Brown dwarf stars

November 28, 1997

Universities in the Canary Islands have learned the benefits of working together. Rebecca Warden reports

THE Astrophysics Institute of the Canaries was founded in the 1960s when Spain's first professor of astrophysics, Francisco Sanchez, came to the Canaries.

"Spanish astrophysics was born at the University of La Laguna using the Canaries skies as its natural resource," Professor Sanchez says. "Before that there was simply no tradition in Spain."

The institute houses powerful telescopes at two observatories on Tenerife and La Palma, enjoys an international reputation for the quality of its research and ranks among the top three places for sky-watching alongside observatories in Hawaii and in Chile's Atacama desert.

It was a team of IAC scientists that announced the first sighting of a brown dwarf in a paper published in December 1995. This was confirmed by a meeting of leading astrophysicists held in the Canaries in March this year.

A brown dwarf is a cool object similar to a star, but is incapable of sustaining nuclear fusion because of its insufficient mass. Whereas stars give off a large amount of light as a product of nuclear fusion, brown dwarfs have only faint luminosity at the start of their lives, becoming fainter and fainter as they cool and shrink in size, making them very hard to detect.

"We adopted the strategy of looking for brown dwarfs when they are young and give off more light as this helps us to reach them with telescopes," says scientist Ms Zapatero Osorio. "We also decided to search in regions of the sky where the density of objects is greater than in other regions, for example, where stars are born."

Their efforts paid off when they discovered Teide 1 in the region of the Pleiades star cluster. Scientists have since located several more brown dwarfs, including some near the sun.

The next task is to study the characteristics of these phenomena and work out how frequently they occur. While brown dwarfs are always smaller than stars, another question is how small they can be.

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