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	Closest Failed Star to Earth Found to Have Failed Companion, Too By Robert Roy Britt Senior Science Writer posted: 04:30 pm ET 19 September 2003

Astronomers have found relatively nearby lightweight star in a configuration never before seen

Astronomers have found a lightweight star in a configuration never before seen relatively close to our solar system. The star is a cool and dim brown dwarf orbiting another similar brown dwarf. Both objects are like failed stars, with not enough mass to generate the thermonuclear fusion that powers the Sun.

Both brown dwarfs, together, orbit a regular star. Triple star systems are fairly common, but this is the first known to involve a double brown dwarf.

Brown dwarfs are hard to find because they emit almost no light. They are typically at least 30 times as massive as Jupiter and, because of their heft and heat radiation, are not considered planets. Some astronomers refer to them as substellar.

The system of three objects is just 11.8 light-years away. The main star, called Epsilon Indi, is similar to our Sun and resides in the skies above Earth's Southern Hemisphere. In January, astronomers found a brown dwarf around the star and named it Epsilon Indi B. It is the closest known brown dwarf. And now it has been renamed Epsilon Indi Ba to make classification room for its companion.

The newfound brown dwarf, even cooler and dimmer than Epsilon Indi Ba, is called Epsilon Indi Bb, and it orbits the other brown dwarf. In reality, because the masses of the two objects are not greatly different, they go around each other.

Here's the configuration: Epsilon Indi Ba is about 1,500 times as far from Epsilon Indi as Earth is from our Sun. Astronomers term this 1,500 astronomical units, or AU. Epsilon Indi Bb orbits Epsilon Indi Ba much more closely, at a distance of at least 2.2 AU.

"When the target was acquired and we saw that there were clearly two objects close together, we initially thought it must be the wrong object," said Kevin Volk of the Gemini Observatory in Chile. "Epsilon Indi Ba had been observed before and in those observations, no one noticed the companion object. It was a tremendous surprise for us."

The second brown dwarf in the system was spotted independently by two groups within days of each other. The Gemini Observatory team was led by Gordon Walker of the University of British Columbia in Vancouver, Canada. The other team was led by Mark McCaughrean of the Astrophysical Institute in Potsdam, Germany, using the European Southern Observatory's Very Large Telescope in Chile.

In January, when astronomers thought they were dealing with just one brown dwarf, they put its mass at roughly 50 times that of Jupiter. Now the two objects are thought to be about 44 and 28 times Jupiter's mass. The two teams developed different masses for the brown dwarfs, however.

Further research is expected to reveal more information about the objects.

Both brown dwarfs are thought to have diameters roughly similar to that of Jupiter, but they are much more dense and, because of the resulting pressure on their cores, glow with a fairly intense heat that Jupiter does not produce.

The closest known star system is Alpha Centauri, at just 4.36 light-years away. It contains three stars, all of them shining brightly.

Experts won't be surprised if a brown dwarf is eventually found at a similar close distance. In fact, some say, there could be as many brown dwarfs in the galaxy as stars. Some researchers have even argued that a brown dwarf or other star of some sort, tagged Nemesis, might be so close as to orbit around our own Sun. There is no solid evidence, however, for any such mystery object.