HOW THEY STACK UP: The difference between brown dwarfs and planets.
For several years, astronomers have struggled to distinguish between planets, stars, and in-between objects known as brown dwarfs.
Brown dwarfs are generally thought to be more massive than planets, but not hefty enough to ignite the thermonuclear fusion that powers a normal star.
So things get really confusing when a brown dwarf has an object orbiting it. Is that a planet?
Things get even more confusing when, as now, astronomers discover a modest brown dwarf -- one with a mass that could be considered planet-like -- that looks as if its about to spawn planet-like objects.
A team led by Kevin Luhman of Penn State University announced Tuesday the discovery of a brown dwarf just eight times the mass of Jupiter. It's considered a brown dwarf in part because it formed alone in space, not orbiting anything else. And it is encircled by a disk of material that looks very much like planet-forming regions seen around real stars.
Nobody knows if the gas and dust in the disk will coalesce into planets. But Luhman speculates that the newfound setup could evolve into a miniature solar system.
"Here we have a Sun that is so small it is the size of a planet," he said. "The question then becomes, what do we call any little bodies that might be born from this disk: planets or moons?"
"Some go by size, and others go by how the object formed," says study team member Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics. "For instance, this new object would be called a planet based on its size, but a brown dwarf based on how it formed."
Luhman and colleagues studied the brown dwarf, called Cha 110913-773444, with NASA's Spitzer Space Telescope, the Hubble Space Telescope, and two telescopes in the Chilean Andes, the Blanco telescope of the Cerro Tololo Inter-American Observatory and the Gemini South telescope.
The object is 500 light-years away in the constellation Chameleon. It is about 2 million years old. Our Sun is about 4.6 billion years old.
The results will be detailed in the Dec. 10 issue of Astrophysical Journal Letters.
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