Amid space clouds stuffed with baby stars, astronomers have detected 30 difficult-to-spot brown dwarfs, failed stars that emit very little radiation.
The dusty clouds are near the star rho Ophiuchi, located 540 light-years away in the constellation of Ophiucus. Nesting in these clouds are more than 100 newborn stars -- large, bright and obvious.
But using the European Space Agency's Infrared Space Observatory (ISO), astronomers also detected the faint heat signatures of the brown dwarfs.
Brown dwarfs are objects that never gathered enough mass to generate the thermonuclear fusion that powers real stars and makes them shine in visible light. Relatively few of these brown dwarfs have been identified so far, due to their low levels of energy emission.
"ISO gives us a new, really rich sample of young brown dwarfs in the rho Ophiuchi region," said Sylvain Bontemps of the Observatoire de Bordeaux in France. "We will clearly have to go back and search for more of these sub-stellar objects with current and future infrared telescopes, both in space and from the ground."
The findings were made by international team led by Lennart Nordh of Stockholm Observatory in Sweden.
The nature of brown dwarfs is not entirely known, and their definition is still being worked out. Some astronomers say that at least some brown dwarfs, the less massive ones, could be better described as giant planets, like Jupiter, instead of as failed stars. The minimum mass for a star to shine is roughly 8 per cent of the mass of the Sun, or 80 times the mass of Jupiter. Below that limit, the 'nuclear oven' that provides the star's energy cannot be ignited at the star's core.
In the case of the brown dwarfs found in the rho Ophiuchi region, "the less massive are about 5 percent of the mass of the Sun, or 50 Jupiter masses," Bontemps said. "But certainly there could still be less massive objects hidden in the dust."
The newly found brown dwarfs are typically a million years old -- young by stellar standards. As a consequence they are still relatively bright in the infrared compared to older brown dwarfs.
An image that accompanies the finding does not reveal the brown dwarfs to the untrained eye. But there is much to explore in the picture.
Three of the brightest young stars in the stellar nurseries are easy to find: one in the center of the right-hand-side border; a second one in the middle of a comet-shaped nebula in the lower-right of the image; and one in the middle of the small nebula close to the center-right.
Other point-like sources are also young stars and 'protostars' -- fledgling stars that are still growing by sucking in gas from the cloud.
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