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.
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.
"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.
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