JHU Device Helps Locate Brown Dwarf


Emil Venere
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Homewood News and Information

     Using an image-sharpening device designed and built at
Hopkins, astronomers at Hopkins and the California Institute of
Technology have made the first confirmed discovery of something
resembling a planet orbiting a star. 

     The astronomers--relying on the adaptive optics coronagraph
mounted on a telescope at Mount Palomar in California--found and
photographed a brown dwarf, a cosmic object too massive to be a
planet but too small and cool to shine like a star, in orbit
around a star 19 light-years from Earth in the constellation
Lepus. The discovery marks the first time astronomers can be
certain that they have identified a brown dwarf. Details of the
observation, confirmed by the Hubble Space Telescope on Nov. 17
at the Palomar Observatory in southern California, were published
in the Nov. 30 issue of the British journal Nature.

     Brown dwarfs are thought to be failed stars; they did not
start out with enough mass to generate the high temperatures
needed to bring about nuclear fusion, which makes stars shine.

     Astronomers have long been able to observe stars orbiting
other stars, in so-called binary star systems, but the
Caltech/Hopkins discovery marks the first time that a more
planet-like object has been observed in orbit around a star. The
team of astronomers deduce that the object is about 20 times more
massive than Jupiter, even though it probably is about the same
size as Jupiter.

     It orbits a red-colored star called Gliese 229, some 112
trillion miles from Earth.

     "This is clearly a brown dwarf," said Samuel Durrance, a
Hopkins astrophysicist who conceived the idea for the adaptive
optics coronagraph, which was needed to make the crisp images.
"One difference between planets and brown dwarfs lies in how they
formed." The brown dwarf, named GL 229B, is probably similar in
many respects to the large gaseous planets in our solar system,
he said. 

     The astronomers suspect that the brown dwarf developed
during the normal star-formation process as one of two members of
a binary system. The brown dwarf did not acquire enough mass to
become a star. Astronomers cannot yet rule out the possibility
that GL 229B formed as a super-size planet. 

     All of the planets in our solar system, including the large
gaseous planets like Jupiter and Saturn, are believed to have
formed from material in a primeval disk of dust around our
newborn sun. They did not start out as potential stars.

     The discovery of GL 229B comes three years into a long-term
project to search for "low-mass" companions of stars near Earth.
The brown dwarf was first observed in October 1994 using the
adaptive optics device and a 60-inch reflecting telescope at
Mount Palomar, said David Golimowski, an associate research
scientist in the Department of Physics and Astronomy.

     Golimowski, who has been involved in designing and building
the coronagraph since its inception, was one of the astronomers
who made the historic observation. It took another year to
confirm that the object was actually an orbiting companion of the
star. Although the astronomers do not know the brown dwarf's
orbit, they estimate that its distance from the star is at least
the same as Pluto's from the sun, about 4 billion miles. 

     "I don't want to say this is the discovery of a lifetime
because I'm hoping that the rest of my astronomical career will
be filled with things like this," said the 32-year-old
Golimowski. "This has been sort of the holy grail for a lot of
people."