Press Release

Cosmic Magnifying Glass: Distant Star Reveals Planet

By SpaceRef Editor
April 15, 2004
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Cosmic Magnifying Glass: Distant Star Reveals Planet

Like Sherlock Holmes holding a magnifying glass to
unveil hidden clues, modern day astronomers used cosmic
magnifying effects to reveal a planet orbiting a distant

This marks the first discovery of a planet around a star
beyond Earth’s solar system using gravitational
microlensing. A star or planet can act as a cosmic lens to
magnify and brighten a more distant star lined up behind it.
The gravitational field of the foreground star bends and
focuses light, like a glass lens bending and focusing
starlight in a telescope. Albert Einstein predicted this
effect in his theory of general relativity and confirmed it
with our sun.

“The real strength of microlensing is its ability to detect
low-mass planets,” said Dr. Ian Bond of the Institute for
Astronomy in Edinburgh, Scotland, lead author of a paper
appearing in the May 10 Astrophysical Journal Letters. The
discovery was made possible through cooperation between two
international research teams: Microlensing Observations in
Astrophysics (MOA) and Optical Gravitational Lensing
Experiment (OGLE). Well-equipped amateur astronomers might
use this technique to follow up future discoveries and help
confirm planets around other stars.

The newly discovered star-planet system is 17,000 light
years away in the constellation Sagittarius. The planet,
orbiting a red dwarf parent star, is most likely one-and-a-
half times bigger than Jupiter. The planet and star are
three times farther apart than Earth and the sun. Together,
they magnify a farther, background star some 24,000 light
years away, near the Milky Way center.

In most prior microlensing observations, scientists saw a
typical brightening pattern, or light curve, indicating a
star’s gravitational pull was affecting light from an object
behind it. The latest observations revealed extra spikes of
brightness, indicating the existence of two massive objects.
By analyzing the precise shape of the light curve, Bond and
his team determined one smaller object is only 0.4 percent
the mass of a second, larger object. They concluded the
smaller object must be a planet orbiting its parent star.

Dr. Bohdan Paczynski of Princeton University, Princeton,
N.J., an OGLE team member, first proposed using
gravitational microlensing to detect dark matter in 1986. In
1991, Paczynski and his student, Shude Mao, proposed using
microlensing to detect extrasolar planets. Two years later,
three groups reported the first detection of gravitational
microlensing by stars. Earlier claims of planet discoveries
with microlensing are not regarded as definitive, since they
had too few observations of the apparent planetary
brightness variations.

“I’m thrilled to see the prediction come true with this
first definite planet detection through gravitational
microlensing,” Paczynski said. He and his colleagues believe
observations over the next few years may lead to the
discovery of Neptune-sized, and even Earth-sized planets
around distant stars.

Microlensing can easily detect extrasolar planets, because a
planet dramatically affects the brightness of a background
star. Because the effect works only in rare instances, when
two stars are perfectly aligned, millions of stars must be
monitored. Recent advances in cameras and image analysis
have made this task manageable. Such developments include
the new large field-of-view OGLE-III camera and the MOA-II
1.8 meter (70.8 inch) telescope being built and cooperation
between microlensing teams.

“It’s time-critical to catch stars while they are aligned,
so we must share our data as quickly as possible,” said OGLE
team-leader Dr. Andrzej Udalski of Poland’s Warsaw
University Observatory. Udalski in Poland and Paczynski in
the U.S lead the Polish/American project. It operates at Las
Campanas Observatory in Chile, run by the Carnegie
Institution of Washington, and includes the world’s largest
microlensing survey on the 1.3 meter (51-inch) Warsaw

NASA and the National Science Foundation fund OGLE in the
U.S. The Polish State Committee for Scientific Research and
Foundation for Polish Science funds it in Poland. MOA is
primarily a New Zealand/Japanese group, with collaborators
in the United Kingdom and U.S. New Zealand’s Marsden Fund,
NASA and National Science Foundation, Japan’s Ministry of
Education, Culture, Sports, Science, and Technology, and the
Japan Society support it for the Promotion of Science.

Images and information about the latest research are
available on the Internet at:

SpaceRef staff editor.