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Cosmos Provides Astronomers with Planet-Hunting Tool

This is an artist's rendering of the planet, believed to be one-and-a- half times larger than Jupiter, orbiting a red dwarf, its parent star. The distance between the star and planet is three times the distance between Earth and the Sun. If only astronomers had a giant magnifying glass in space, they might be able to uncover planets around other stars. Now they do -- sort of. Instead of magnifying a planet, astronomers used the magnifying effects of one star on a more distant star to reveal a planet around the closer star. The discovery marks the first use of a celestial phenomenon known as microlensing to locate a planet outside our solar system. A star or planet can act as a cosmic lens to magnify and brighten a more distant star lined up behind it. That's because 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 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 that 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.

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.

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Further Reading
The Sky Observer's Guide: A Handbook for Amateur Astronomers
by R. Newton Mayall

Related Web Links
Planet Hunting
by Jet Propulsion Laboratory

Planet Hunters on Trail of Worlds Smaller than Saturn Space Telescope Science Institute
by Space Telescope Science Institute

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