3:58 p.m., Monday, January 7, 2002
UH astronomers find planet-like
Associated Press Science Writer
have captured a direct image of a massive, planet-like
object called a brown dwarf in close orbit of a distant
star very much like the sun.
a University of
Hawai'i astronomer, said the brown dwarf orbits
around its parent star at slightly less than the
distance between the sun and the planet Uranus. The new
discovery orbits closer to its parent star than any
other brown dwarf yet discovered, said Liu.
North Telescope adaptive optics image shows 15
Sge and its newly found companion 15 Sge B,
smaller dot, lower left. The image has been
computer-processed to subtract the ligth from the
much brighter primary star.
Observatory/University of Hawai'i Institute for
technology that sharpens the view of ground-based
telescopes, astronomers found the brown dwarf orbiting
about 1.3 billion miles from the star known as 15 Sge in
the constellation Sagitta, located about 58 light years
from Earth. Uranus orbits the sun at about 1.7 billion
miles. A light year is the distance light will travel in
a year, about 6 trillion miles.
discovery implies that brown dwarf companions to
average, sun-like stars exist at a separation comparable
to the distance between the sun and the outer planets in
our solar system," Liu said. He announced his discovery
today at the national meeting of the American
Liu said the
parent star of the brown dwarf is "basically the same as
our sun. It's like a clone of our sun, a solar
brown dwarf so close to the star suggests that solar
systems formed around sun-like stars could come in many
different shapes and planetary distributions. Liu said
it is possible that there are planets similar to Earth
circling the star inside the orbit of the brown dwarf.
For instance, it would be possible for a planet to orbit
the star at 93 million miles, the distance from Earth to
A brown dwarf,
sometimes called a "failed star," is bigger than a
planet but much smaller than a star. They are thought to
be balls of gas that failed to collect enough mass to
start shining. Astronomers believe that a stellar object
must have at least 8 percent of the mass of the sun for
there to be enough internal pressure to start the
nuclear fires that cause stars to shine.
Liu said the
discovered brown dwarf is 55 to 78 times the mass of
Jupiter, the largest planet in the solar system. Jupiter
is 318 times more massive than Earth.
brown dwarf in close orbit of a sun-like star is a rare
event. The objects are difficult to see because of the
glare of the central star. Astronomers compare the feat
to detecting a firefly next to a searchlight. In the
past, ground-based telescopes were unable to make such
observations because light arriving from distant stars
is distorted by the Earth's atmosphere.
Liu said the
orbiting brown dwarf was found using a new telescope
technique called adaptive optics. The system, installed
on two telescopes in Hawai'i, use a flexible mirror that
is constantly being bent slightly to compensate for the
distortion of the atmosphere.
"Only by using
adaptive optics to produce very sharp images could we
have found this companion," said Liu. "It is too faint
and too close to its parent star to be seen