Cosmic census finds universe full of brown dwarves

larger   A swarm of brown dwarf stars are revealed in the top image of the Orion Nebula's Trapezium cluster taken by the Hubble's near-infrared camera. The image below, also obtained by the Hubble, shows the nebula as it appears in a visible light

By Richard Stenger
CNN.com Writer

(CNN) -- Once considered rare, brown dwarves populate the cosmos with surprising regularity, according to astronomers studying the elusive objects, which occupy a limbo between stars and planets.

Using the Hubble Space Telescope, scientists conducted unparalleled inventories of two young star clusters in search of brown dwarves, which lack sufficient mass to ignite into stars.

Astronomers considered the dim gaseous spheres an oddity only a few years ago. They emit light so faintly that they are difficult to spot. But in related discoveries announced Thursday, two scientific teams said they found brown dwarves liberally scattered throughout the stellar nurseries.

"It looks like they are as ubiquitous as stars. Where you see stars you will see brown dwarves," said Glenn Tiede, a researcher at the National Optical Astronomy Observatories (NOAO) in Tucson, Arizona, who helped conduct one of the inventories.

Too large to be planets and too small to be stars, brown dwarves are known to exist in a wide variety of sizes, ranging from 80 to 15 times the mass of Jupiter. Larger gas objects ignite into stars. Smaller ones generally remain hidden from even the most sophisticated orbiting observatories.

However, by studying relatively young and bright brown dwarves, one team found some as small as 10 times the mass of Jupiter, according to the Space Telescope Science Institute in Baltimore, Maryland, which manages the Hubble telescope.

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The Hubble census conducted by NOAO astronomers and a Naval Research Laboratory colleague revealed that, like stars, there are more brown dwarves with low masses than high masses. The trend continues downward to nearly planetary masses.

"The sequence of mass does not change when you cross from stars to brown dwarves," Tiede said.

Many questions remain about the evolution of brown dwarves. The answers could help explain the genesis of other celestial bodies.

"Because the brown dwarves 'bridge the gap' between stars and planets, their properties reveal new and unique insights into how stars and planets form," said NOAO astronomer Joan Najita in a statement.

The studies, which together tallied a total of 80 brown dwarves, will be published in the Astrophysical Journal in September and October.

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Space Telescope Science Institute
Hubble Heritage Project
Hubble SM3A
National Optical Astronomy Observatories
Naval Research Laboratory
The Astrophysical Journal

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