Runt of the universe found

April 7, 2000

It is the runt of our galaxy's stellar litter. The smallest brown dwarf, a "failed" star that barely glimmers, has been detected by astronomers.

Weighing in at just less than ten times the mass of Jupiter, or about 1 per cent the mass of the Sun, it is the lightest non-planetary object yet seen outside the solar system.

However, David Pinfield, the astronomer at Queen's University, Belfast, who made the discovery, believes the runt and its ilk could emerge as our galaxy's silent majority, outnumbering and possibly outweighing ordinary stars.

They could even hold the key to explaining dark matter, the mysterious "invisible" substance that some have calculated could account for nine-tenths of the mass of all galaxies.

"Brown dwarfs could be all around us in the local galactic disk, but we wouldn't see them all, as many of them would just be too faint and cool," he said.

Dr Pinfield, who described his research at a conference in Dublin last week, has so far identified 132 candidate objects, 92 of which potentially have a mass under ten times that of Jupiter.

Brown dwarfs are made up of hydrogen, like our Sun, but have too little mass to start the nuclear reactions that make stars shine. Instead they are doomed to simply cool and shrink with age.

Dr Pinfield trained the Isaac Newton Telescope at a star-forming region called the Taurus molecular cloud.

He has since begun to check his candidates using the United Kingdom Infrared Telescope and, of the three completed so far, two have been confirmed as brown dwarfs.

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