From star gazer to discoverer

© Thomas Chen

Bohdan Paczynsk, professor of astrophysics, was recently awarded the American Astronomical Society's highest honor.

As a young man growing up in Poland, Bohdan Paczynski gazed upon the stars with fascination. Now, after half a century as an astrophysicist and professor, he fascinates others by discovering planets and stars that cannot even be seen.

Last year, Paczynski supervised an organization that helped to discover the smallest planet ever detected outside of the solar system.

Using a gravitational microlensing technique designed by Paczynski — in which one can detect planets as they magnify the light of their star — astronomers were able to locate a planet about five times the mass of Earth (See related story, pg. 1).

For his groundbreaking research, Paczynski was recently awarded the Henry Norris Russell Lectureship "for a lifetime of eminence in astronomical research" by the American Astronomical Society (AAS). The award is considered one of the most prestigious awards for achievement in astronomy.

The AAS recognized Pacynski "for his highly original contributions to a variety of fields including advanced stellar evolution, the nature of gamma ray bursts, accretion in binary systems, gravitational lensing, and cosmology."

In 1992, Paczynski founded the Optical Gravitational Lensing Experiment (OGLE), an international astronomy project, with colleague and former student Andrzej Udalski, a professor at Warsaw University in Poland.

The two researchers decided to pursue the project to check if the microlensing events, theoretically described by Paczynski, indeed exist.

"This is the field where Paczynski is a real father," Udalski said. "As far as I know, the only hobby of [his] is astrophysics. [Like] many of us, he has a pleasure to join a hobby and work."

"Microlensing events" occur when a planet or star directly aligns with a star behind it and its gravity magnifies the light of that star, making it appear brighter to the observer.

"It was Bohdan Paczynski who in 1991 first proposed using the microlensing events for the search for extrasolar planetary systems," Udalski said.

Paczynski worked at Warsaw University from 1963 until 1981 after receiving his B.A. from there in 1962, studying the evolution of binary stars among a variety of other topics.

"I've changed topics many times during the past half-century," Paczynski said.

Although he periodically visited America to work at places such as the Lick Observatory in California, Paczynski moved to the United States permanently in 1981 to work for the California Institute of Technology. The following year he moved to Princeton and began researching gravitational microlensing and gamma-ray bursts.

"Nobody knew what caused the gamma-ray bursts," said Scott Tremaine GS '75, chair of the astrophysical sciences department. "Paczynski confirmed from the data that these were some of the largest explosions at the edge of the observable universe."

When OGLE began the gravitational microlensing surveys in April of 1992, the original purpose was to study dark matter. When this proved uneventful, the focus shifted to the search for planets in 2000, Paczynski said.

"It is easier to change to another topic than to change technology, because developing technology is more difficult than using it for different research," Paczynski said.

In 1997, Paczynski founded the All Sky Automated Survey (ASAS), based at the Las Campanas Observatory in Chile, which has discovered and continues to monitor over 50,000 stars.

"He took the approach [in these fields] from looking briefly at a random field of the sky to a broader survey of the entire sky with continual observation," Tremaine said.

Throughout his career, Paczynski has continued to collaborate with astronomers from around the world, especially those from his native Poland.

"Salaries are commonly far lower in Poland, so Paczynski has helped lower funding requirements for projects by recruiting many Polish graduate students and astronomers and involving them in his collaborations," Tremaine said.

Paczynski is also a longtime member of the Polish Astronomical Society and International Astronomical Union. Other awards he considers most important in his career are the Henry Draper Medal of the National Academy of Sciences and the Gold Medal of the Royal Astronomical Society in London.