Odd space pairing discovered
By Jan TenBruggencate
Advertiser Science Writer
A brown dwarf — an object midway between a planet and a star — has been photographed orbiting as close to its star as our solar system's larger planets do.
University of Hawai'i via Associated Press
That's something astronomers did not know could happen.
A brown dwarf, lower left, was recently discovered in close orbit around a star 58 light years from Earth.
The discovery, using the Gemini North and Keck II telescopes atop Mauna Kea, opens a whole field of new possibilities in astronomy, said Michael C. Liu, the University of Hawai'i postdoctoral researcher who announced the finding yesterday at the 199th meeting in Washington of the American Astronomical Society.
"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 sunlike stars," Liu said.
The sighting was made possible by high-tech "adaptive optics" equipment on both telescopes. This technology allows astronomers to remove the distorting effects of the Earth's atmosphere as they view the stars.
Liu and researchers from the University of California at Berkeley and the Carnegie Institution's Department of Terrestrial Magnetism studied a star the size of our own sun in the constellation Sagitta. The star is about 58 light years from Earth.
They found that the star, known as 15 Sge, has a companion, the brown dwarf, orbiting at a distance equivalent to somewhere between the orbits of Saturn and Uranus in our solar system.
Brown dwarfs are huge gaseous objects not quite large enough to support fusion, which would allow them to glow like stars. Some are "free-floating in space" like stars, Liu said, but others, like the one orbiting 15 Sge, act like planets. This one is about 60 times the mass of Jupiter—our largest planet—but just 7 percent the mass of its star. Its temperature is roughly 1,500 degrees Kelvin, a third to a quarter its star's temperature.
One of the interesting issues the discovery raises is just how that system, with its star and brown dwarf, originated. Our solar system is believed to have developed from a disc of gas and dust around our sun.
"This companion is probably too massive to have formed the way we believe that planets do," Liu said. "This finding suggests that a diversity of processes act to populate the outer regions of other solar systems."
Liu said the brown dwarf is too close to its sun to be viewed using standard telescopes.
"Only by using adaptive optics to produce very sharp images could we have found this companion," he said.
Earlier research found that the star 15 Sge has no planets in a closer orbit — the region in which our sun's Mercury, Venus, Earth and Mars are found, Liu said.
