Bohdan Paczynski, renowned astrophysicist, dies at age 67 (Forwarded)

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For immediate release: April 24, 2007

Bohdan Paczynski, renowned astrophysicist, dies at age 67

Princeton astrophysicist Bohdan Paczynski, whose insights into the nature of
celestial phenomena guided many developments in his field, died April 19
after a three-year battle with brain cancer. He was 67.

Paczynski's pioneering efforts to develop the technique called gravitational
lensing permitted the discovery of the first terrestrial planet found
outside our solar system. Despite widespread skepticism from the
astrophysics community, he also championed the idea that the
still-mysterious events known as gamma ray bursts originated billions of
light years away rather than within our own Milky Way galaxy -- a theory
that was ultimately confirmed by observations.

"He was incredibly creative and original," said Michael Strauss, a professor
of astrophysical sciences and a colleague of Paczynski's. "All his life he
brought interesting approaches to interesting problems."

Paczynski was also well respected for both his enthusiasm for teaching and
his support for other astronomers, on campus and around the world. One of
the world's foremost experts on the lives of stars, he routinely opened the
minds of the undergraduates who took his courses on stellar evolution and
mentored many graduate-level scientists as well.

"Bohdan was always the center of our daily departmental gatherings," said
David Spergel, chair of the astrophysical sciences department. "He brought
perspective to our conversations about stars and everything else as well. He
didn't just teach students. He taught us too."

Paczynski obtained his Ph.D. in astronomy from Warsaw University in his
native Poland and spent 20 years at what is now Warsaw's Copernicus
Astronomical Center, where he attained the rank of professor in 1979. He
came to Princeton in 1982 and in 1989 was named the Lyman Spitzer Jr.
Professor of Theoretical Astrophysics.

His early career was defined largely by his studies of the interesting ways
stars can change, beginning with his teenage observations of double stars
called binaries, whose combined brightness can vary dramatically when one
eclipses the other.

Because gravity bends light rays, a star passing directly in front of
another can focus the background star's light in a manner akin to a
telescope lens. Paczynski showed that this effect could be applied to survey
the population of stars in our galaxy. Now known as gravitational
microlensing, the technique has enabled astronomers to determine the mass of
the stars in the Milky Way.

"Einstein's theory of relativity predicts that gravitational lensing should
occur, but Bohdan first worked out its technical underpinnings," said
astrophysicist Jeremiah Ostriker, who first brought Paczynski to Princeton.
"He turned it into a backyard science that has produced our best catalog of
the most stars."

A consortium of astronomers led by Paczynski eventually founded the Optical
Gravitational Lensing Experiment (OGLE), which has witnessed thousands of
lensing events and now has a telescope at Chile's Las Campanas Observatory
dedicated to searching for more. Paczynski's efforts revealed that stars,
even including small, faint ones, could not fully account for the gravity
holding our galaxy together, demonstrating the presence of the substance
known as dark matter.

"The next thing Bohdan realized was that when you observe lensing that
often, you can do other clever things, such as use it to look for planets
around faraway stars," Strauss said. "If there's a planet orbiting the
foreground star, the planet will subtly change the lensing signature, which
can be used to infer the existence of the planet."

These insights led to OGLE's discovery last year of one of the smallest
planets known to exist outside the solar system: a rocky planet five and a
half times the size of Earth orbiting a star more than 20,000 light years
away. Some 70 astronomers were on the team that made the discovery, but
Spergel said Paczynski was the acknowledged intellectual leader.

"His influence on the field was enormous," Spergel said. "Entire subfields
of astrophysics either would not have existed without him, or would have
been radically different."

Paczynski's colleagues mentioned his perceptions about gamma ray bursts as a
prime example.

"People have known about these mysterious bursts of energy since the Cold
War, and everyone thought that with such high luminosity they must originate
somewhere within our galaxy," Strauss said. "Bohdan looked at the data and
said, maybe it's not so crazy to think they are from much farther away.
Other astrophysicists thought he was nuts, but he turned out to be right."

Paczynski, whose generosity toward others was legendary, maintained strong
relations with the astronomy community in Poland, and he hosted a steady
stream of visitors from his homeland.

"The role of Professor Paczynski in the development of modern Polish
astronomy is enormous," said Andrzej Udalski, a professor of astronomy at
Warsaw University. "He was always full of bright ideas and shared them with
his many collaborators. To many of them, the collaboration with Paczynski
was a crucial point in their careers. Practically every active Polish
astronomer in the last 40 years was in one or another way influenced by
him."

Many of his research partners on the OGLE experiment are from Poland, and
Ostriker said Paczynski was instrumental in bringing several promising
Polish scientists to visit American universities.

"He was always trying to give credit and support to others," Ostriker said.
"He was an extremely modest man. Bohdan would tell me, 'I have no expertise
in anything -- I just do things based on common sense.' But he had an awful
lot of common sense."

Paczynski received many honors, including the Gold Medal of the Royal
Astronomical Society and the 2006 Henry Norris Russell Lectureship, the
highest award of the American Astronomical Society. He was a member of the
Polish Academy of Sciences and the U.S. National Academy of Sciences.

He is survived by his wife, Hanka, and their two children, Agnieszka and
Martin.

A University memorial service will be scheduled at a later date. Memorial
contributions may be made to the Brain Tumor Society Ride for Research in
which Martin is participating.