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Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Brown Dwarfs Get Hot
8 June 2001 7:00 pm
PASADENA, CALIFORNIA--The surprising heat from 63 brown dwarfs is helping astronomers make the case that these puzzling objects are failed stars, and not big planets, as some have argued. But even though they fail to shine, the dwarfs may still leave a legacy. The heat suggests that the dwarfs are wrapped in a dusty disk of the kind that typically give birth to planets, a team reported here on 7 June at a meeting of the American Astronomical Society.
In the past 5 years, a misfit class of gaseous balls has been discovered orbiting nearby stars or floating freely through space (ScienceNOW, 5 October 2000 and 26 February 2001). It's hard to know how they formed: The brown dwarfs seem too heavy to have formed from the slow agglomeration of material, like jumbo-sized planets such as Jupiter. Yet they are too light to ignite the nuclear fusion that powers stars. Confused astronomers named the objects failed stars, superplanets, or simply brown dwarfs. But they admit they didn't really know which were stars and which were planets.
At least part of the question has now been answered: The free-floating brown dwarfs are stars. Although brown dwarfs have no nuclear fire in their belly, they are hot enough to emit infrared radiation, just like a human body. And if they formed from contracted clouds like a star, a warm dusty disk should orbit the dwarf and radiate a lot of additional infrared light. It was precisely this extra light that astrophysicist Charles Lada of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, was looking for when his team surveyed 100 free-floating brown dwarfs in the nearby Trapezium star cluster in March 2000, using the 3.5-meter New Technology Telescope in Chile. They found it in 63 dwarfs. An oversized free-floating planet formed by agglomeration would not have a disk, explains Lada, so these dwarfs must have formed like stars. And the disks could spawn small, inhospitable planets, he says.
"This is compelling evidence," says Geoff Marcy, an astronomer at the University of California, Berkeley. And although he is confident that the disks are real, Marcy points out that astronomers' models of brown dwarfs are still in their infancy, and it's hard to predict exactly how much heat they produce. Further refinements in brown dwarf models should soon reduce that uncertainty, he says.