PopSci's 2nd Annual Brilliant 10

XIAOHUI FAN


Cosmology: University of Arizona, Tucson


By detecting faint galaxies, he peers deep within the universe to the start of time.



Xiaohui Fan's astronomy career began in polluted downtown Beijing, where he used his high school's rooftop telescopes to search for comets and flickering variable stars. But he wasn't the romantic stargazer type, communing with infinity. He just wanted to see far. Really far. Some 15 years later and half a globe away, the 31-year-old University of Arizona astronomer now has regular access to the best telescopes in the world. He and his team on the Sloan Digital Sky Survey have already discovered 10 of the oldest objects in the cosmos—one of which, Fan's best catch to date, sent its light our way nearly 13 billion years ago, a scant 800 million years after the big bang.



Back in 1995, while Fan was finishing his master's degree in Beijing, he devised a new approach to searching for very distant quasars—incredibly bright, energetic galaxies with supermassive central black holes. The local facilities weren't powerful enough, so he applied to Princeton University—Sloan headquarters. He essentially said, Here's my plan, I need better equipment, and I'd really like to work with you. Before long, he was collaborating with hundreds of other scientists. "He knew everything about what we were doing before he even got here," recalls Princeton astrophysicist Jeremiah Ostriker.



You can't just pick a point in the sky, point your telescope, and expect to find a 12-plus-billion-year-old galaxy. That's why Fan's goals mesh so perfectly with Sloan, an exhaustive effort to map one-quarter of the visible universe. The 2.5-meter Sloan telescope isn't adept at details, but it covers a huge swath of sky. Fan developed software that sifts through Sloan data, looking for the faint, reddish light that signifies a distant quasar, and whittles millions of objects down to a few hundred candidates.


By comparing Fan's ancient quasars with newer ones, cosmologists hope to learn whether black holes evolve over time. The study of distant quasars may also help resolve a basic chicken-or-egg question: Are black holes a prerequisite or a product of galaxy formation? Fan contributes to theoretical research, but his long-term vision hasn't changed. He wants to keep seeing really, really far. And that almost 13-billion-year-old quasar just isn't good enough. "My goal would be to push it further," he says, "to find the very first ones."



—Gregory Mone