And scientists have struggled and argued over the
specific differences between brown dwarfs and planets,
especially how and where they are born. Finding a brown
dwarf in a region around a star thought to be reserved
for planets will only exacerbate ongoing disagreements.
"This finding suggests that a diversity of processes
act to populate the outer regions of other solar
systems," said Michael Liu, a University of Hawaii
astronomer who led the team that made the discovery.
Liu and his colleagues, a group of venerable planet
hunters, found the object using the Gemini North and
Keck telescopes at Mauna Kea, Hawaii. The results were
presented here at a meeting of the American Astronomical
The brown dwarf is just 14 Astronomical Units away
from the star (1 AU is the distance from Earth to the
Sun). Saturn is 10 AU from the Sun, and Uranus, the next
planet out, is 19 AU. The object is between 55 and 78
times as massive as Jupiter, which is the largest planet
in our solar system.
Researchers say the configuration of a star and such
a large, close companion can't be explained by current
theories of solar system formation.
Stars are created by the gravitational collapse of a
cloud of material. Planets, however, are thought to
develop out of a flat, rotating disk of material left
over from the creation of a star. Planet evolve when
smaller rocks, like comets and asteroids, get together.
Jupiter and the other gas giant planets probably have
origins in such rocky cores, which grew large enough to
attract a huge gas envelope, most astronomers
"This [brown dwarf] companion is probably too massive
to have formed the way we believe that planets do," Liu
Many stars also are known to form as pairs, orbiting
There's little question that the newly found object
is a brown dwarf, said Alan Boss, a planet formation
theorist at the Carnegie Institution. It probably formed
out of the same cloud of material from which the star
formed, he said.
The presence of the brown dwarf might inhibit the
formation of planets, said Boss, who was not involved in
the research. Or, he said, it might actually foster the
development of planets, according to competing
Further study of this and similar systems will be
needed to learn how they form, the researchers
Hints of the brown dwarf were initially spotted a
decade ago by a team of extrasolar planet hunters.
Geoff Marcy and Debra Fischer at the University of
California at Berkeley, along with Paul Butler of the
Carnegie Institution, have helped find many of the 80 or
so known extrasolar planets. Their technique, which
notes slight wobbles in a star caused by large,
closely-orbiting planets, could not definitively
identify what they suspected was a brown dwarf farther
out from a star called HR 7672, which is 58 light-years
away from Earth.
Current techniques cannot find small planets, either.
The extrasolar planets that have been identified in the
past 5 years are all very large. Most are bigger than
Jupiter and orbit very close to their host stars. Some
are as close as Mercury is to our Sun.
Already, astronomers were struggling to explain how
planets so large could exist so close to stars. And they
wonder whether this is normal, or whether other solar
systems like ours might be the norm but simply have
eluded detection so far.
The answer bears on whether there are other
Earth-like planets out there, which might support
Answers won't come, however, until technology allows
for the discovery of small extrasolar planets, assuming
they exist. One space-based observatory that would do
this, called Kepler, was in late December and is scheduled to
launch in 2006. Kepler would succeed by doing its
observing from above the blurring effects of Earth's
Other researchers are working to stretch ground-based
observation techniques beyond current limits to allow
for the discovery of smaller planets and of large
objects orbiting far from stars. The new discovery
represents one of these efforts.
How it was found
Brown dwarfs generate enough heat to shine, but only
dimly and in infrared light.
The newly spotted brown dwarf was found using a
relatively new technique called adaptive optics, which
corrects for some of the blurring effects of Earth's
atmosphere and allows faint objects to be photographed
with resolution that can be 10 times better.
Liu imaged the primary star HR 7672 (also called 15
Sge) last summer, and he noticed a dim spot of light
next to it, described as being akin to a firefly next to
a bright searchlight. Follow-up images, using adaptive
optics, showed the faint object moved on the sky along
with the primary star, proving that it was in fact a
companion and not a background star.
HR 7672 is slightly younger than our Sun, but
otherwise is seen as a twin to the Sun, Liu said. The
researchers are now looking for similar groupings of
other stars and brown dwarfs.
"Now that we know brown dwarfs exist in the region of
giant planet formation, we would like to understand how
often these oddball pairings occur in the universe, and
what that can tell us about the alternate and divergent
ways in which solar systems form around Sun-like stars,"
James Graham and James Lloyd, also from the
University of California at Berkeley, contributed to the
Next up: Jupiter-sized planets
Boss said the results were a tantalizing appetizer of
a feast of observations expected in the near future from
adaptive optics systems.
"It's basically changing an astronomical image from
something that looks like a very fuzzy impressionistic
painting into something that looks like a photo-realist
painting," Boss said.
Ray Jayawardhana, a researcher at the University of
California, Berkeley, said he expects the technique to
provide direct images of Jupiter-sized planets around
other stars soon, possibly within two years. Several
groups are competing to achieve that goal, he said, and
already there are candidate objects that they are
examining more closely.
"It might seem crazy," Jayawardhana said, but it's
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