Bohdan Paczynski, Pioneering Astrophysicist, Dies at 67

By JEREMY PEARCE
The New York Times
April 26, 2007

Bohdan Paczynski, a leading astrophysicist whose unconventional ideas led to new methods of studying distant stars and hidden planets, including a sweeping nightly survey of the entire sky, died last Thursday at his home in Princeton, N.J. He was 67.

The cause was brain cancer, said a spokesman for Princeton University, where Dr. Paczynski had been a professor of astrophysics since 1982.

In the 1980s, Dr. Paczynski (pronounced pah-CHIN-skee) advanced a technique used by astronomers to detect stars, planets and other bodies that emit faint light or none at all.

The technique, known as gravitational microlensing, works when light from a background star is bent by the gravitational pull of a darker object in the foreground. The result is a magnification of light that yields important information about the fainter object. He explained the idea, based in part on Einstein’s relativity theory, in a paper in The Astrophysical Journal in 1986.

Dr. Paczynski and others subsequently used microlensing to explore the Milky Way and they became the first “to recognize the increasing sophistication of our instruments that made this a practical astronomical tool to probe the galaxy in ways never done before,” said Scott Tremaine, a professor of astrophysics at the Institute for Advanced Study in Princeton.

In 1995, Dr. Paczynski took part in a noteworthy public debate about the mysterious origins of intense bursts of gamma rays, first detected by satellites in the 1960s.

The debate, held in the Smithsonian’s National Museum of Natural History, hinged on whether the rays began within our galaxy or came from more distant sources. Dr. Paczynski theorized that the rays must have emanated from deep space. His antagonist, Donald Q. Lamb, a professor of astronomy and astrophysics at the University of Chicago, argued that the sources were more likely much closer, and said that Dr. Paczynski was “a rather lonely initial advocate for his idea.”

The contest was amicable and inconclusive, ending when Dr. Paczynski’s theory was proved correct in 1997, after scientists were able to study the optical afterglow of a gamma-ray burst. They determined that the burst had “a cosmological source, from galaxies other than our own, and showed how incredibly prescient Bohdan Paczynski had been in his work,” Dr. Lamb said.

With astronomers from Poland, Dr. Paczynski established the All Sky Automated Survey, an attempt to capture a large-scale record of celestial activity and share the results electronically. The project is a continuing effort to find rare events, like cosmic explosions and killer asteroids, which turn on and suddenly turn off and would otherwise not be noticed, Dr. Tremaine said.

Dr. Paczynski had previously helped to start another international collaboration, the Optical Gravitational Lensing Experiment, to detect faint stars and other dark matter from an observatory in Chile.

Dr. Paczynski was born in Wilno, now Vilnius, Lithuania. He received a doctorate in astronomy from Warsaw University in 1964. His early work, on stellar evolution and pairs of stars known as binaries, was conducted at the Nicolaus Copernicus Astronomical Center in Warsaw. He became an American citizen in 1991.

Dr. Paczynski is survived by his wife of 42 years, Hanna; a son, Martin, of Somerville, Mass.; a daughter, Agnieszka, of Washington; and a grandchild.