black hole. He found that tidal forces would cause it to compress and heat up enough to initiate nuclear reactions. Hix gave him access to his computational code and taught him how to use it, and later got his name on a paper, which is currently in preparation. "It was a small but important piece of his problem that needed expertise like mine, but it wasn't a problem I’d have investigated on my own," he says.
Because he plays a role in so many wide-ranging projects, a student once described him as "the mad collaborator." He appreciates the compliment, but it's easier for him than it might seem, he says, because he focuses most of his attention on the nucleosynthesis part of any given problem. "My experience has provided me with a specialized tool kit. It's like being a plumber. I can work in every house in the neighborhood. But I concentrate on just the plumbing."
Jim Kling writes from Bellingham , Washington .