Is New Brown Dwarf 'Appetizer' in Planetary Feast?

By Deborah Zabarenko

WASHINGTON (Reuters) - A newly detected brown dwarf orbiting a sun-like star in Earth's cosmic neighborhood could be just the first course in an upcoming banquet of planetary discovery, astronomers said on Monday.

The brown dwarf, a failed star with about 65 times the mass of Jupiter, was detected by astronomers who used two large telescopes on the Big Island of Hawaii. The telescopes were equipped with so-called adaptive optics technology, which corrects for the blurring of Earth's atmosphere.

Astronomers have discovered dozens of objects orbiting stars outside our solar system in the last decade, but this is the closest one they have seen directly. The others generally have been found indirectly, by observing the gravitational pull they exert on the stars they orbit.

One of the big Hawaiian telescopes, the Gemini North, also was used to find a protoplanetary disk -- the platter of cosmic dust that gives birth to planetary systems -- in a four-star system.

The fact that both these observations were made with ground-based telescopes, rather than the Hubble Space Telescope (news - web sites) orbiting above the distorting atmosphere, could mean that a new era in planetary science is dawning, scientists said at a meeting of the American Astronomical Society in Washington.

``I think these discoveries are both marvelous, but in many ways they're really just a very tantalizing appetizer for what's to come,'' said Alan Boss of the Carnegie Institute of Washington.

``In the next few years, we're likely to find ... a feast of results from adaptive optics systems that function very well on large telescopes,'' Boss said.

HAWAII'S TELESCOPES COMPETE WITH HUBBLE

For Ray Jayawardhana, an astronomer at the University of California, Berkeley who detected the protoplanetary disk in the four-star system, adaptive optics made his discovery possible.

``We could never have resolved the star (as it first appeared) into a pair (of stars) without adaptive optics,'' Jayawardhana said at a news conference. For the future, he said, ``It is now technically possible to detect a young Jupiter around a nearby star.''

To detect the brown dwarf around the star 15 Sge in the constellation Sagitta (''the arrow''), about 57.7 light-years from Earth, astronomer Michael Liu of the University of Hawaii used the Gemini North telescope and adaptive optics.

A light-year is about 6 trillion miles (10 trillion km), the distance light travels in a year.

The star 15 Sge is barely visible to the naked eye on a clear night far from any city lights. Its faint brown dwarf companion is not visible without adaptive optics.

The presence of a brown dwarf orbiting this star could mean that planetary systems form in many ways, not just from a disk of dust and gas swirling around young stars, Liu said.

Jayawardhana said the adaptive optics capabilities of ground-based telescopes, such as Gemini North and Keck on the dormant volcano of Mauna Kea, mean they can compete with the orbiting Hubble. But he stopped short of saying they could replace it.

``You need to use the right tools for every job, so Hubble still has a very significant place,'' Jayawardhana said. ``But Hubble is still only one telescope, so not every astronomer in the world who wants Hubble time can get Hubble time. ... But it does show that ... (large) ground-based telescopes do compete with Hubble on certain kinds of science.''

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