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Astronomers discover youngest and lowest-mass brown dwarfs

The three substellar objects lie 1,000 light-years away in the star-forming region IC 348.
Provided by the Royal Astronomical Society, United Kingdom
IC 348 and NGC 1333 region
Astronomers have found three brown dwarfs with estimated masses of less than 10 times that of Jupiter in the star-forming region IC 348.
Adam Block and Tim Puckett
April 22, 2009
Astronomers have found three brown dwarfs with estimated masses of less than 10 times that of Jupiter, making them among the youngest and lowest-mass substellar objects detected in the solar neighborhood to date.

A team of astronomers working at the Laboratoire d'Astrophysique de l'Observatoire de Grenoble (LAOG) in France made the observations using the Canada France-Hawaii Telescope (CFHT). Andrew Burgess presented the discovery at the European Week of Astronomy and Space Science at the University of Hertfordshire in the United Kingdom April 22.

The team found the dwarfs in a star-forming region named IC 348, which lies almost 1,000 light-years from our solar system toward the constellation Perseus. This cluster is approximately 3 million years old — extremely young compared to our 4.5-billion-year-old Sun — which makes it a good location to search for the lowest-mass brown dwarfs. The dwarfs are isolated in space, which means that they are not orbiting a star, although they are gravitationally bound to IC 348. Their atmospheres all show evidence of methane absorption, which was used to select and identify these young objects.

"There has been some controversy about identifying young, low-mass brown dwarfs in this region," Burgess said. "An object of a similar mass was discovered in 2002, but some groups have argued that it is an older, cooler brown dwarf in the foreground coinciding with the line of sight. The fact that we have detected three candidate low-mass dwarfs towards IC 348 supports the finding that these really are very young objects."

The team set out to find a population of these brown dwarfs in order to help theoreticians develop more accurate models for the distribution of mass in a newly formed population, from high-mass stars to brown dwarfs, which is needed to test current star-formation theories. The discovery of the dwarfs in IC 348 has allowed the team to set new limits on the lowest-mass objects.

"Finding three candidate low-mass dwarfs towards IC 348 backs up predictions for how many low-mass objects develop in a new population of stars," Burgess said. "Brown dwarfs cool with age, and current models estimate that their surfaces are approximately 900 to 1000 degrees Kelvin (about 1150° to 1350° Fahrenheit [600° to 700° Celsius]). That's extremely cool for objects that have just formed, which implies that they have the lowest masses of any of this type of object that we've seen to date."
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